Datasheet

UNISONIC TECHNOLOGIES CO., LTD
US3651
Preliminary
CMOS IC
HIGH PRECISION CC/CV
PRIMARY-SIDE PWM POWER
SWITCH

DIP-8
DESCRIPTION
The UTC US3651 is a primary control switch mode charger and
adapter applications. The controlled variable is transferred by an
auxiliary winding from the secondary to the primary side. The
device integrates PWM controller to enhance the performance of
discontinuous conduction mode (DCM) flyback converters.
The UTC US3651 operates in primary-side sensing and
regulation. Opto-coupler and TL431 could be eliminated. It also
provides off-time modulation to linearly decrease PWM frequency
under light-load conditions so that low standby power can be
achieved.
The UTC US3651 achieves high precision CV/CC regulation
and high power efficiency. It offers comprehensive protection
coverage with auto-recovery features including Cycle-by-cycle
current limiting, VDD over voltage protection, VDD clamp, OTP,
leading edge blanking, VDD under voltage lockout, etc.

FEATURES
* Built-in 600V Power MOSFET
* ±5% constant voltage regulation at universal AC input
* High precision constant current regulation at universal AC input
* Primary side control without TL431 and opto-coupler
* Programmable CV and CC regulation
* Programmable cable compensation in CV mode
* Flyback topology in DCM operation
* Frequency hopping to reduce system EMI
* Built-in leading edge blanking

SOP-8
* Built-in primary winding inductance
compensation
* Power on soft start
* Gate Output Maximum Voltage Clamped at
15V
* Cycle-by-cycle current limiting
* Over voltage protection
* VDD under-voltage lockout
ORDERING INFORMATION
Ordering Number
Lead Free
Halogen Free
US3651L-D08-T
US3651G-D08-T
US3651G-S08-R
Package
Packing
DIP-8
SOP-8
Tube
Tape Reel
US3651L-D08-T
(1)Packing Type
(1) T: Tube, R: Tape Reel
(2)Package Type
(2) D08: DIP-8, S08: SOP-8
(3)Green Package
(3) L: Lead Free, G: Halogen Free and Lead Free
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Copyright © 2015 Unisonic Technologies Co., Ltd
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US3651

Preliminary
CMOS IC
MARKING
DIP-8


SOP-8
PIN CONFIGURATION
VDD
1
8
GND
COMP
2
7
GND
INV
3
6
DRAIN
CS
4
5
DRAIN
PIN DESCRIPTION
PIN NO.
1
2
3
4
5/6
7/8
PIN NAME
VDD
COMP
INV
CS
DRAIN
GND
DESCRIPTION
Power Supply
Loop Compensation
The voltage feedback from the auxiliary winding
Current sense input
Power MOSFET Drain Pin
Ground
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US3651

Preliminary
CMOS IC
BLOCK DIAGRAM
VDD
1
5/6 DRAIN
Por
Regulator
& VREF
Logic core
Power
MOSFET
OVP
Softstart
26V
Tdemag
detector
CC
controller
INV 3
LEB
CV
controller
2V
4 CS
0.76V
Cable
compensation
2
7/8
COMP
GND
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Drive
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US3651

Preliminary
CMOS IC
ABSOLUTE MAXIMUM RATING
PARAMETER
SYMBOL
RATINGS
UNIT
Drain Voltage (Off State)
BVDSS
-0.3~Bvdss
V
VDD Zener Clamp Continuous Current
IDD
10
mA
COMP Voltage
VCOMP
-0.3~7
V
CS Input Voltage
VCS
-0.3~7
V
INV Input Voltage
VINV
-0.3~7
V
Operating Junction Temperature
TJ
-20~150
°C
Storage Temperature
TSTG
-55~150
°C
Notes: 1. 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.
2. Drain Pin Connected 100mm2 PCB copper clad.

THERMAL CHARACTERISTICS
PARAMETER
Junction to Ambient

SYMBOL
DIP-8
SOP-8
θJA
RATINGS
75
90
UNIT
°C/W
°C/W
OUTPUT POWER TABLE
PARAMETER
RATINGS
UNIT
230VAC±15%
6
W
Adapter (Note)
85-264VAC
5
W
Note: Maximum practical continuous power in an Adapter design with sufficient drain pattern as a heat sink, at 50°C
ambient.
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US3651

