LTC4446

High Voltage High Side/

Low Side N-Channel
MOSFET Driver
FEATURES DESCRIPTION
n Bootstrap Supply Voltage Up to 114V The LTC®4446 is a high frequency high voltage gate driver
n Wide VCC Voltage: 7.2V to 13.5V that drives two N-channel MOSFETs in a DC/DC converter
n 2.5A Peak Top Gate Pull-Up Current with supply voltages up to 100V. The powerful driver ca-
n 3A Peak Bottom Gate Pull-Up Current pability reduces switching losses in MOSFETs with high
n 1.2Ω Top Gate Driver Pull-Down gate capacitance. The LTC4446’s pull-up for the top gate
n 0.55Ω Bottom Gate Driver Pull-Down driver has a peak output current of 2.5A and its pull-down
n 5ns Top Gate Fall Time Driving 1nF Load has an output impedance of 1.2Ω. The pull-up for the bot-
n 8ns Top Gate Rise Time Driving 1nF Load tom gate driver has a peak output current of 3A and the
n 3ns Bottom Gate Fall Time Driving 1nF Load pull-down has an output impedance of 0.55Ω.
n 6ns Bottom Gate Rise Time Driving 1nF Load
n
The LTC4446 is configured for two supply-independent
Drives Both High and Low Side N-Channel MOSFETs
n
inputs. The high side input logic signal is internally
Undervoltage Lockout
n
level-shifted to the bootstrapped supply, which may
Thermally Enhanced 8-Pin MSOP Package
function at up to 114V above ground.
The LTC4446 contains undervoltage lockout circuits that
APPLICATIONS disable the external MOSFETs when activated.
n Distributed Power Architectures The LTC4446 is available in the thermally enhanced 8-lead
n Automotive Power Supplies MSOP package.
n High Density Power Modules
n Telecommunication Systems The LTC4446 does not have adaptive shoot-through pro-
tection. For similar drivers with adaptive shoot-through
L, LT, LTC and LTM are registered trademarks of Linear Technology Corporation.
All other trademarks are the property of their respective owners. protection, please refer to the chart below.
Protected by U.S. Patents including 6677210.
PARAMETER LTC4446 LTC4444 LTC4444-5
Shoot-Through Protection No Yes Yes
Absolute Max TS 100V 100V 100V
MOSFET Gate Drive 7.2V to 13.5V 7.2V to 13.5V 4.5V to 13.5V
VCC UV+ 6.6V 6.6V 4V
VCC UV– 6.15V 6.15V 3.55V

TYPICAL APPLICATION
Two Switch Forward Converter LTC4446 Driving a 1000pF Capacitive Load
VIN BINP
VCC 36V TO 72V
7.2V TO 13.5V 5V/DIV
(100V ABS MAX)
BG
BOOST 10V/DIV
VCC TG
LTC4446 TINP
PWM1
TINP TS 5V/DIV
(FROM CONTROLLER IC) • • TO
PWM2 SECONDARY TG-TS
BINP BG
(FROM CONTROLLER IC) CIRCUIT 10V/DIV
GND
4446 TA01b
20ns/DIV

4446 TA01a
4446f

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LTC4446
ABSOLUTE MAXIMUM RATINGS PIN CONFIGURATION
(Note 1)
Supply Voltage TOP VIEW

VCC......................................................... –0.3V to 14V TINP 1 8 TS

BINP 2 7 TG
BOOST – TS ........................................... –0.3V to 14V VCC 3
9
6 BOOST
BG 4 5 NC
TINP Voltage ................................................. –2V to 14V
MS8E PACKAGE
BINP Voltage ................................................. –2V to 14V 8-LEAD PLASTIC MSOP
BOOST Voltage ........................................ –0.3V to 114V TJMAX = 125°C, θJA = 40°C/W, θJC = 10°C/W (NOTE 4)
TS Voltage................................................... –5V to 100V EXPOSED PAD (PIN 9) IS GND, MUST BE SOLDERED TO PCB

Operating Temperature Range (Note 2).... –40°C to 85°C

Junction Temperature (Note 3) ............................. 125°C
Storage Temperature Range................... –65°C to 150°C
Lead Temperature (Soldering, 10 sec) .................. 300°C

