UNISONIC TECHNOLOGIES CO.

, LTD
UC3862 CMOS IC

LOW COST POWER-SAVING

MODE PWM CONTROLLER
FOR FLYBACK CONVERTERS
4
5
6
 DESCRIPTION
3
2
The UTC UC3862 provides a CCM/valley switching mixed 1
mode operation for better efficiency performance. The operation
mode stays at CCM at heavy load, and switch to valley switching at SOT-26
light load.
The UTC UC3862 is a high performance current mode PWM
controller ideally suited for low standby power. Low VCC startup
current make the power reliable on startup design and a large
value resistor could be used in the startup circuit to minimize the
standby power. At no load condition, the IC operates in
power-saving mode for lower standby power, decreasing frequency
for Higher conversion efficiency at light load condition.
The UTC UC3862 contains protection with automatic recovery
including OLP (over load protection), OCP (cycle-by-cycle current
limiting), and UVLO (VCC over voltage clamp and under voltage
lockout). It also provides the protections including OTP (over
temperature protection), BNO(AC Brown Out protection) , LNO(AC
Over voltage protection), OVP (VCC or DC output over voltage
protection) with automatic recovery. To protect the power
MOSFET, Gate-drive output is fixed up to 16V max.
The internal slope compensation improves system stability at
high PWM duty cycle output. Leading-edge blanking on current
sense input removes the signal glitch, which offering minima
external component count in the design. Excellent EMI
performance is achieved with UTC proprietary frequency hopping
technique (ZL201020615247.1) together with soft driver control.
Audio noise is eliminated due to switch frequency more than 20kHz
during operation.
UTC UC3862 is packaged by using tiny SOT-26 package. It has
such applications as: battery charger, power adaptor, set-top box
power supplies, ink jet printers, open-frame SMPS.
 FEATURES
* Proprietary frequency hopping for Improved EMI performance
* Cycle-by-cycle current limiting
* CCM/Valley Switching Operation
* Fixed switch frequency 60~70kHz
* Dynamic peak current limiting for constant output power
* Built-in synchronized slope compensation
* Gate output voltage clamped at 16V
* Adjustable DC output OVP/UVP/OTP
* OLP/VCC OVP/OTP/BNO/LNO (automatic recovery)
* Internal Soft Start

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UC3862 CMOS IC

 ORDERING INFORMATION
Ordering Number
Package Packing
Lead Free Halogen Free
UC3862L-AG6-R UC3862G-AG6-R SOT-26 Tape Reel

 MARKING

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UC3862 CMOS IC

 PIN CONFIGURATION

 PIN DESCRIPTION
PIN NO. PIN NAME DESCRIPTION
1 GND Ground
Feedback input pin. The PWM duty cycle is determined by voltage level into this pin and
2 FB
SENSE pin input
Demagnetization detection signal. This pin can also provide adjustable output voltage
3 DEM
OVP and AC brown in/out protection
4 CS Current sense input pin. Connected to MOSFET current sensing resistor node
5 VCC Power supply
6 OUT The totem-pole output driver for driving the power MOSFET

 BLOCK DIAGRAM

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UC3862 CMOS IC

 ABSOLUTE MAXIMUM RATING

PARAMETER SYMBOL RATINGS UNIT
Supply Voltage VCC -0.3 ~ 36 V
Input Voltage to OUT Pin VOUT -0.3 ~ VCC+0.3 V
FB, CS, DEM -0.3 ~ 6 V
Power Dissipation @ TA=+25°C PD 400 mW
Junction Temperature TJ +150 °C
Operating Ambient Temperature TOPR -40 ~ +85 °C
Storage Temperature Range TSTG -65 ~ +150 °C
Note: Absolute maximum ratings are those values beyond which the device could be permanently damaged.
Absolute maximum ratings are stress ratings only and functional device operation is not implied.
 RECOMMENDED OPERATING CONDITIONS
PARAMETER SYMBOL RATINGS UNIT
Supply Voltage VCC 9 ~ 28 V
Start up Resistor 0.86 ~ 4.4 MΩ
VCC Capacitor 2.2 ~ 4.7 μF

 THERMAL CHARACTERISTICS
PARAMETER SYMBOL RATING UNIT
Junction to Ambient θJA 250 °C/W

 ELECTRICAL CHARACTERISTICS (VCC=15V, TA=25°C, unless otherwise specified)

