RT8205L/M

High Efficiency, Main Power Supply Controller

for Notebook Computer
General Description Features
The RT8205L/M is a dual step-down, switch mode power z Constant On-time Control with 100ns Load Step
supply controller generating logic-supply voltages in Response
battery powered systems. It includes two Pulse-Width z Wide Input Voltage Range : 6V to 25V
Modulation (PWM) controllers adjustable from 2V to 5.5V, z Dual Adjustable Outputs from 2V to 5.5V
and also features fixed 5V/3.3V linear regulators. Each z Secondary Feedback Input Maintains Charge Pump
linear regulator provides up to 100mA output current with Voltage (RT8205M)
automatic linear regulator bootstrapping to the PWM z Fixed 3.3V and 5V LDO Output : 100mA
outputs. An optional external charge pump can be z 2V Reference Voltage
monitored through SECFB (RT8205M). The RT8205L/M z Frequency Selectable via TONSEL Setting
includes on-board power up sequencing, a power good z 4700ppm/°°C RDS(ON) Current Sensing
output, internal soft-start, and internal soft-discharge z Programmable Current Limit Combined with
output that prevents negative voltage during shutdown. Enable Control
z Selectable PWM, DEM, or Ultrasonic Mode
The constant on-time PWM control scheme operates
z Internal Soft-Start and Soft-Discharge
without sense resistors and provides 100ns response to
z High Efficiency up to 97%
load transient response while maintaining nearly constant
z 5mW Quiescent Power Dissipation
switching frequency. To eliminate noise in audio
z Thermal Shutdown
applications, an ultrasonic mode is included, which
z RoHS Compliant and Halogen Free
maintains the switching frequency above 25kHz. Moreover, http://www.DataSheet4U.net/

the diode-emulation mode maximizes efficiency for light

Applications
load applications. The RT8205L/M is available in a
WQFN-24L 4x4 package. z Notebook and Sub-Notebook Computers
z 3-Cell and 4-Cell Li+ Battery-Powered Devices
Ordering Information
RT8205
Package Type
QW : WQFN-24L 4x4 (W-Type)
Lead Plating System
G : Green (Halogen Free and Pb Free)
Z : ECO (Ecological Element with
Halogen Free and Pb free)
Pin Function
L : Default
M : With SECFB
Note :
Richtek products are :
` RoHS compliant and compatible with the current require-
ments of IPC/JEDEC J-STD-020.
` Suitable for use in SnPb or Pb-free soldering processes.

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RT8205L/M
Marking Information
RT8205LGQW RT8205MGQW
EM= : Product Code EN= : Product Code
EM=YM YMDNN : Date Code EN=YM YMDNN : Date Code
DNN DNN

RT8205LZQW RT8205MZQW
EM : Product Code EN : Product Code
EM YM YMDNN : Date Code EN YM YMDNN : Date Code
DNN DNN

Pin Configurations
(TOP VIEW)
UGATE1

UGATE1
PHASE1

PHASE1
LGATE1

LGATE1
PGOOD

PGOOD
BOOT1

BOOT1
VOUT1

VOUT1
24 23 22 21 20 19 24 23 22 21 20 19
ENTRIP1 1 18 NC ENTRIP1 1 18 SECFB
FB1 2 17 VREG5 FB1 2 17 VREG5
REF 3 16 VIN REF 3 16 VIN
GND GND
TONSEL 4 15 GND TONSEL 4 15 GND
FB2 5 25 14 SKIPSEL FB2 5 25 14 SKIPSEL
ENTRIP2 6 13 EN ENTRIP2 6 13 EN
7 8 9 10 11 12 http://www.DataSheet4U.net/
7 8 9 10 11 12
VOUT2
VREG3
BOOT2
UGATE2
PHASE2

VOUT2
LGATE2

VREG3
BOOT2
UGATE2
PHASE2
LGATE2

WQFN-24L 4x4 WQFN-24L 4x4

RT8205L RT8205M

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 RT8205L/M
Typical Application Circuit
VIN
6V to 25V
R8
C1 3.9 RT8205L R10 C13 C12
10µF 0 Q2 10µF 10µF
16 VIN UGATE2 10 BSC119
C10
0.1µF 9 RBOOT2 0 N03S
BOOT2
C11 L2
Q1 R4 0 21 UGATE1 0.1µF 4.7µH VOUT2
BSC119 PHASE2 11 3.3V
N03S RBOOT1 0 Q4
22 BOOT1 LGATE2 12 BSC119 R11 C17
220µF
L1 C2 GND 15 N03S
6.8µH 0.1µF C14
VOUT1 20 PHASE1
5V VOUT2 7
C3 Q3 19 LGATE1
R5 5 C21
220µF BSC119 FB2 R14
RILIM1 6.5k
N03S 150k
C4
ENTRIP1 1 C20
24 VOUT1 R15 0.1µF
RILIM2
150k 10k
C18 R12 6
ENTRIP2
15k
2 FB1 25 (Exposed Pad)
C19 GND
R13 VREF 3 REF
0.1µF 2V C15
10k
0.22µF VREG5 17 5V Always On
C9
4 TONSEL 4.7µF R6
Frequency Control 100k
14 SKIPSEL PGOOD 23 PGOOD Indicator
PWM/DEM/Ultrasonic
VREG3 8 3.3V Always On
ON 13 EN C16
4.7µF
OFF

VIN
6V to 25V
R8
C1 3.9 RT8205M R10 C13 C12
10µF 0 Q2 10µF 10µF
16 VIN UGATE2 10
http://www.DataSheet4U.net/

BSC119
C10
0.1µF 9 RBOOT2 0 N03S
BOOT2
C11 L2
Q1 R4 0 21 UGATE1 0.1µF 4.7µH VOUT2
BSC119 PHASE2 11 3.3V
N03S RBOOT1 0 Q4
22 BOOT1 LGATE2 12 BSC119 R11 C17
220µF
L1 C2 GND 15 N03S
C14
VOUT1 6.8µH 0.1µF
20 PHASE1
5V VOUT2 7
C3 Q3 19 LGATE1
R5 5 C21
220µF BSC119 FB2 R14
N03S RILIM1 6.5k
C4
150k C20
24 VOUT1 ENTRIP1 1 R15 0.1µF
RILIM2 10k
C18 R12 150k
15k 6
2 FB1 ENTRIP2

C19 25 (Exposed Pad)

R13 C5 GND
0.1µF D1 0.1µF
10k
C6
0.1µF D2 VREG5 17 5V Always On
C9
C7 4.7µF R6
D3 0.1µF 100k
D4 PGOOD 23 PGOOD Indicator

C8 BAT254 VREG3 8 3.3V Always On

R6 18 C16
0.1µF SECFB 4.7µF
200k R7
CP 39k REF 3 VREF
C15 2V
0.22µF
TONSEL 4 Frequency Control
ON 13 EN
SKIPSEL 14 PWM/DEM/Ultrasonic
OFF