ORDER INFORMATION
LEAD FREE FINISH TAPE AND REEL PART MARKING* PACKAGE DESCRIPTION TEMPERATURE RANGE
LTC4446EMS8E#PBF LTC4446EMS8E#TRPBF LTDPZ 8-Lead Plastic MSOP –40°C to 85°C
LTC4446IMS8E#PBF LTC4446IMS8E#TRPBF LTDPZ 8-Lead Plastic MSOP –40°C to 85°C
Consult LTC Marketing for parts specified with wider operating temperature ranges. *The temperature grade is identified by a label on the shipping container.
Consult LTC Marketing for information on non-standard lead based finish parts.
For more information on lead free part marking, go to: http://www.linear.com/leadfree/
For more information on tape and reel specifications, go to: http://www.linear.com/tapeandreel/

ELECTRICAL CHARACTERISTICS The l denotes the specifications which apply over the full operating
temperature range, otherwise specifications are at TA = 25°C. VCC = VBOOST = 12V, VTS = GND = 0V, unless otherwise noted.
SYMBOL PARAMETER CONDITIONS MIN TYP MAX UNITS
Gate Driver Supply, VCC
VCC Operating Voltage 7.2 13.5 V
IVCC DC Supply Current TINP = BINP = 0V 350 550 μA
UVLO Undervoltage Lockout Threshold VCC Rising l 6.00 6.60 7.20 V
VCC Falling l 5.60 6.15 6.70 V
Hysteresis 450 mV
Bootstrapped Supply (BOOST – TS)
IBOOST DC Supply Current TINP = BINP = 0V 0.1 2 μA
Input Signal (TINP, BINP)
VIH(BG) BG Turn-On Input Threshold BINP Ramping High l 2.25 2.75 3.25 V
VIL(BG) BG Turn-Off Input Threshold BINP Ramping Low l 1.85 2.3 2.75 V
VIH(TG) TG Turn-On Input Threshold TINP Ramping High l 2.25 2.75 3.25 V
VIL(TG) TG Turn-Off Input Threshold TINP Ramping Low l 1.85 2.3 2.75 V
ITINP(BINP) Input Pin Bias Current ±0.01 ±2 μA
High Side Gate Driver Output (TG)
VOH(TG) TG High Output Voltage ITG = –10mA, VOH(TG) = VBOOST – VTG 0.7 V
VOL(TG) TG Low Output Voltage ITG = 100mA, VOL(TG) = VTG –VTS l 120 220 mV
IPU(TG) TG Peak Pull-Up Current l 1.7 2.5 A
RDS(TG) TG Pull-Down Resistance l 1.2 2.2 Ω
4446f

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 LTC4446
ELECTRICAL CHARACTERISTICS The l denotes the specifications which apply over the full operating
temperature range, otherwise specifications are at TA = 25°C. VCC = VBOOST = 12V, VTS = GND = 0V, unless otherwise noted.
SYMBOL PARAMETER CONDITIONS MIN TYP MAX UNITS
Low Side Gate Driver Output (BG)
VOH(BG) BG High Output Voltage IBG = –10mA, VOH(BG) = VCC – VBG 0.7 V
VOL(BG) BG Low Output Voltage IBG = 100mA l 55 110 mV
IPU(BG) BG Peak Pull-Up Current l 2 3 A
RDS(BG) BG Pull-Down Resistance l 0.55 1.1 Ω
Switching Time (BINP (TINP) is Tied to Ground While TINP (BINP) is Switching. Refer to Timing Diagram)
tPLH(TG) TG Low-High (Turn-On) Propagation Delay l 25 45 ns
tPHL(TG) TG High-Low (Turn-Off) Propagation Delay l 22 40 ns
tPLH(BG) BG Low-High (Turn-On) Propagation Delay l 19 35 ns
tPHL(BG) BG High-Low (Turn-Off) Propagation Delay l 14 30 ns
tDM(BGTG) Delay Matching BG Turn-Off and TG Turn-On l –15 10 35 ns
tDM(TGBG) Delay Matching TG Turn-Off and BG Turn-On l –25 –3 25 ns
tr(TG) TG Output Rise Time 10% – 90%, CL = 1nF 8 ns
10% – 90%, CL = 10nF 80 ns
tf(TG) TG Output Fall Time 10% – 90%, CL = 1nF 5 ns
10% – 90%, CL = 10nF 50 ns
tr(BG) BG Output Rise Time 10% – 90%, CL = 1nF 6 ns
10% – 90%, CL = 10nF 60 ns
tf(BG) BG Output Fall Time 10% – 90%, CL = 1nF 3 ns
10% – 90%, CL = 10nF 30 ns