PARAMETER SYMBOL TEST CONDITIONS MIN TYP MAX UNIT
Supply Voltage
VCC (ON) VCC_ON 14 16 18 V
VCC (OFF) VCC_MIN 6.6 7.6 8.6 V
Startup Current ISTR VCC<VCC(ON)-0.5V 1 5 μA
VFB=2.1V 0.68 mA
Operating Current IOP
VFB=Burst Level 0.5 mA
VCC OVP Threshold VCC_OVP VFB=2.1V 29 31 34 V
Oscillator & Switching Frequency
Normal mode Switching Frequency F_SW VFB=2.1V 60 65 70 KHz
Peak mode Switching Frequency F_SW_PK Only for UC3862, VFB=3.5V 130 KHz
Temperature Stability FDT Guaranteed by Design 10 %
Voltage Stability FDV 10 %
Green Mode Frequency F_SW_GR 20 KHz
Frequency Spreading Range ΔOSC VFB=2.1V +9 -9 %
Max. Duty Cycle DC_MAX VFB=2.1V, VCS=0V 58 64 70 %
Voltage Feedback
Open Loop Voltage VFB_OPEN 5.00 5.40 5.80 V
OLP Level VFB_OLP 4.4 4.65 4.9 V
OLP De-Bounce Time TD_OLP VFB>5V 45 mS
Burst-Mode Enter FB Voltage VFB_IN 0.85 V
Burst-Mode Quit FB Voltage VFB_OUT 0.95 V
FB Pin Short Current IFB_SHORT 60 μA

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UC3862 CMOS IC

 ELECTRICAL CHARACTERISTICS (Cont.)

PARAMETER SYMBOL TEST CONDITIONS MIN TYP MAX UNIT
Current Sensing
Current Limiting Threshold Voltage
VCS_L VFB=2.8V 0.40 0.45 0.50 V
With 50% Duty
Maximum Input Voltage VCS_LIMIT Guaranteed by Design 0.59 V
Lead Edge Blanking Time TLEB Guaranteed by Design 350 ns
SDSP(Secondary Diode Short
VSCP Guaranteed by Design 1.22 1.32 1.42 V
Protection) CS pin Level
CS OTP Level VCS_OTP Guaranteed by Design 0.44 V
IDEM=100μA
MIN. OCP Compensation Current IOCP_MIN 162.5 μA
Guaranteed by Design
IDEM=300μA
MAX.OCP Compensation Current ICCP_MAX 487.5 μA
Guaranteed by Design
Soft Start Time Guaranteed by Design 10 mS
Gate Drive Output
Output Low Level VOL VCC=15V, IOUT=-20mA 1 V
Output High Level VOH VCC=15V, IOUT=20mA 9 V
Rising Time tR 10% to 90% of VOUT, CL=1nF 200 nS
Falling Time tF 90% to 10% of VOUT, CL=1nF 60 nS
Out Clamping Vclamp VCC=20V 15 V
Demagnetization (DEM) Detection
DEM OVP Sampling Instant TDEM_OVP1 Guaranteed by Design 3 μS
DEM OVP Threshold Level VDEM_OVP 2.7 3.0 3.3 V
Output UVP Trigger Point VDEM_UVP Guaranteed by Design 0.8 V
DEM OVP De-Bounce Time TDEM_OVP2 Guaranteed by Design 7 Times
Demagnetization Detection Level VQR Guaranteed by Design 220 mV
Demagnetization Delay TQR Guaranteed by Design 200 nS
DEM_BNI IBNI Guaranteed by Design 100 110 120 μA
DEM_BNO IBNO 90 100 110 μA
BNO De-Bounce Time TBNO Guaranteed by Design 60 mS
Threshold Current of Line Voltage
ILNO Guaranteed by Design 320 345 370 μA
OVP
Thermal Shut Down
OTP Threshold OTP 150 °C

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UC3862 CMOS IC

 APPLICATION NOTE
The UTC UC3862 devices integrate many useful designs into one controller for low-power switch-mode power
supplies. The following descriptions highlight some of the features of the UTC UC3862 series.
Start-up Current
The start-up current is only 1μA. Low start-up current allows a start-up resistor with a high resistance and a
low-wattage to supply the start-up power for the controller. For AC/DC adaptor with universal input range design, a
2.5~3MΩ, 1/8W startup resistor could be used together with a VCC capacitor to provide a fast startup and low power
dissipation solution. The D1 IN4148 can improve surge capability to 6.6KV.

Operation Mode
The UTC UC3862 provides a CCM/valley switching mixed mode operation for better efficiency performance. The
operation mode stays at CCM at heavy load, once if the converter enters into DCM, the UTC UC3862 automatically
finds the local minimum VDS point and switching at this local valley. Peak load mode for heavy load condition.
Normally, the conduction loss is dominated at heavy load condition, and the switching loss turns to be larger than
conduction loss in light load, especially at 1/4 ~ 1/2 of full load. By this kind of mixed mode operation to have CCM in
heavy load and valley switching in light load can optimize the overall average efficiency during the entire operation
range.

FSW

130KHz

65KHz

CCM or valley Peaking load

Pulse
switching switching
skipping

23KHz
Valley switching
and extended
VFB

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UC3862 CMOS IC

 APPLICATION NOTE (Cont.)