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RT8205L/M
Functional Pin Description
Pin No. Pin Name Pin Function
Channel 1 Enable and Current Limit Setting Input. Connect a resistor to GND to
set the threshold for channel 1 synchronous RDS(ON) sense. The GND − PHASE1
1 ENTRIP1 current limit threshold is 1/10th the voltage seen at ENTRIP1 over a 0.515V to 3V
range. There is an internal 10μA current source from VREG5 to ENTRIP1. Leave
ENTRIP1 floating or drive it above 4.5V to shutdown channel 1.
SMPS1 Feedback Input. Connect FB1 to a resistive voltage divider from VOUT1
2 FB1
to GND to adjust output from 2V to 5.5V.
2V Reference Output. Bypass to GND with a minimum 0.22μF capacitor. REF
3 REF can source up to 100μA for external loads. Loading REF degrades FBx and
output accuracy according to the REF load regulation error.
Frequency Selectable Input for VOUT1/VOUT2 respectively.
400kHz/500kHz : Connect to VREG5 or VREG3
4 TONSEL
300kHz/375kHz : Connect to REF
200kHz/250kHz : Connect to GND
SMPS2 Feedback Input. Connect FB2 to a resistive voltage divider from VOUT2
5 FB2
to GND to adjust output from 2V to 5.5V.
Channel 2 Enable and Current Limit Setting Input. Connect a resistor to GND to
set the threshold for channel 2 synchronous RDS(ON) sense. The GND − PHASE2
6 ENTRIP2 current limit threshold is 1/10th the voltage seen at ENTRIP2 over a 0.515V to 3V
range. There is an internal 10μA current source from VREG5 to ENTRIP2. Leave
ENTRIP2 floating or drive it above 4.5V to shutdown channel 1.
Bypass Pin for SMPS2. Connect to the SMPS2 output to bypass efficient power
7 VOUT2
for VREG3 pin. VOUT2 is also for the SMPS2 output soft-discharge.
8 VREG3 3.3V Linear Regulator Output.
Boost Flying Capacitor Connection for SMPS2. Connect to an external capacitor
9 BOOT2 http://www.DataSheet4U.net/

according to the typical application circuits.

Upper Gate Driver Output for SMPS2. UGATE2 swings between PHASE2 and
10 UGATE2
BOOT2.
Switch Node for SMPS2. PHASE2 is the internal lower supply rail for the
11 PHASE2 UGATE2 high side gate driver. PHASE2 is also the current sense input for the
SMPS2.
Lower Gate Drive Output for SMPS2. LGATE2 swings between GND and
12 LGATE2
VREG5.
Master Enable Input. The REF/VREG5/VREG3 are enabled if it is within logic
13 EN
high level and disabled if it is less than the logic low level.
Operation Mode Selectable Input.
Connect to VREG5 or VREG3 : Ultrasonic Mode
14 SKIPSEL
Connect to REF : DEM Mode
Connect to GND : PWM Mode
15, Ground for SMPS Controller. The exposed pad must be soldered to a large PCB
GND
25 (Exposed Pad) and connected to GND for maximum power dissipation.
16 VIN Supply Input for 5V/3.3V LDO and Feed Forward On Time Circuitry.
5V Linear Regulator Output. VREG5 is also the supply voltage for the lower gate
17 VREG5
driver and analog supply voltage for the device.

To be continued
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 RT8205L/M
Pin No. Pin Name Pin Function
NC
No Internal Connection.
(RT8205L)
Charge Pump Control Pin. The SECFB is used to monitor the optional external 14V
18 charge pump. Connect a resistive voltage divider from the 14V charge pump output to
SECFB
GND to detect the output. If SECFB drops below the threshold voltage, LGATE1 will
(RT8205M)
provide 33kHz switching frequency for the charge pump. This will refresh the external
charge pump driven by LGATE1 without over discharging the output voltage.
19 LGATE1 Lower Gate Drive Output for SMPS1. LGATE1 swings between GND and VREG5.
Switch Node for SMPS1. PHASE1 is the internal lower supply rail for the UGATE1 high
20 PHASE1
side gate driver. PHASE1 is also the current sense input for the SMPS1.
21 UGATE1 Upper Gate Driver Output for SMPS1. UGATE1 swings between PHASE1 and BOOT1.
Boost Flying Capacitor Connection for SMPS1. Connect to an external capacitor
22 BOOT1
according to the typical application circuits.
23 PGOOD Power Good Output for Channel 1 and Channel 2. (Logical AND)
Bypass Pin for SMPS1. Connect to the SMPS1 output to bypass efficient power for
24 VOUT1
VREG5 pin. VOUT1 is also for the SMPS1 output soft-discharge.

Function Block Diagram

TONSEL SKIPSEL

BOOT1 BOOT2

UGATE1 UGATE2

PHASE1
http://www.DataSheet4U.net/

PHASE2
VREG5 VREG5

SMPS1 SMPS2
LGATE1 PWM Buck PWM Buck LGATE2
Controller Controller
VREG5
VREG5

VOUT2
FB1 FB2
ENTRIP1 ENTRIP2
PGOOD
EN Power-On
Sequence
Clear Fault Latch
GND
SW5 Threshold SW3 Threshold

VOUT1

Thermal
Shutdown

VREG5 VREG3

VREG5 REF VREG3

VIN

REF

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RT8205L/M
Absolute Maximum Ratings (Note 1)
z VIN, EN to GND ----------------------------------------------------------------------------------------------- −0.3V to 30V
z PHASEx to GND
DC ---------------------------------------------------------------------------------------------------------------- −0.3V to 30V
< 20ns ----------------------------------------------------------------------------------------------------------- −8V to 38V
z BOOTx to PHASEx ------------------------------------------------------------------------------------------ −0.3V to 6V
z ENTRIPx, SKIPSEL, TONSEL, PGOOD to GND ------------------------------------------------------ −0.3V to 6V
z VREG5, VREG3, FBx , VOUTx, SECFB, REF to GND ---------------------------------------------- −0.3V to 6V
z UGATEx to PHASEx

DC ---------------------------------------------------------------------------------------------------------------- −0.3V to (VREG5 + 0.3V)

< 20ns ----------------------------------------------------------------------------------------------------------- −5V to 7.5V
z LGATEx to GND

DC ---------------------------------------------------------------------------------------------------------------- −0.3V to (VREG5 + 0.3V)

< 20ns ----------------------------------------------------------------------------------------------------------- −2.5V to 7.5V
z Power Dissipation, PD @ TA = 25°C

WQFN-24L-4x4 ------------------------------------------------------------------------------------------------ 1.923W

z Package Thermal Resistance (Note 2)

WQFN-24L-4x4, θJA ------------------------------------------------------------------------------------------ 52°C/W

WQFN-24L-4x4, θJC ------------------------------------------------------------------------------------------ 7°C/W
z Lead Temperature (Soldering, 10 sec.) ------------------------------------------------------------------ 260°C
z Junction Temperature ---------------------------------------------------------------------------------------- 150°C
z Storage Temperature Range -------------------------------------------------------------------------------- −65°C to 150°C
z ESD Susceptibility (Note 3)

HBM (Human Body Mode) ---------------------------------------------------------------------------------- 2kV

http://www.DataSheet4U.net/

MM (Machine Mode) ----------------------------------------------------------------------------------------- 200V

Recommended Operating Conditions (Note 4)

z Supply Input Voltage, VIN ----------------------------------------------------------------------------------- 6V to 25V
z Junction Temperature Range ------------------------------------------------------------------------------- −40°C to 125°C
z Ambient Temperature Range ------------------------------------------------------------------------------- −40°C to 85°C

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 RT8205L/M
Electrical Characteristics
(VIN = 12V, VEN = 5V, VENTRIP1 = VENTRIP2 = 2V, No Load, TA = 25°C, unless otherwise specified)
Parameter Symbol Test Conditions Min Typ Max Unit
Input Supply

VIN Standby Current IVIN_SBY VIN = 6V to 25V, ENTRIPx = GND -- 200 -- μA

VIN Shutdown Supply VIN = 6V to 25V,

IVIN_SHDN -- 20 40 μA
Current ENTRIPx = EN = GND
Both SMPS On, VFBx = 2.1V,
Quiescent Power PVIN
SKIPSEL = REF, VOUT1 = 5V, -- 5 7 mW
Consumption +PPVCC
VOUT2 = 3.3V (Note 5)
SMPS Output and FB Voltage
DEM Mode 1.975 2 2.025
FBx Voltage VFBx PWM Mode (Note 6) -- 2 -- V
Ultrasonic Mode -- 2.032 --
SECFB Voltage VSECFB 1.92 2 2.08 V
Output Voltage Adjust
VOUTx SMPS1, SMPS2 2 -- 5.5 V
Range
VOUTx Discharge
VOUTx = 0.5V, VENTRIPx = 0V 10 45 -- mA
Current
On-Time
VOUT1 = 5.05V (200kHz) 1895 2105 2315
TONSEL = GND
VOUT2 = 3.33V (250kHz) 999 1110 1221
VOUT1 = 5.05V (300kHz)
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1227 1403 1579