Note 1: Stresses beyond those listed under Absolute Maximum Ratings with statistical process controls. The LTC4446I is guaranteed over the full
may cause permanent damage to the device. Exposure to any Absolute –40°C to 85°C operating temperature range.
Maximum Rating condition for extended periods may affect device Note 3: TJ is calculated from the ambient temperature TA and power
reliability and lifetime. dissipation PD according to the following formula:
Note 2: The LTC4446E is guaranteed to meet specifications from TJ = TA + (PD • θJA°C/W)
0°C to 85°C. Specifications over the –40°C to 85°C operating Note 4: Failure to solder the exposed back side of the MS8E package to the
temperature range are assured by design, characterization and correlation PC board will result in a thermal resistance much higher than 40°C/W.

TYPICAL PERFORMANCE CHARACTERISTICS

VCC Supply Quiescent Current BOOST-TS Supply Quiescent VCC Supply Current vs
vs Voltage Current vs Voltage Temperature
450 400 380
TA = 25°C TA = 25°C VCC = BOOST = 12V
VCC = 12V TINP = 12V, BINP = 0V TS = GND
400 BOOST = 12V TINP = BINP = 0V 350 370
TS = GND TS = GND
VCC SUPPLY CURRENT (μA)

350
QUIESCENT CURRENT (μA)

QUIESCENT CURRENT (μA)

300 360
300 TINP = BINP = 0V
250 TINP = 0V, BINP = 12V 350
TINP(BINP) = 12V
250
200 340
200
150 330
150 TINP(BINP) = 12V
100 320
100

50 50 310
TINP = BINP = 0V
0 0 300
0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 –40 –25 –10 5 20 35 50 65 80 95 110 125
VCC SUPPLY VOLTAGE (V) BOOST SUPPLY VOLTAGE (V) TEMPERATURE (°C)
4446 G01 4446 G02 4446 G03

4446f

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LTC4446
TYPICAL PERFORMANCE CHARACTERISTICS

Boost Supply Current Output Low Voltage (VOL) Output High Voltage (VOH) vs
vs Temperature vs Supply Voltage Supply Voltage
400 160 15
VCC = BOOST = 12V TINP = 12V TA = 25°C
TS = GND BINP = 0V 14 BOOST = VCC
350 140
TS = GND

TG OR BG OUTPUT VOLTAGE (V)

VOL(TG)
BOOST SUPPLY CURRENT (μA)

13
300 120

OUTPUT VOLTAGE (mV)

12
TINP = 0V 100 –1mA
250 11
BINP = 12V –10mA
200 80 10
VOL(BG) –100mA
9
150 60
8
100 40 TA = 25°C
7
ITG(BG) = 100mA
50 20 BOOST = VCC 6
TINP = BINP = 0V TS = GND
0 0 5
–40 –25 –10 5 20 35 50 65 80 95 110 125 7 8 9 10 11 12 13 14 7 8 9 10 11 12 13 14
TEMPERATURE (°C) SUPPLY VOLTAGE (V) SUPPLY VOLTAGE (V)
4446 G04 4446 G05 4446 G06

Input Thresholds (TINP, BINP) vs Input Thresholds (TINP, BINP) vs Input Thresholds (TINP, BINP)
Supply Voltage Temperature Hysteresis vs Voltage

TG OR BG INPUT THRESHOLD HYSTERESIS (mV)

3.1 3.0 500
TA = 25°C VCC = BOOST = 12V TA = 25°C
3.0 BOOST = VCC 2.9 TS = GND VCC = BOOST
TG OR BG INPUT THRESHOLD (V)
TG OR BG INPUT THRESHOLD (V)

TS = GND VIH(TG,BG) TS = GND

2.9 2.8 475
2.8 VIH(TG,BG) 2.7
2.7 2.6 450
2.6 2.5
2.5 2.4 425
VIL(TG,BG)
2.4 2.3
VIL(TG,BG)
2.3 2.2 400
2.2 2.1
2.1 2.0 375
7 8 9 10 11 12 13 14 –40 –25 –10 5 20 35 50 65 80 95 110 125 7 8 9 10 11 12 13 14
SUPPLY VOLTAGE (V) TEMPERATURE (°C) SUPPLY VOLTAGE (V)
4446 G07 4446 G08 4446 G09