As shown in Fig. 3, at deep light-load or no-load condition, the switching loss is the dominant factor. To improve
the light-load efficiency, burst mode operation will stop the switching cycle of the OUT pin when FB pin voltage is
below “VFB_IN” Level and restart the switching cycle of the OUT pin when FB pin voltage is above “VFB_OUT”.

VFB
VFB_OUT

VFB_IN
T
VOUT

No No No
switching switching switching

T
Fig. 3 Burst Mode Operation

Over Voltage Protection on VCC Pin ( VCC OVP )

The VCC OVP will shut down the switching of the power MOSFET whenever VCC >VOVP. The OVP event as
followed Fig.4.

Fig.4 OVP case Fig.5 OLP case

Over Load &Open Loop & Output Short Protection ( OLP or OSP )
OLP or OSP will shut down driver when VFB > VOLP for continual a blanking time. The OLP or OSP event as
followed Fig.5.
Over Temperature Protection ( OTP )
OTP will shut down driver when the NTC resistor temperature TJ>T (THR).
Brown in/out and Line input OVP & DEM OVP/UVP Protection
To prevent high current stress at too low AC voltage condition, the UTC UC3862 implements an AC brown in/out
protection through the DEM pin. The current sourcing out from the DEM pin when the OUT pin is enabled is
monitored to have the AC input voltage level information. When the current keeps above the DEM_BNI threshold
(IBNI) for more than BNI De-bounce time 7 cycles, the AC brown in condition is issued and the OUT is enabled. Once
if the current keeps under the DEM_BNO threshold (IBNO) for more than BNO De-bounce time, the AC brown out
condition is issued and the OUT is disabled.
The equation is used to calculate the brown in/out level:
R DEM _ U NPRI R DEM _ U NPRI
VAC _ BNI = IBNI × × , VAC _ BNO = IBNO × ×
2 N AUX 2 N AUX

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UC3862 CMOS IC
 APPLICATION NOTE (Cont.)
To prevent line AC input voltage too high, the UTC UC3862 implements an AC input LNO protection through the
DEM pin. The current sourcing out from the DEM pin when the OUT pin is enabled is monitored to have the AC input
voltage level information. When the current keeps above the DEM_LNO threshold (ILNO) for more than LNO
De-bounce time 7 cycles, AC input LNO protection is enabled and the out is off.
The equation is used to calculate the LNO level:
R DEM _ U NPRI
VAC _ LNO = ILNO × ×
2 N AUX
An over voltage protection for Vo is fulfilled by sampling the voltage on the DEM waveform after OUT is turn-off.
After a short delay after OUT off, the sampled voltage is compared to the internal over voltage reference is
determined whether if an OVP event is occurred. The internal over voltage reference is biased at VDEM_OVP, uses can
define the resistor divider ratio by the equation below based on the desired OVP level:
RDEM _ U + RDEM _ D NSEC
VO _ OVP = VDEM _ OVP × ×
RDEM _ D NAUX

An under voltage protection for Vo is fulfilled by sampling the voltage on the DEM waveform after OUT is turn-off.
After a short delay after OUT off, the sampled voltage is compared to the internal under voltage reference is
determined whether if an UVP event is occurred. The internal under voltage reference is biased at VDEM_UVP, uses can
define the resistor divider ratio by the equation below based on the desired UVP level:
RDEM _ U + RDEM _ D NSEC
VO _ UVP = VDEM _ UVP × ×
RDEM _ D NAUX

VCC
NAUX
+
RDEM_UP
UC3862
DCOVP
DCUVP
DEM
BNO
RDEM_DOWN LNO
Valley Detection

Fig. 6 DEM-Pin Divider

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UC3862 CMOS IC

 APPLICATION NOTE (Cont.)

Cycle by Cycle Over-Current Protection ( OCP )

In a Flyback topology converter, the main MOSFET switch of the Flyback converter turns on and off rapidly. The
energy is stored in the inductor when the MOSFET turns on. The inductor current flowing through the sensing
resistor (RCS) is shown in Fig.7. The current limit is determined by the equation below:
V
IPEAK = CS
RCS
In order to prevent the CS pin from false triggering, an internal leading edge blanking time (350nS Typ.) is added
and an external low pass RC filter is also recommended to filter the turn-on spike of CS node.
ICS_Comp (uA)

Fig. 7 Current Sensing

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UC3862 CMOS IC

 TYPICAL APPLICATION CIRCUIT

UTC assumes no responsibility for equipment failures that result from using products at values that
exceed, even momentarily, rated values (such as maximum ratings, operating condition ranges, or other
parameters) listed in products specifications of any and all UTC products described or contained herein.
UTC products are not designed for use in life support appliances, devices or systems where malfunction
of these products can be reasonably expected to result in personal injury. Reproduction in whole or in
part is prohibited without the prior written consent of the copyright owner. UTC reserves the right to
make changes to information published in this document, including without limitation specifications and
product descriptions, at any time and without notice. This document supersedes and replaces all
information supplied prior to the publication hereof.

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