On-Time Pulse Width tON TONSEL = REF ns
VOUT2 = 3.33V (375kHz) 647 740 833

TONSEL = VOUT1 = 5.05V (400kHz) 895 1052 1209

VREG5 VOUT2 = 3.33V (500kHz) 475 555 635
Minimum Off-Time tOFF FBx = 1.9V 200 300 400 ns
Ultrasonic Mode
SKIPSEL = VREG5 or VREG3 22 33 -- kHz
Frequency
Soft-Start
Soft-Start Time tSSx Internal Soft-Start -- 2 -- ms
Current Sense
ENTRIPx Source
IENTRIPx VENTRIPx = 0.9V 9.4 10 10.6 μA
Current
ENTRIPx Current
Temperature TCIENTRIPx In Comparison with 25°C (Note 6) -- 4700 -- ppm/°C
Coefficient
ENTRIPx Adjustment
VENTRIPx = I ENTRIPx x RENTRIPx 0.515 -- 3 V
Range
Current Limit
GND − PHASEx, VENTRIPx = 2V 180 200 220 mV
Threshold
Zero-Current
GND − PHASEx in DEM -- 3 -- mV
Threshold

To be continued
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RT8205L/M
Parameter Symbol Test Conditions Min Typ Max Unit
Internal Regulator and Reference
VOUT1 = GND, IVREG5 < 100mA 4.8 5 5.2
VOUT1 = GND, 6.5V < VIN < 25V,
VREG5 Output Voltage VVREG5 4.75 5 5.25 V
IVREG5 < 100mA
VOUT1 = GND, 5.5V < VIN < 25V,
4.75 5 5.25
IVREG5 < 50mA
VOUT2 = GND, IVREG3 < 100mA 3.2 3.33 3.46
VOUT2 = GND, 6.5V < VIN < 25V,
3.13 3.33 3.5
VREG3 Output Voltage VVREG3 IVREG3 < 100mA V
VOUT2 = GND, 5.5V < VIN < 25V,
3.13 3.33 3.5
IVREG3 < 50mA
VREG5 Output Current IVREG5 VVREG5 = 4.5V, VOUT1 = GND 100 175 250 mA
VREG3 Output Current IVREG3 VVREG3 = 3V, V OUT2 = GND 100 175 250 mA
VREG5 Switchover VOUT1 Rising Edge 4.6 4.75 4.9
VSW5 V
Threshold to VOUT1 VOUT1 Falling Edge 4.3 4.4 4.5
VREG3 Switchover VOUT2 Rising Edge 2.975 3.125 3.25
VSW3 V
Threshold to VOUT2 VOUT2 Falling Edge 2.775 2.875 2.975
VREGx Switchover Equivalent
R SWx VREGx to VOUTx, 10mA -- 1.5 3 Ω
Resistance
REF Output Voltage V REF No External Load 1.98 2 2.02 V
REF Load Regulation 0 < ILOAD < 100μA -- 10 -- mV
REF Sink Current REF in Regulation
http://www.DataSheet4U.net/
5 -- -- μA
UVLO
VREG5 Under Voltage Rising Edge -- 4.20 4.35
V
Lockout Threshold Falling Edge 3.7 3.9 4.1
VREG3 Under Voltage
SMPSx off -- 2.5 -- V
Lockout Threshold
Power Good
PGOOD Detect, FBx Falling Edge 82 85 88
PGOOD Threshold Hysteresis, Rising Edge with SS %
-- 6 --
Delay Time
PGOOD Propagation Delay Falling Edge, 50mV Overdrive -- 10 -- μs
PGOOD Leakage Current High State, Forced to 5.5V -- -- 1 μA
PGOOD Output Low Voltage ISINK = 4mA -- -- 0.3 V
Fault Detection
Over Voltage Protection Trip
V FB_OVP OVP Detect, FBx Rising Edge 109 112 116 %
Threshold
Over Voltage Protection
FBx = 2.35V -- 5 -- μs
Propagation Delay
Under Voltage Protection Trip
V FB_UVP UVP Detect, FBx Falling Edge 49 52 56 %
Threshold
UVP Shutdown Blanking Time tSHDN_UVP From ENTRIPx Enable -- 5 -- ms

To be continued
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 RT8205L/M
Parameter Symbol Test Conditions Min Typ Max Unit
Thermal Shutdown
Thermal Shutdown TSHDN -- 150 -- °C
Thermal Shutdown
-- 10 -- °C
Hysteresis
Logic Input
Low Level (PWM Mode) -- -- 0.8
SKIPSEL Input Voltage REF Level (DEM Mode) 1.8 -- 2.3 V
High Level (Ultrasonic Mode) 2.7 -- --
Low Level (SMPS Off) -- -- 0.25
ENTRIPx Input Voltage V ENTRIPx On Level (SMPS On) 0.515 -- 3 V
High Level (SMPS Off) 4.5 -- --
EN Threshold Logic-High VIH 1 -- --
V
Voltage Logic-Low VIL -- -- 0.4
EN Voltage VEN Floating, Default Enable 2.4 3.3 4.2 V
VEN = 0.2V, Source 1.5 3 5
EN Current IEN μA
VEN = 5V, Sink -- 3 8
VOUT1 / VOUT2 = 200kHz / 250kHz -- -- 0.8
TONSEL Setting Voltage VOUT1 / VOUT2 = 300kHz / 375kHz 1.8 -- 2.3 V
VOUT1 / VOUT2 = 400kHz / 500kHz 2.7 -- --
VTONSEL, VSKIPSEL = 0V or 5V −1 -- 1
Input Leakage Current μA
http://www.DataSheet4U.net/

VSECFB = 0V or 5V −1 -- 1
Internal BOOT Switch
Internal Boost Switch
VREG5 to BOOTx, 10mA -- 40 80 Ω
On-Resistance
Power MOSFET Drivers
UGATEx, High State,
-- 4 8
BOOTx to PHASEx Forced to 5V
UGATEx On-Resistance Ω
UGATEx, Low State,
-- 1.5 4
BOOTx to PHASEx Forced to 5V
LGATEx, High State -- 4 8
LGATEx On-Resistance Ω
LGATEx, Low State -- 1.5 4
LGATEx Rising -- 30 --
Dead Time ns
UGATEx Rising -- 40 --

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RT8205L/M
Note 1. Stresses listed as the above “Absolute Maximum Ratings” may cause permanent damage to the device. These are for
stress ratings. Functional operation of the device at these or any other conditions beyond those indicated in the
operational sections of the specifications is not implied. Exposure to absolute maximum rating conditions for extended
periods may remain possibility to affect device reliability.
Note 2. θJA is measured in natural convection at TA = 25°C on a high effective four layers thermal conductivity four-layer test
board of JEDEC 51-7 thermal measurement standard. The measurement case position of θJC is on the exposed pad
of the package.
Note 3. Devices are ESD sensitive. Handling precaution is recommended.
Note 4. The device is not guaranteed to function outside its operating conditions.
Note 5. PVIN + PVREG5
Note 6. Guaranteed by Design.