Input Thresholds (TINP, BINP) VCC Undervoltage Lockout Rise and Fall Time vs
Hysteresis vs Temperature Thresholds vs Temperature VCC Supply Voltage
TG OR BG INPUT THRESHOLD HYSTERESIS (mV)

500 6.7 32
VCC = BOOST = 12V BOOST = VCC TA = 25°C
30
TS = GND TS = GND BOOST = VCC
6.6 28 TS = GND
475 tr(TG)
RISING THRESHOLD 26 CL = 3.3nF
VCC SUPLLY VOLTAGE (V)

6.5
RISE/FALL TIME (ns)

24
450 22
6.4 20 tr(BG)
18
425 6.3
16
14 tf(TG)
6.2 FALLING THRESHOLD
12
400
6.1 10
tf(BG)
8
375 6.0 6
–40 –25 –10 5 20 35 50 65 80 95 110 125 –40 –25 –10 5 20 35 50 65 80 95 110 125 7 8 9 10 11 12 13 14
TEMPERATURE (°C) TEMPERATURE (°C) SUPPLY VOLTAGE (V)
4446 G10 4446 G11 4446 G12

4446f

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 LTC4446
TYPICAL PERFORMANCE CHARACTERISTICS
Rise and Fall Time vs Peak Driver (TG, BG) Pull-Up Output Driver Pull-Down
Load Capacitance Current vs Temperature Resistance vs Temperature
2.0

OUTPUT DRIVER PULL-DOWN RESISTACNE (Ω)

80 3.4
TA = 25°C VCC = BOOST = 12V
VCC = BOOST = 12V TS = GND 1.8
70 3.2 BOOST-TS = 12V
TS = GND 1.6
60 BOOST-TS = 7V

PULL-UP CURRENT (A)

3.0 IPU(BG)
RISE/FALL TIME (ns)

tr(TG) 1.4
RDS(TG)
50 1.2 BOOST-TS = 14V
tr(BG) 2.8
40 1.0
VCC = 12V
2.6 0.8
30 IPU(TG) VCC = 7V
tf(TG) 0.6
2.4
20 VCC = 14V
0.4
tf(BG) 2.2 RDS(BG)
10 0.2

0 2.0 0
1 2 3 4 5 6 7 8 9 10 –40 –25 –10 5 20 35 50 65 80 95 110 125 –40 –25 –10 5 20 35 50 65 80 95 110 125
LOAD CAPACITANCE (nF) TEMPERATURE (°C) TEMPERATURE (°C)
4445 G13 4446 G14 4446 G15

Propagation Delay vs
VCC Supply Voltage Propagation Delay vs Temperature
30 37
TA = 25°C VCC = BOOST = 12V
28 BOOST = VCC TS = GND
tPLH(TG) TS = GND 32
26 tPLH(TG)
PROPAGATION DELAY (ns)

PROPAGATION DELAY (ns)

24 27 tPHL(TG)
tPHL(TG)
22
22
20 tPLH(BG) tPLH(BG)
18 17
tPHL(BG)
16 12
tPHL(BG)
14
7
12
10 2
7 8 9 10 11 12 13 14 –40 –25 –10 5 20 35 50 65 80 95 110 125
SUPPLY VOLTAGE (V) TEMPERATURE (°C)
4444 G16 4446 G17

Switching Supply Current vs Switching Supply Current vs

Input Frequency Load Capacitance
4.0
TA = 25°C
IBOOST
VCC = BOOST = 12V
3.5 IVCC (TG SWITCHING
TS = GND
IBOOST (BG SWITCHING AT 500kHz)
3.0 (TG SWITCHING) 100 AT 1MHz)
SUPPLY CURRENT (mA)

SUPPLY CURRENT (mA)

2.5 IVCC
(BG SWITCHING) IBOOST
(TG SWITCHING
2.0 10 IVCC AT 1MHz)
(BG SWITCHING
1.5 AT 500kHz) IVCC
IVCC (TG SWITCHING
1.0 IVCC 1 (TG SWITCHING AT 500kHz) AT 1MHz)
(TG SWITCHING)
0.5
IBOOST (BG SWITCHING AT 1MHz OR 5OOkHz)
IBOOST (BG SWITCHING)
0 0.1
0 200 400 600 800 1000 1 2 3 4 5 6 7 8 9 10
SWITCHING FREQUENCY (kHz) LOAD CAPACITANCE (nF)
4446 G18 4446 G19