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 RT8205L/M
Typical Operating Characteristics
VOUT1 Efficiency vs. Load Current VOUT1 Efficiency vs. Load Current
100 100
90 DEM Mode 90 DEM Mode
80 80
70 70
Efficiency (%)

Efficiency (%)
PWM Mode
60 60 PWM Mode
Ultrasonic Mode Ultrasonic Mode
50 50
40 40
30 30
20 20 VIN = 12V, TONSEL = GND,
10 VIN = 8V, TONSEL = GND, VENTRIP1 = 1.5V, 10 VENTRIP1 = 1.5V, ENTRIP2 = GND,
ENTRIP2 = GND, EN = FLOATING EN = FLOATING
0 0
0.001 0.01 0.1 1 10 0.001 0.01 0.1 1 10
Load Current (A) Load Current (A)

VOUT1 Efficiency vs. Load Current VOUT2 Efficiency vs. Load Current
100 100
90 90
DEM Mode
80 80 DEM Mode
70 70
Efficiency (%)
Efficiency (%)

60 60
50 PWM Mode 50 PWM Mode
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40 40 Ultrasonic Mode
Ultrasonic Mode
30 30
20 20
VIN = 20V, TONSEL = GND, VIN = 8V, TONSEL = GND,
10 VENTRIP1 = 1.5V, ENTRIP2 = GND, 10 ENTRIP1 = GND, VENTRIP2 = 1.5V,
EN = FLOATING EN = FLOATING
0 0
0.001 0.01 0.1 1 10 0.001 0.01 0.1 1 10
Load Current (A) Load Current (A)

VOUT2 Efficiency vs. Load Current VOUT2 Efficiency vs. Load Current
100 100

90 90
80 80
70 DEM Mode 70 DEM Mode
Efficiency (%)

Efficiency (%)

60 60
PWM Mode Ultrasonic
50 50 PWM Mode
Mode
40 40
30
Ultrasonic Mode 30
20
VIN = 12V, TONSEL = GND, 20
10 ENTRIP1 = GND, VENTRIP2 = 1.5V, VIN = 20V, TONSEL = GND,
EN = FLOATING 10 ENTRIP1 = GND, VENTRIP2 = 1.5V,
0 EN = FLOATING
0
0.001 0.01 0.1 1 10
0.001 0.01 0.1 1 10
Load Current (A)
Load Current (A)

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RT8205L/M

VOUT1 Switching Frequency vs. Load Current VOUT1 Switching Frequency vs. Load Current
220 220
200 PWM Mode 200 PWM Mode

Switching Frequency (kHz)1

Switching Frequency (kHz)1

180 180
160 160
140 140
120 120
100 100
80 80
60
VIN = 8V, VIN = 12V,
60
TONSEL = GND, TONSEL = GND,
40 Ultrasonic Mode EN = FLOATING, 40 Ultrasonic Mode EN = FLOATING,
VENTRIP1 = 1.5V, VENTRIP1 = 1.5V,
20 20
DEM Mode ENTRIP2 = GND DEM Mode ENTRIP2 = GND
0 0
0.001 0.01 0.1 1 10 0.001 0.01 0.1 1 10
Load Current (A) Load Current (A)

VOUT1 Switching Frequency vs. Load Current VOUT2 Switching Frequency vs. Load Current
220 280
200 PWM Mode 260 PWM Mode
Switching Frequency (kHz)1

Switching Frequency (kHz)1

240
180
220
160 200
140 180
160
120
140
100 http://www.DataSheet4U.net/

120
80 100
VIN = 20V, 80 VIN = 8V,
60
TONSEL = GND, TONSEL = GND,
Ultrasonic Mode 60
40 EN = FLOATING, Ultrasonic Mode EN = FLOATING,
40 ENTRIP1 = GND,
20 VENTRIP1 = 1.5V,
DEM Mode 20 DEM Mode VENTRIP2 = 1.5V
ENTRIP2 = GND
0 0
0.001 0.01 0.1 1 10 0.001 0.01 0.1 1 10
Load Current (A) Load Current (A)

VOUT2 Switching Frequency vs. Load Current VOUT2 Switching Frequency vs. Load Current
280 280
260 PWM Mode 260 PWM Mode
Switching Frequency (kHz) 1

Switching Frequency (kHz) 1

240 240
220 220
200 200
180 180
160 160
140 140
120 120
100 100
80 VIN = 12V, 80 VIN = 20V,
TONSEL = GND, TONSEL = GND,
60 60
Ultrasonic Mode EN = FLOATING, Ultrasonic Mode EN = FLOATING,
40 ENTRIP1 = GND, 40 ENTRIP1 = GND,
20 DEM Mode VENTRIP2 = 1.5V 20 DEM Mode VENTRIP2 = 1.5V
0 0
0.001 0.01 0.1 1 10 0.001 0.01 0.1 1 10
Load Current (A) Load Current (A)

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 RT8205L/M

VOUT1 Output Voltage vs. Load Current VOUT2 Output Voltage vs. Load Current
5.090 3.446
VIN = 12V, VIN = 12V,
5.084 3.440
Ultrasonic Mode TONSEL = GND, TONSEL = GND,
5.078 Ultrasonic Mode EN = FLOATING,
EN = FLOATING, 3.434
5.072 VENTRIP1 = 1.5V, ENTRIP2 = GND,
5.066
Output Voltage (V)

Output Voltage (V)

ENTRIP2 = GND 3.428 VENTRIP1 = 1.5V
5.060
3.422
5.054
5.048 3.416
5.042 3.410
5.036 PWM Mode
3.404
5.030
5.024 PWM Mode 3.398
5.018 3.392
5.012 DEM Mode
5.006 DEM Mode 3.386
5.000 3.380
0.001 0.01 0.1 1 10 0.001 0.01 0.1 1 10
Load Current (A) Load Current (A)

VREG5 Output Voltage vs. Output Current VREG3 Output Voltage vs. Output Current
5.006 3.358

5.002
3.354
4.998
Output Voltage (V)

Output Voltage (V)

3.350
4.994

4.990 3.346

4.986 http://www.DataSheet4U.net/
3.342
4.982
3.338
4.978
3.334
4.974 VIN = 12V, ENTRIP1 = ENTRIP2 = GND, VIN = 12V, ENTRIP1 = ENTRIP2 = GND,
EN = FLOATING, TONSEL = GND EN = FLOATING, TONSEL = GND
4.970 3.330
0 10 20 30 40 50 60 70 80 90 100 0 10 20 30 40 50 60 70
Output Current (mA) Output Current (mA)

Reference Voltage vs. Output Current Battery Current vs. Input Voltage
2.0080 100.0
PWM Mode
2.0072
2.0064
Reference Voltage (V)

Battery Current (mA)

2.0056
10.0
2.0048
2.0040 Ultrasonic Mode

2.0032
1.0
2.0024
DEM Mode
2.0016
2.0008 VIN = 12V, ENTRIP1 = ENTRIP2 = GND, VENTRIP1 = VENTRIP2 = 0.91V,
EN = FLOATING, TONSEL = GND TONSEL = GND, EN = FLOATING
2.0000 0.1
-10 0 10 20 30 40 50 60 70 80 90 100 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25
Output Current (μA) Input Voltage (V)

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RT8205L/M

Standby Input Current vs. Input Voltage Shutdown Input Current vs. Input Voltage
250 22
249

Shutdown Input Current (μA)1

Standby Input Current (μA)1

20
248
247 18

246
16
245
14
244
243 12
242
ENTRIP1 = ENTRIP2 = GND, 10
241
EN = FLOATING, No Load ENTRIP1 = ENTRIP2 = EN = GND, No Load
240 8
7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 7 9 11 13 15 17 19 21 23 25
Input Voltage (V) Input Voltage (V)

Reference Voltage vs. Temperature VREG5, VREG3 and REF Start Up

2.011
ENTRIP1 = ENTRIP2 = GND, EN = FLOATING
2.008
VREG5
Reference Voltage (V)

2.005
(5V/Div)
2.002

1.999 VREG3
1.996
(2V/Div)
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1.993
REF
1.990 (2V/Div)
VIN = 12V, ENTRIP1 = ENTRIP2 = GND, EN
1.987
EN = FLOATING, TONSEL = GND (5V/Div) VIN = 12V, TONSEL = GND, No Load
1.984
-50 -25 0 25 50 75 100 125 Time (400μs/Div)
Temperature (°C)

VOUT1 Start Up VOUT2 Start Up

VOUT1
(1V/Div)
PGOOD VOUT2
(5V/Div) (1V/Div)
PGOOD
(5V/Div)
ENTRIP1
VENTRIP1 = 1.5V, ENTRIP2 = GND, ENTRIP1 = GND, VENTRIP2 = 1.5V,
(1V/Div) EN = FLOATING, VIN = 12V,
ENTRIP2 EN = FLOATING, VIN = 12V,
TONSEL = GND, SKIPSEL = GND, TONSEL = GND, SKIPSEL = GND,
No Load (1V/Div) No Load

Time (1ms/Div) Time (1ms/Div)

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 RT8205L/M

CP Start Up VOUT1 Delay-Start

VOUT1
(5V/Div)

CP VOUT1
(10V/Div) (2V/Div)
UGATE VOUT2
(20V/Div) (1V/Div)
LGATE ENTRIP1
(10V/Div) VENTRIP1 = VENTRIP2 = 1.5V, EN = FLOATING, (2V/Div)
VIN = 12V, TONSEL = GND,
VIN = 12V, TONSEL = GND, SKIPSEL = REF, ENTRIP2 EN = FLOATING, SKIPSEL = GND,
No Load (2V/Div) No Load

Time (2ms/Div) Time (2ms/Div)

VOUT2 Delay-Start Power Off from ENTRIP1

VIN = 12V, TONSEL = GND,
SKIPSEL = GND,
EN = FLOATING

VOUT1
VOUT1
(2V/Div)
(2V/Div)
PGOOD
(5V/Div)
VOUT2 ENTRIP1
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(1V/Div) (2V/Div)
ENTRIP1 No Load on VOUT1, VOUT2,
(2V/Div) VREG5, VREG3 and REF
ENTRIP2 VIN = 12V, TONSEL = GND, LGATE1
EN = FLOATING, SKIPSEL = GND, (5V/Div)
(2V/Div) No Load

Time (2ms/Div) Time (4ms/Div)

Power Off from ENTRIP2 VOUT1 PWM-Mode Load Transient Response

VOUT1_ac
(50mV/Div)
VOUT2
(2V/Div) Inductor
PGOOD Current
(5V/Div) (5A/Div)
ENTRIP2
(2V/Div)
UGATE1
(20V/Div) VIN = 12V, TONSEL = GND, SKIPSEL = GND
LGATE2
(5V/Div) VIN = 12V, TONSEL = GND, SKIPSEL = GND, LGATE1
EN = FLOATING, No Load on VOUT1, VOUT2,
VREG5, VREG3 and REF
(5V/Div) EN = FLOATING, IOUT1 = 0A to 6A

Time (4ms/Div) Time (20μs/Div)

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RT8205L/M

VOUT2 PWM-Mode Load Transient Response OVP

VOUT2_ac
(50mV/Div)

Inductor
Current VOUT1
(5A/Div) (2V/Div)

UGATE VOUT2
(20V/Div) (2V/Div)
VIN = 12V, TONSEL = GND, SKIPSEL = GND
PGOOD
(5V/Div)
LGATE VIN = 12V, TONSEL = GND, SKIPSEL = REF,
(5V/Div) EN = FLOATING, IOUT2 = 0A to 6A EN = FLOATING, No Load

Time (20μs/Div) Time (4ms/Div)

UVP
VIN = 12V,
TONSEL = GND,
SKIPSEL = GND,
EN = FLOATING,
No Load
VOUT1
(2V/Div)
PGOOD
(5V/Div) http://www.DataSheet4U.net/

UGATE
(20V/Div)

LGATE
(5V/Div)

Time (100μs/Div)

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 RT8205L/M
Application Information
The RT8205L/M is a dual, Mach ResponseTM DRVTM dual and output voltage into the on-time one shot timer. The
ramp valley mode synchronous buck controller. The high side switch on-time is inversely proportional to the
controller is designed for low-voltage power supplies for input voltage as measured by VIN, and proportional to the
notebook computers. Richtek's Mach Response TM output voltage. There are two benefits of a constant
technology is specifically designed for providing 100ns switching frequency. First, the frequency can be selected
“instant-on” response to load steps while maintaining a to avoid noise-sensitive regions such as the 455kHz IF
relatively constant operating frequency and inductor band. Second, the inductor ripple-current operating point
operating point over a wide range of input voltages. The remains relatively constant, resulting in easy design
topology circumvents the poor load-transient timing methodology and predictable output voltage ripple.
problems of fixed-frequency current-mode PWMs while Frequency for the 3V SMPS is set at 1.25 times higher
avoiding the problems caused by widely varying switching than the frequency for 5V SMPS. This is done to prevent
frequencies in conventional constant-on-time and constant- audio frequency “beating” between the two sides, which
off-time PWM schemes. The DRV TM mode PWM switches asynchronously for each side. The frequencies
modulator is specifically designed to have better noise are set by the TONSEL pin connection as shown in Table
immunity for such a dual output application. The RT8205L/ 1. The on-time is given by :
M includes 5V (VREG5) and 3.3V (VREG3) linear t ON = K × (VOUT / VIN )
regulators. VREG5 linear regulator can step down the
where “K” is set by the TONSEL pin connection (Table
battery voltage to supply both internal circuitry and gate
1).
drivers. The synchronous-switch gate drivers are directly
powered from VREG5. When VOUT1 voltage is above The on-time guaranteed in the Electrical Characteristics
4.66V, an automatic circuit will switch the power of the table is influenced by switching delays in the external
device from VREG5 linear regulator to VOUT1. high side power MOSFET. Two external factors that
influence switching frequency accuracy are resistive drops
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PWM Operation in the two conduction loops (including inductor and PC

The Mach ResponseTM DRVTM mode controller relies on board resistance) and the dead time effect. These effects
the output filter capacitor's Effective Series Resistance are the largest contributors to the change frequency with
(ESR) to act as a current-sense resistor, so the output changing load current. The dead time effect increases the
ripple voltage provides the PWM ramp signal. Referring to effective on-time by reducing the switching frequency. It
the RT8205L/M's function block diagram, the synchronous occurs only in PWM mode (SKIPSEL = GND) when the
high side MOSFET will be turned on at the beginning of inductor current reverses at light or negative load currents.
each cycle. After the internal one-shot timer expires, the With reversed inductor current, the inductor's EMF causes
MOSFET will be turned off. The pulse width of this one PHASEx to go high earlier than normal, thus extending
shot is determined by the converter's input voltage and the on-time by a period equal to the low-to-high dead time.
the output voltage to keep the frequency fairly constant For loads above the critical conduction point, the actual
over the input voltage range. Another one-shot sets a switching frequency is :
minimum off-time (300ns typ.). The on-time one-shot will f = (VOUT + VDROP1) / (t ON × (VIN + VDROP1 − VDROP2 ))
be triggered if the error comparator is high, the low side
switch current is below the current limit threshold, and where VDROP1 is the sum of the parasitic voltage drops in
the minimum off-time one-shot has timed out. the inductor discharge path, which includes the
synchronous rectifier, inductor, and PC board resistances.
PWM Frequency and On-Time Control VDROP2 is the sum of the resistances in the charging path;
The Mach ResponseTM control architecture runs with and tON is the on-time.
pseudo constant frequency by feed forwarding the input