4446f

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LTC4446
PIN FUNCTIONS
TINP (Pin 1): High Side Input Signal. Input referenced BOOST (Pin 6): High Side Bootstrapped Supply. An ex-
to GND. This input controls the high side driver output ternal capacitor should be tied between this pin and TS
(TG). (Pin 8). Normally, a bootstrap diode is connected between
VCC (Pin 3) and this pin. Voltage swing at this pin is from
BINP (Pin 2): Low Side Input Signal. This input controls
VCC – VD to VIN + VCC – VD, where VD is the forward volt-
the low side driver output (BG).
age drop of the bootstrap diode.
VCC (Pin 3): Supply. This pin powers input buffers, logic
and the low side gate driver output directly and the high TG (Pin 7): High Side Gate Driver Output (Top Gate). This
side gate driver output through an external diode con- pin swings between TS and BOOST.
nected between this pin and BOOST (Pin 6). A low ESR TS (Pin 8): High Side MOSFET Source Connection (Top
ceramic bypass capacitor should be tied between this pin Source).
and GND (Pin 9).
Exposed Pad (Pin 9): Ground. Must be soldered to PCB
BG (Pin 4): Low Side Gate Driver Output (Bottom Gate). ground for optimal thermal performance.
This pin swings between VCC and GND.
NC (Pin 5): No Connect. No connection required.

BLOCK DIAGRAM

6
BOOST VIN
VCC
3 VCC UVLO UP TO 100V
7.2V TO
13.5V GND
9 HIGH SIDE TG
7
LEVEL SHIFTER
LDO VINT TS
8

TINP VCC VCC

1

LOW SIDE BG
BINP 4
2 LEVEL SHIFTER

NC
5 4446 BD

TIMING DIAGRAM
INPUT RISE/FALL TIME < 10ns
90%
TINP (BINP)
10%

BINP (TINP)

BG (TG)

90% 90%
TG (BG)
10% 10%
tr tf 4444 TD

tPHL tPLH
4446f

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 LTC4446
OPERATION
Overview LTC4446 BOOST VIN
6 UP TO 100V
The LTC4446 receives ground-referenced, low voltage digi-
tal input signals to drive two N-channel power MOSFETs in Q1 CGD
TG HIGH SIDE
a synchronous buck power supply configuration. The gate 7 POWER
of the low side MOSFET is driven either to VCC or GND, M1 CGS
MOSFET
TS
depending on the state of the input. Similarly, the gate of 8 LOAD
the high side MOSFET is driven to either BOOST or TS by VCC INDUCTOR
a supply bootstrapped off of the switching node (TS). 3

Input Stage Q2 CGD

BG LOW SIDE
4 POWER
The LTC4446 employs CMOS compatible input thresholds CGS
MOSFET
M2 GND
that allow a low voltage digital signal to drive standard 9
power MOSFETs. The LTC4446 contains an internal 4446 F01

voltage regulator that biases both input buffers for high

side and low side inputs, allowing the input thresholds Figure 1. Capacitance Seen by BG and TG During Switching
(VIH = 2.75V, VIL = 2.3V) to be independent of variations in
VCC. The 450mV hysteresis between VIH and VIL eliminates Rise/Fall Time
false triggering due to noise during switching transitions.
However, care should be taken to keep both input pins The LTC4446’s rise and fall times are determined by the
(TINP and BINP) from any noise pickup, especially in high peak current capabilities of Q1 and M1. The predriver that
frequency, high voltage applications. The LTC4446 input drives Q1 and M1 uses a nonoverlapping transition scheme
buffers have high input impedance and draw negligible to minimize cross-conduction currents. M1 is fully turned
input current, simplifying the drive circuitry required for off before Q1 is turned on and vice versa.
the inputs. Since the power MOSFET generally accounts for the ma-
jority of the power loss in a converter, it is important to
Output Stage quickly turn it on or off, thereby minimizing the transition
A simplified version of the LTC4446’s output stage is shown time in its linear region. An additional benefit of a strong
in Figure 1. The pull-up devices on the BG and TG outputs pull-down on the driver outputs is the prevention of cross-
are NPN bipolar junction transistors (Q1 and Q2). The BG conduction current. For example, when BG turns the low
and TG outputs are pulled up to within an NPN VBE (~0.7V) side (synchronous) power MOSFET off and TG turns the
of their positive rails (VCC and BOOST, respectively). Both high side power MOSFET on, the voltage on the TS pin
BG and TG have N-channel MOSFET pull-down devices will rise to VIN very rapidly. This high frequency positive
(M1 and M2) which pull BG and TG down to their nega- voltage transient will couple through the CGD capacitance
tive rails, GND and TS. The large voltage swing of the BG of the low side power MOSFET to the BG pin. If there is
and TG output pins is important in driving external power an insufficient pull-down on the BG pin, the voltage on
MOSFETs, whose RDS(ON) is inversely proportional to the the BG pin can rise above the threshold voltage of the low
gate overdrive voltage (VGS − VTH). side power MOSFET, momentarily turning it back on. With