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RT8205L/M
Table 1. TONSEL Connection and Switching Frequency
SMPS 1 SMPS 1 SMPS 2 SMPS 2 Approximate K-Factor
TONSEL
K-Factor (μs) Frequency (kHz) K-Factor (μs) Frequency (kHz) Error (%)
GND 5 200 4 250 ±10
REF 3.33 300 2.67 375 ±10
VREG5 or
2.5 400 2 500 ±10
VREG3

Operation Mode Selection (SKIPSEL) (VIN − VOUT )

ILOAD(SKIP) ≈ × t ON
The RT8205L/M supports three operation modes: Diode- 2L
Emulation Mode, Ultrasonic Mode, and Forced-CCM where tON is the On-time.
Mode. User can set operation mode via the SKIPSEL pin.
The switching waveforms may appear noisy and
Diode-Emulation Mode (SKIPSEL = REF) asynchronous when light loading causes Diode-Emulation
Mode operation. However, this is normal and results in
In Diode-Emulation Mode, the RT8205L/M automatically
high efficiency. Trade offs in PFM noise vs. light load
reduces switching frequency at light load conditions to
efficiency is made by varying the inductor value. Generally,
maintain high efficiency. This reduction of frequency is
low inductor values produce a broader efficiency vs. load
achieved smoothly. As the output current decreases from
curve, while higher values result in higher full load efficiency
heavy load condition, the inductor current is also reduced
(assuming that the coil resistance remains fixed) and less
and eventually comes to the point when its valley touches
output voltage ripple. Penalties for using higher inductor
zero current, which is the boundary between continuous
values include larger physical size and degraded load
conduction and discontinuous conduction modes. By
transient response (especially at low input voltage levels).
emulating the behavior of diodes, the low side MOSFET
allows only partial negative current when the inductor free
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Ultrasonic Mode (SKIPSEL = VREG5 or VREG3)

wheeling current becomes negative. As the load current
The RT8205L/M activates an unique Diode-Emulation Mode
is further decreased, it takes longer and longer to discharge
with a minimum switching frequency of 25kHz, called the
the output capacitor to the level that requires the next
Ultrasonic Mode. The Ultrasonic Mode avoids audio-
“ON” cycle. The on-time is kept the same as that in the
frequency modulation that would otherwise be present
heavy-load condition. In reverse, when the output current
when a lightly loaded controller automatically skips
increases from light load to heavy load, the switching
pulses. In Ultrasonic Mode, the high side switch gate driver
frequency increases to the preset value as the inductor
signal is ORed with an internal oscillator (>25kHz). Once
current reaches the continuous conduction. The transition
the internal oscillator is triggered, the controller enters
load point to the light load operation as follows (Figure 1) :
constant off-time control. When output voltage reaches
the setting peak threshold, the controller turns on the low
IL side MOSFET until the controller detects that the inductor
Slope = (VIN -VOUT) / L
IL, PEAK current has dropped below the zero crossing threshold.
The internal circuitry provides a constant off-time control,
and it is effective to regulate the output voltage under light
ILoad = IL, PEAK / 2 load condition.

Forced CCM Mode (SKIPSEL = GND)

0
t The low noise, Forced CCM mode (SKIPSEL = GND)
tON
disables the zero crossing comparator, which controls
Figure 1. Boundary Condition of CCM/DEM the low side switch on-time. This causes the low side

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 RT8205L/M
gate driver waveform to become the complement of the Therefore, the exact current limit characteristic and
high side gate driver waveform. This in turn causes the maximum load capability are functions of the sense
inductor current to reverse at light loads as the PWM loop resistance, inductor value, and battery and output voltage.
to maintain a duty ratio of VOUT/VIN. The benefit of forced IL
CCM mode is to keep the switching frequency fairly
IL, peak
constant, but it comes at a cost. The no-load battery
current can be from 10mA to 40mA, depending on the ILoad
external MOSFETs.
ILIM

Reference and Linear Regulators (REF, VREGx)

The 2V reference (REF) is accurate within ±1% over the
t
0
entire operating temperature range, making REF useful
as a precision system reference. Bypass REF to GND Figure 2. “ Valley” Current Limit
with a minimum 0.22μF ceramic capacitor. REF can supply The RT8205L/M uses the on resistance of the synchronous
up to 100μA for external loads. Loading REF reduces the rectifier as the current sense element and supports
VOUTx output voltage slightly because of the reference temperature compensated MOSFET RDS(ON) sensing. The
load regulation error. RILIMx resistor between the ENTRIPx pin and GND sets
The RT8205L/M includes 5V (VREG5) and 3.3V (VREG3) the current limit threshold. The resistor RILIMx is connected
linear regulators. The VREG5 regulator supplies a total of to a current source from ENTRIPx, which is typically10μA
100mA for internal and external loads, including the at room temperature. The current source has a 4700ppm/
MOSFET gate driver and PWM controller. The VREG3 °C temperature slope to compensate the temperature
regulator supplies up to 100mA for external loads. Bypass dependency of the RDS(ON). When the voltage drop across
VREG5 and VREG3 with a minimum 4.7μF ceramic the sense resistor or low side MOSFET equals 1/10 the
capacitor. voltage across the RILIMx resistor, positive current limit
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will be activated. The high side MOSFET will not be turned

When the 5V main output voltage is above the VREG5
on until the voltage drop across the MOSFET falls below
switchover threshold (4.75V), an internal 1.5Ω P- MOSFET
1/10 the voltage across the RILIMx resistor.
switch connects VOUT1 to VREG5, while simultaneously
shutting down the VREG5 linear regulator. Similarly, when Choose a current limit resistor by following equation :
the 3.3V main output voltage is above the VREG3 VILIMx = (RILIMx × 10μ A)/10 = IILIMx × RDS(ON)
switchover threshold (3.125V), an internal 1.5Ω
RILIMx = (IILIMx × RDS(ON) ) × 10 / 10μ A
P-MOSFET switch connects VOUT2 to VREG3, while
simultaneously shutting down the VREG3 linear regulator. Carefully observe the PC board layout guidelines to
It can decrease the power dissipation from the same ensures that noise and DC errors do not corrupt the current
battery, because the converted efficiency of SMPS is sense signal at PHASEx and GND. Mount or place the IC
better than the converted efficiency of the linear regulator. close to the low side MOSFET.

Current Limit Setting (ENTRIPx) Charge Pump (SECFB)

The RT8205L/M has a cycle-by-cycle current limit control. The external 14V charge pump is driven by LGATEx (Figure
The current limit circuit employs an unique “Valley” current 3). When LGATEx is low, C1 will be charged by D1 from
sensing algorithm. If the magnitude of the current sense VOUT1. C1 voltage is equal to VOUT1 minus a diode drop.
signal at PHASEx is above the current limit threshold, When LGATEx transitions to high, the charges from C1
the PWM is not allowed to initiate a new cycle (Figure 2). will transfer to C2 through D2 and charge it to VLGATEX plus
The actual peak current is greater than the current limit VC1. As LGATEx transitions low on the next cycle, C2
threshold by an amount equal to the inductor ripple current. will charge C3 to its voltage minus a diode drop through

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RT8205L/M
D3. Finally, C3 charges C4 through D4 when LGATEx The low side driver is designed to drive high current, low
switches to high. So, VCP voltage is : RDS(ON) N-MOSFET(s). The internal pull down transistor
VCP = VOUT1+ 2 × VLGATEX − 4 × VD that drives LGATEx low is robust, with a 1.5Ω typical on
resistance. A 5V bias voltage is delivered from the VREG5
where VLGATEX is the peak voltage of LGATEx driver and is
supply. The instantaneous drive current is supplied by an
equal to the VREG5; VD is the forward diode dropped
input capacitor connected between VREG5 and GND.
across the Schottky.
For high current applications, some combinations of high
SECFB in the RT8205M is used to monitor the charge
and low side MOSFETs might be encountered that will
pump through the resistive divider (Figure 3) to generate
cause excessive gate drain coupling, which can lead to
approximately 14V DC voltage and the clock driver uses
efficiency killing, EMI producing shoot through currents.
VOUT1 as its power supply. In the event when SECFB
This can be remedied by adding a resistor in series with
drops below its feedback threshold, an ultrasonic pulse
BOOTx, which increases the turn-on time of the high side
will occur to refresh the charge pump driven by LGATEx.
MOSFET without degrading the turn-off time (Figure 4).
In the event of an overload on charge pump where SECFB
VIN
can not reach more than its feedback threshold, the
controller will enter the ultrasonic mode. Special care RBOOT
should be taken to ensure enough normal ripple voltage BOOTx

on each cycle as to prevent charge pump shutdown.

UGATEx
Reducing the charge pump decoupling capacitor and
placing a small ceramic capacitor (47 pF to 220pF) (CF of PHASEx

Figure 3) in parallel with the upper leg of the SECFB

resistor feedback network (RCP1 of Figure 3) will also
Figure 4. Reducing the UGATEx Rise Time
increase the robustness of the charge pump.
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Soft-Start
SECFB RCP2
LGATE1 The RT8205L/M provides internal soft-start function to
CF
RCP1
prevent large inrush current and output voltage overshoot
C1 C3
D2 D3 D4 when the converter starts up. The soft-start (SS)
CP
automatically begins once the chip is enabled. During soft-
D1 C2 C4
start, the voltage is clamped to the ramping of internal
VOUT1 reference voltage which is compared with FBx signal. The
Figure 3. Charge Pump Circuit Connected to SECFB typical soft-start duration is 2ms. An unique PWM duty
limit control that prevents output over voltage during soft-
MOSFET Gate Driver (UGATEx, LGATEx)
start period is designed specifically for FBx floating.
The high side driver is designed to drive high current, low
RDS(ON) N-MOSFET(s). When configured as a floating driver, UVLO Protection
a 5V bias voltage is delivered from the VREG5 supply. The RT8205L/M features VREG5 under voltage lockout
The average drive current is calculated by the gate charge protection (UVLO). When the VREG5 voltage is lower than
at V GS = 5V times the switching frequency. The 3.9V (typ.) and the VREG3 voltage is lower than 2.5V
instantaneous drive current is supplied by the flying (typ.), both switch power supplies are shut off. This is
capacitor between the BOOTx and PHASEx pins. A dead non-latch protection.
time to prevent shoot through is internally generated
between the high side MOSFET off to, the low side Power Good Output (PGOOD)
MOSFET on, and the low side MOSFET off to the high PGOOD is an open-drain type output and requires a pull-
side MOSFET on. up resistor. PGOOD is actively held low in soft-start,

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 RT8205L/M
standby, and shutdown. It is released when both output supplied from VOUTx, while the input voltage on VIN and
voltages are above 91% of the nominal regulation point. the drawing current from VREGx are too high. Even if
The PGOOD goes low if either output turns off or is 15% VREGx is supplied from VOUTx, large power dissipation
below its nominal regulator point. on automatic switches caused by overloading VREGx,
which may also result in thermal shutdown.
Output Over Voltage Protection (OVP)
The output voltage can be continuously monitored for over Discharge Mode (Soft-Discharge)
voltage. If the output voltage exceeds 12% of its set voltage When ENTRIPx is low and a transition to standby or
threshold, the over voltage protection is triggered and the shutdown mode occurs, or the output under voltage fault
LGATEx low side gate drivers are forced high. This latch is set, the output discharge mode will be triggered.
activates the low side MOSFET switch, which rapidly During discharge mode, the output capacitors' residual
discharges the output capacitor and pulls the input voltage charge will be discharge to GND through an internal switch.
downward.
Shutdown Mode
The RT8205L/M is latched once OVP is triggered and can
The RT8205L/M SMPS1, SMPS2, VREG3 and VREG5
only be released by toggling EN, ENTRIPx or cycling VIN.
have independent enabling control. Drive EN, ENTRIP1
There is a 5μs delay built into the over voltage protection
and ENTRIP2 below the precise input falling edge trip level
circuit to prevent false alarm.
to place the RT8205L/M in its low power shutdown state.
Note that the latching LGATEx high causes the output The RT8205L/M consumes only 20μA of input current while
voltage to dip slightly negative when energy has been in shutdown. When shutdown mode is activated, the
previously stored in the LC tank circuit. For loads that reference turns off. The accurate 0.4V falling edge threshold
cannot tolerate a negative voltage, place a power Schottky on the EN pin can be used to detect a specific analog
diode across the output to act as a reverse polarity clamp. voltage level as well as to shutdown the device. Once in
If the over voltage condition is caused by a short in the shutdown, the 1V rising edge threshold activates, providing
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high side switch, completely turning on the low side sufficient hysteresis for most applications.
MOSFET can create an electrical short between the
battery and GND, which will blow the fuse and disconnect Power Up Sequencing and On/Off Controls
the battery from the output. (ENTRIPx)
ENTRIP1 and ENTRIP2 control the SMPS power up
Output Under Voltage Protection (UVP) sequencing. When the RT8205L/M is in single channel
The output voltage can be continuously monitored for under mode, ENTRIP1 or ENTRIP2 enables the respective
voltage protection. If the output is less than 52% of its set outputs when ENTRIPx voltage rises above 0.515V.
voltage threshold, under voltage protection will be triggered, Since current source form ENTRIPx has 4700ppm/°C
and then both UGATEx and LGATEx gate drivers will be temperature slope, please make sure that ENTRIPx voltage
forced low. The UVP will be ignored for at least 5ms (typ.) is high enough to enable the respective output in low
after start up or a rising edge on ENTRIPx. Toggle ENTRIPx temperature application.
or cycle VIN to reset the UVP fault latch and restart the
If ENTRIPx pin becomes higher than the enable threshold
controller.
voltage while another channel is starting up, soft-start is
Thermal Protection postponed until the other channel's soft-start has
The RT8205L/M features thermal shutdown protection to completed. If both ENTRIP1 and ENTRIP2 become higher
prevent overheat damage to the device. Thermal shutdown than the enable threshold voltage simultaneously (within
occurs when the die temperature exceeds 150°C. All 60μs), both channels will be start up simultaneously. The
internal circuitry is inactive during thermal shutdown. The timing diagrams of the power sequence is shown below
RT8205L/M triggers thermal shutdown if VREGx is not (Figure 5).

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RT8205L/M

< 60µs > 60µs

0.515V VENTRIPx 0.515V

VENTRIPx

0.515V 0.515V
VENTRIPy VENTRIPy

VOUTx VOUTx

VOUTy VOUTy ≈2ms

(a). Start-Up at the Same Time (b). Delay Start Mode

Figure 5. Time Diagrams of Power Sequence

Table 2. Operation Mode Truth Table

Mode Condition Comment

Transitions to discharge mode after a VIN POR and after
Power UP VREGX < UVLO threshold REF becomes valid. VREG5, VREG3, and REF remain
active.
EN = high, VOUT1 or VOUT2
RUN Normal Operation.
enabled
Over Voltage Either output > 111% of the nominal LGATEx is forced high. VREG3, VREG5 and REF active.
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Protection level. Exited by VIN POR or by toggling EN, ENTRIPx

Under Either output < 52% of the nominal Both UGATEx and LGATEx are forced low and enter
Voltage level after 3ms time out expires and discharge mode. VREG3, VREG5 and REF are active.
Protection output is enabled Exited by VIN POR or by toggling EN, ENTRIPx
Either SMPS output is still high in During discharge mode, there is one path to discharge the
Discharge either standby mode or shutdown outputs capacitor residual charge. That is output capacitor
mode discharge to GND through an internal switch.
ENTRIPx < startup threshold,
Standby VREG3, VREG5 and REF are active.
EN = high.
Shutdown EN = low All circuitry off.
Thermal
TJ > 150°C All circuitry off. Exit by VIN POR or by toggling EN, ENTRIPx
Shutdown