4446f

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LTC4446
OPERATION
both the high side and low side MOSFETs conducting, load with 6ns rise and 3ns fall times using a supply volt-
significant cross-conduction current will flow through the age VCC of 12V.
MOSFETs from VIN to ground and will cause substantial
power loss. A similar effect occurs on TG due to the CGS Undervoltage Lockout (UVLO)
and CGD capacitances of the high side MOSFET. The LTC4446 contains an undervoltage lockout detector
The powerful output driver of the LTC4446 reduces the that monitors VCC supply. When VCC falls below 6.15V,
switching losses of the power MOSFET, which increase the output pins BG and TG are pulled down to GND and
with transition time. The LTC4446’s high side driver is TS, respectively. This turns off both external MOSFETs.
capable of driving a 1nF load with 8ns rise and 5ns fall When VCC has adequate supply voltage, normal operation
times using a bootstrapped supply voltage VBOOST-TS of will resume.
12V while its low side driver is capable of driving a 1nF

APPLICATIONS INFORMATION
Power Dissipation The LTC4446 consumes very little quiescent current. The
DC power loss at VCC = 12V and VBOOST-TS = 12V is only
To ensure proper operation and long-term reliability, the
(350μA)(12V) = 4.2mW.
LTC4446 must not operate beyond its maximum tem-
perature rating. Package junction temperature can be At a particular switching frequency, the internal power loss
calculated by: increases due to both AC currents required to charge and
discharge internal node capacitances and cross-conduc-
TJ = TA + PD (θJA)
tion currents in the internal logic gates. The sum of the
where: quiescent current and internal switching current with no
TJ = Junction temperature load are shown in the Typical Performance Characteristics
plot of Switching Supply Current vs Input Frequency.
TA = Ambient temperature
The gate charge losses are primarily due to the large AC
PD = Power dissipation currents required to charge and discharge the capacitance
θJA = Junction-to-ambient thermal resistance of the external MOSFETs during switching. For identical
pure capacitive loads CLOAD on TG and BG at switching
Power dissipation consists of standby and switching frequency fIN, the load losses would be:
power losses:
PCLOAD = (CLOAD)(f)[(VBOOST-TS)2 + (VCC)2]
PD = PDC + PAC + PQG
In a typical synchronous buck configuration, VBOOST-TS
where: is equal to VCC – VD, where VD is the forward voltage
PDC = Quiescent power loss drop across the diode between VCC and BOOST. If this
drop is small relative to VCC, the load losses can be
PAC = Internal switching loss at input frequency, fIN
approximated as:
PQG = Loss due turning on and off the external MOSFET
PCLOAD = 2(CLOAD)(fIN)(VCC)2
with gate charge QG at frequency fIN

4446f

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 LTC4446
APPLICATIONS INFORMATION
Unlike a pure capacitive load, a power MOSFET’s gate B. Use a low inductance, low impedance ground plane
capacitance seen by the driver output varies with its VGS to reduce any ground drop and stray capacitance.
voltage level during switching. A MOSFET’s capacitive load Remember that the LTC4446 switches greater than
power dissipation can be calculated using its gate charge, 3A peak currents and any significant ground drop will
QG. The QG value corresponding to the MOSFET’s VGS degrade signal integrity.
value (VCC in this case) can be readily obtained from the C. Plan the power/ground routing carefully. Know where
manufacturer’s QG vs VGS curves. For identical MOSFETs the large load switching current is coming from and
on TG and BG: going to. Maintain separate ground return paths for
PQG = 2(VCC)(QG)(fIN) the input pin and the output power stage.
To avoid damage due to power dissipation, the LTC4446 D. Keep the copper trace between the driver output pin
includes a temperature monitor that will pull BG and TG and the load short and wide.
low if the junction temperature rises above 160°C. Normal E. Be sure to solder the Exposed Pad on the back side of
operation will resume when the junction temperature cools the LTC4446 package to the board. Correctly soldered
to less than 135°C. to a 2500mm2 doublesided 1oz copper board, the
LTC4446 has a thermal resistance of approximately
Bypassing and Grounding
40°C/W for the MS8E package. Failure to make good
The LTC4446 requires proper bypassing on the VCC thermal contact between the exposed back side and
and VBOOST-TS supplies due to its high speed switching the copper board will result in thermal resistances far
(nanoseconds) and large AC currents (Amperes). Careless greater than 40°C/W.
component placement and PCB trace routing may cause
excessive ringing.
To obtain the optimum performance from the LTC4446:
A. Mount the bypass capacitors as close as possible
between the VCC and GND pins and the BOOST and
TS pins. The leads should be shortened as much as
possible to reduce lead inductance.

4446f

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 LTC3722/LTC4446 420W 36V-72VIN to 12V/35A Isolated Full-Bridge Supply

10
L1 VIN 51Ω
1.3μH 2W
VIN T1 2k
1μF 1μF 12V 12V 5(105μH):1:1 1/2W
LTC4446

36V TO 72V 100V 100V D2 D3 VOUT

0.47μF 4 11
–VIN s4 0.47μF 100V D5 470pF
3 3 D4 200V
100V

•
10 47Ω
VCC VCC
1 6 1 6 51Ω 1W 0.82μF

•
A TINP BOOST TINP C BOOST 2
2W 100V
LTC4446 LTC4446 8 VH D6
2 7 Si7852DP 2 7 Si7852DP –VOUT
B BINP TG D BINP TG
s2 s2

•
7 L3
BG GND TS BG GND TS
0.85μH

•
VOUT
4 9 8 0.22μF 4 9 8 0.22μF 4 11

•
L2 VH VOUT

•
150nH 10
TYPICAL APPLICATION

C1, C2

•
2 +
180μF
0.47μF, 100V TDK C3216X7R2A474M 8 16V
1μF, 100V TDK C4532X7R2A105M s2
1μF

•
C1,C2: SANYO 16SP180M 7
Si7852DP Si7852DP 12V/35A
C3: AVX TPSE686M020R0150
s2 ×2
C4: MURATA DE2E3KH222MB3B Si7852DP Si7852DP
D4-D6: MURS120T3 s4 s4
D2, D3, D7, D8: BAS21 T2
D9: MMBZ5226B 5:5(105μH):1:1
VOUT
D10: MMBZ5240B L4 –VOUT
D11: BAT54 1k 12V 100Ω 1mH D7 Q1 Q2 VOUT –VOUT
D12: MMBZ231B ISNS
4.87k 4.87k
L1: SUMIDA CDEP105-1R3MC-50 0.02Ω 0.02Ω C3 6
+ 1/4W Q3 1/4W Q4
L2: PULSE PA0651 1.5W 1.5W 68μF D8
L3: PA1294.910 20V D9 3.3V

•
L4: COILCRAFT DO1608C-105 1 VOUT
2.21k 1.5k 2.21k 1.5k
Q1, Q2: ZETEX FMMT619
Q3, Q4: ZETEX FMMT718 6 5 2 3 11 12 14 15 16
T1, T2: PULSE PA0526 T3 100Ω 1k
CSE+ CSE– ME ME2 CSF+ CSF– MF MF2 VCC 39.2k
T3: PULSE PA0297 B C 1(1.5μH):0.5 MMBT3904
1 4 9 1
SYNC LTC3901EGN

•
•
PVCC
80.6k 68.1k 18.2k
0.1μF D10
22Ω 100Ω GND PGND GND2 PGND2 TIMER 10V
80.6k 8 5 1μF
8 4 10 13 7
220pF 1μF
VIN 12V 4.99k 22pF 22pF 4.99k 330pF