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 RT8205L/M
Table 3. Power Up Sequencing
EN
ENTRIP1 ENTRIP2 REF VREG5 VREG3 SMPS1 SMPS2
(V)
Low X X Off Off Off Off Off
“>1V”
X X On On On Off Off
=> High
“>1V”
Off Off On On On Off Off
=> High
“>1V”
Off On On On On Off On
=> High
On
(after On
“>1V”
ENTRIP2 is On On On On (after SMPS2 On
=> High
On without is on)
60μs)
“>1V”
On Off On On On On Off
=> High
On
On
“>1V” (after ENTRIP1
On On On On On (after SMPS1
=> High is On without
is on)
60μs)
“>1V”
On On On On On On On
=> High

Output Voltage Setting (FBx) Output Inductor Selection

Connect a resistor voltage divider at the FBx pin between The switching frequency (on-time) and operating point (%
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VOUTx and GND to adjust the respective output voltage ripple or LIR) determine the inductor value as shown in
between 2V and 5.5V (Figure 6). Refering to Figure 5 as the following equation :
an example, choose R2 to be approximately 10kΩ, and tON × (VIN − VOUTx )
solve for R1 using the equation : L=
LIR × ILOAD(MAX)
⎛ ⎛ R1 ⎞ ⎞
VOUTx = VFBX × ⎜ 1+ ⎜ ⎟⎟ where LIR is the ratio of the peak to peak ripple current to
⎝ ⎝ R2 ⎠ ⎠
the average inductor current.
where VFBX is 2V. Find a low loss inductor having the lowest possible DC
VIN resistance that fits in the allotted dimensions. Ferrite cores
are often the best choice, although powdered iron is
VOUTx
UGATEx inexpensive and can work well at 200kHz. The core must
PHASEx be large enough not to saturate at the peak inductor current
LGATEx (IPEAK) :
R1
VOUTx IPEAK = ILOAD(MAX) + ⎡⎣(LIR / 2) × ILOAD(MAX) ⎤⎦
FBx

R2 The calculation above shall serve as a general reference.

To further improve the transient response, the output
inductance can be reduced even further. This needs to be
Figure 6. Setting VOUTx with resistor divider considered along with the selection of the output capacitor.

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RT8205L/M
Output Capacitor Selection The maximum power dissipation depends on the operating
The capacitor value and ESR determine the amount of ambient temperature for fixed T J (MAX) and thermal
output voltage ripple and load transient response. Thus, resistance, θJA. For the RT8205L/M package, the derating
the capacitor value must be greater than the largest value curve in Figure 7 allows the designer to see the effect of
calculated from below equations : rising ambient temperature on the maximum power
V dissipation.
(ΔILOAD )2 × L × (K OUTx + t OFF(MIN) )
VIN 2.0
VSAG =
⎡ ⎛ V − VOUTx ⎞ ⎤ Four-Layer PCB

Maximum Power Dissipation (W)1

2 × COUT × VOUTx × ⎢K ⎜ IN ⎟ − t OFF(MIN) ⎥
⎣ ⎝ VIN ⎠ ⎦ 1.6
2
(ΔILOAD ) × L
VSOAR =
2 × COUT × VOUTx 1.2

⎛ 1 ⎞ 0.8
VP−P = LIR × ILOAD(MAX) × ⎜ ESR + ⎟
⎝ 8 × COUT × f ⎠
0.4
where VSAG and VSOAR are the allowable amount of
undershoot voltage and overshoot voltage in the load
0.0
transient, Vp-p is the output ripple voltage, tOFF(MIN) is the 0 25 50 75 100 125
minimum off-time, and K is a factor listed in from Table 1. Ambient Temperature (°C)

Thermal Considerations Figure 7. Derating Curve for the RT8205L/M Package

For continuous operation, do not exceed absolute
Layout Considerations
maximum junction temperature. The maximum power
Layout is very important in high frequency switching
dissipation depends on the thermal resistance of the IC
converter designs, the PCB could radiate excessive noise
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package, PCB layout, rate of surrounding airflow, and

and contribute to the converter instability with improper
difference between junction and ambient temperature. The
layout. Certain points must be considered before starting
maximum power dissipation can be calculated by the
a layout using the RT8205L/M.
following formula :
` Place the filter capacitor close to the IC, within 12 mm
PD(MAX) = (TJ(MAX) − TA) / θJA
(0.5 inch) if possible.
where TJ(MAX) is the maximum junction temperature, TA is
` Keep current limit setting network as close as possible
the ambient temperature, and θJA is the junction to ambient
to the IC. Routing of the network should avoid coupling
thermal resistance.
to high voltage switching node.
For recommended operating condition specifications of
` Connections from the drivers to the respective gate of
the RT8205L/M, the maximum junction temperature is
the high side or the low side MOSFET should be as
125°C and TA is the ambient temperature. The junction to
short as possible to reduce stray inductance. Use 0.65
ambient thermal resistance, θJA, is layout dependent. For
mm (25 mils) or wider trace.
WQFN-24L 4x4 packages, the thermal resistance, θJA, is
52°C/W on a standard JEDEC 51-7 four-layer thermal test ` All sensitive analog traces and components such as
board. The maximum power dissipation at TA = 25°C can VOUTx, FBX, GND, ENTRIPx, PGOOD, and TONSEL
be calculated by the following formula : should be placed away from high voltage switching
nodes such as PHASEx, LGATEx, UGATEx, or BOOTx
PD(MAX) = (125°C − 25°C) / (52°C/W) = 1.923W for
nodes to avoid coupling. Use internal layer(s) as ground
WQFN-24L 4x4 package
plane(s) and shield the feedback trace from power traces
and components.

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 RT8205L/M
` Place the ground terminal of VIN capacitor(s), VOUTx
capacitor(s), and source of low side MOSFETs as close
as possible. The PCB trace defined as PHASEx node,
which connects to source of high side MOSFET, drain
of low side MOSFET and high voltage side of the
inductor, should be as short and wide as possible.

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RT8205L/M
Outline Dimension

D2 SEE DETAIL A
D

L
1

E E2

1 1

2 2

e b
DETAIL A
A
A3 Pin #1 ID and Tie Bar Mark Options
A1
Note : The configuration of the Pin #1 identifier is optional,
but must be located within the zone indicated.

Dimensions In Millimeters Dimensions In Inches

Symbol
Min Max Min Max
A 0.700 0.800 0.028 0.031
A1 0.000 0.050 0.000 0.002
A3 0.175 0.250 0.007 0.010
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b 0.180 0.300 0.007 0.012

D 3.950 4.050 0.156 0.159
D2 2.300 2.750 0.091 0.108
E 3.950 4.050 0.156 0.159
E2 2.300 2.750 0.091 0.108
e 0.500 0.020
L 0.350 0.450 0.014 0.018

W-Type 24L QFN 4x4 Package

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Headquarter Taipei Office (Marketing)
5F, No. 20, Taiyuen Street, Chupei City 5F, No. 95, Minchiuan Road, Hsintien City
Hsinchu, Taiwan, R.O.C. Taipei County, Taiwan, R.O.C.
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Email: marketing@richtek.com

Information that is provided by Richtek Technology Corporation is believed to be accurate and reliable. Richtek reserves the right to make any change in circuit
design, specification or other related things if necessary without notice at any time. No third party intellectual property infringement of the applications should be
guaranteed by users when integrating Richtek products into any application. No legal responsibility for any said applications is assumed by Richtek.

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