20k A B C D
1/4W ISNS 5VREF VOUT –VOUT
11 9 21 20 19 17 15 16 330Ω 470Ω
200k 1/4W
10 ADLY PDLY OUTA OUTB OUTC OUTD OUTF OUTE
150Ω SBUS 1
3 750Ω 10k
18 CS MOC207 2.7k 9.53k
182k VIN LTC3722EGN-1
12 6 22nF
UVLO 0.047μF
3
VREF DPRG NC SYNC CT SPRG RLEB FB GND PGND SS COMP V +

220pF 14 2 8 1 24 13 5 6 23 22 7 4 5 8 2 LT1431CS8 8
1
5VREF 20k MMBT3904 COLL REF
1μF 5.1k 6.19k 2.2nF
D11 C4 D12
8.25k GND-F GND-S 2.49k
30.1k 2.2nF 5.1V
0.47μF 220pF 180pF 33k 1M 330pF
250V 6 5
68nF
–VOUT
4446 TA02a

4446f
 LTC4446
PACKAGE DESCRIPTION
MS8E Package
8-Lead Plastic MSOP, Exposed Die Pad
(Reference LTC DWG # 05-08-1662 Rev D)

BOTTOM VIEW OF
EXPOSED PAD OPTION
2.06 ± 0.102
1 (.081 ± .004)
1.83 ± 0.102
2.794 ± 0.102 0.889 ± 0.127 (.072 ± .004)
(.110 ± .004) (.035 ± .005)

5.23
(.206) 2.083 ± 0.102 3.20 – 3.45
MIN (.082 ± .004) (.126 – .136)

8
3.00 ± 0.102
0.42 ± 0.038 0.65 (.118 ± .004) 0.52
(.0165 ± .0015) (.0256) (NOTE 3) 8 7 6 5 (.0205)
TYP BSC REF
RECOMMENDED SOLDER PAD LAYOUT

3.00 ± 0.102
4.90 ± 0.152
DETAIL “A” (.118 ± .004)
0.254 (.193 ± .006)
(NOTE 4)
(.010)
0° – 6° TYP
GAUGE PLANE
1 2 3 4
0.53 ± 0.152
(.021 ± .006) 1.10 0.86
(.043) (.034)
DETAIL “A” MAX REF
0.18
(.007)
SEATING
PLANE 0.22 – 0.38 0.1016 ± 0.0508
(.009 – .015) (.004 ± .002)
0.65
TYP MSOP (MS8E) 0307 REV D
(.0256)
NOTE:
BSC
1. DIMENSIONS IN MILLIMETER/(INCH)
2. DRAWING NOT TO SCALE
3. DIMENSION DOES NOT INCLUDE MOLD FLASH, PROTRUSIONS OR GATE BURRS.
MOLD FLASH, PROTRUSIONS OR GATE BURRS SHALL NOT EXCEED 0.152mm (.006") PER SIDE
4. DIMENSION DOES NOT INCLUDE INTERLEAD FLASH OR PROTRUSIONS.
INTERLEAD FLASH OR PROTRUSIONS SHALL NOT EXCEED 0.152mm (.006") PER SIDE
5. LEAD COPLANARITY (BOTTOM OF LEADS AFTER FORMING) SHALL BE 0.102mm (.004") MAX

4446f

11
Information furnished by Linear Technology Corporation is believed to be accurate and reliable.
However, no responsibility is assumed for its use. Linear Technology Corporation makes no representa-
tion that the interconnection of its circuits as described herein will not infringe on existing patent rights.
LTC4446
TYPICAL APPLICATION
LTC4446 Fast Turn-On/Turn-Off DC Switch

12V VIN
0V TO 100V

0.33μF
3 6
0.01μF
BZX84C12L 15k VCC BOOST
12V BAS21 100V 1 7
200Ω TINP TG
4.7k 2 LTC4446 8
BAS21 100k BINP TS

4.7nF BG GND BAS21

MMBT2369 9 3.3nF
LOAD

4446 TA03

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No RSENSE is a trademark of Linear Technology Corporation.

4446f

LT 0508 • PRINTED IN USA

12 Linear Technology Corporation

1630 McCarthy Blvd., Milpitas, CA 95035-7417
(408) 432-1900 ● FAX: (408) 434-0507 ● www.linear.com © LINEAR TECHNOLOGY CORPORATION 2008