Preliminary
CMOS IC
ELECTRICAL CHARACTERISTICS (TA=25°C, VDD=15V, unless otherwise specified)
PARAMETER
SYMBOL
TEST CONDITIONS
MIN TYP MAX UNIT
SUPPLY SECTION
Turn-on Threshold Voltage
VTH(ON)
13.5 14.5 16
V
Turn-off Threshold Voltage
VTH(OFF)
8.2
9
10.5
V
VDD OVP Protection
VDD_OVP
28
V
Startup Current
IDD-ST
5
20
μA
Operating Current
IDD-OP
1.6
2
mA
Green-Mode Operating Current
IDD-GREEN
1.3
mA
OSCILLATOR SECTION
Maximum Frequency
fOSC
55
65
75
kHz
Minimum Frequency at CCM
fOSC-CM-MIN
17
kHz
Minimum Frequency at No-load
fOSC-N-MIN
370
Hz
Frequency Hopping Range
△f/freq
±5.0
%
Frequency Hopping Period
tFHR
3
ms
INV SECTION
Reference Voltage for EA
VVR
1.97 2.00 2.03
V
Reference Voltage for CCM
VVR_CCM
0.5
V
Max. Cable Compensation Current
ICABLE_MAX
37
uA
CURRENT SENSE SECTION
Current Sense Threshold Voltage
VCS
870 900 930 mV
OCP Propagation Delay
tD_OC
90
200
nS
Leading Edge Blank Time
tLEB
900
nS
Soft Start Time
tSS
10
mS
POWER MOSFET SECTION
MOSFET DS Breakdown Voltage
BVDSS
600
V
On Resistance
RDS(ON)
11
15
Ω
OTP SECTION
Threshold Temperature of OTP (Note)
TOTP
+140
°C
Note: When the over-temperature protection is activated, the power system enters auto restart mode and output is
disabled.
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US3651

Preliminary
CMOS IC
OPERATION DESCRIPTION
The UTC US3651 is a primary control switch mode charger and adapter applications. It operates in primary-side
sensing and regulation. Opto-coupler and TL431 could be eliminated. Proprietary built-in CV and CC control can
achieve high precision CV/CC performance. The device integrates PWM controller to enhance the performance of
discontinuous conduction mode (DCM) flyback converters.
Startup control
The VDD pin of UTC US3651 is connected to the line input through a resistor. A large value startup resistor can be
used to minimize the power loss in application because the start current of UTC US3651 is very low. When the VDD
voltage reaches VTH(ON), the internal startup circuit is disabled and the IC turns on.
Operating Current
The Operating current of UTC US3651 is as low as 1.6mA. Good efficiency and very low standby power can be
achieved.
Constant Voltage Operation
The output voltage is defined by the transmission ratio between the secondary and auxiliary winding. The UTC
US3651 captures the auxiliary winding feedback voltage at INV pin and operates in constant-voltage (CV) mode to
regulate the output voltage. The auxiliary voltage reflects the output voltage is given by:
VAUX =
NA
×(VO + ∆V)
NS
(1)
Where △V indicates the drop voltage of the output diode.
Figure 2. Auxiliary voltage waveform
Via a resistor divider connected between the auxiliary winding and INV, the VAUX is sampled at the Tsampling end
and it is hold until the next sampling. The sampled voltage is compared with 2.0V reference voltage and the error is
amplified. The error amplifier output reflects the load condition and controls the TOFF time and the Ipk to regulate the
output voltage, thus constant output voltage can be achieved.
Constant Current Operation
When the sampled voltage is below 2.0V reference voltage and the error amplifier output reaches its maximum,
thus UTC US3651 operates in constant-current (CC) mode. The CC point and maximum output power can be
externally adjusted by external current sense resistor Rcs. The larger Rcs, the smaller CC point is, and the smaller
output power becomes.
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US3651

Preliminary
CMOS IC
OPERATION DESCRIPTION(Cont.)
Large
Rcs
VOUT
Small
Rcs
IOUT
Figure 3. Adjustable output power by changing RCS
Figure 4. Secondary current waveform
In CC operation, the CC loop control function of UTC US3651 will keep a fixed proportion between secondary
inductance de-magnetization time (Tdemag) and switching cycle time (Tsw). The fixed proportion is
Tdemag 1
=
Tsw
2
(2)
Thus the output current is given by:
IOUT 
1
2

NP
NS
 IPK 
Tdemag
Tsw

1
4

NP
NS
 IPK
(3)
Programmable Cable Drop Compensation
UTC US3651 has a built-in cable voltage drop compensation to achieve good load regulation. An offset voltage is
generated at INV pin by an internal current flowing into the resistor divider. The current is inversely proportional to
the voltage of COMP pin. As a result, it is inversely proportional to the output load current. The voltage drop across
the cable is compensated by this offset voltage at INV pin. It can also be programmed by adjusting the resistance of
the divider to compensate the drop for various cable lines used.
Current Sensing and Leading Edge Blanking
Cycle-by-cycle current limiting is offered in UTC US3651. The switch current is detected by a sense resistor into
the CS pin. When the power switch is turned on, a turn-on spike will occur on this resistor. A 900ns leading-edge
blanking is built in to avoid false-termination of the switching pulse so that the external RC filtering is no longer
needed.
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US3651

Preliminary
CMOS IC
OPERATION DESCRIPTION(Cont.)
Protection Control
Good power supply system reliability is achieved with its comprehensive protection features including VDD
over-voltage protection, VDD Clamp, GATE Clamp, Power on soft start, Cycle-by-cycle current limiting, short circuit
protection, leading edge blanking, OTP and UVLO, etc.
VDD is supplied by transformer auxiliary winding output. The output of UTC US3651 is shutdown when VDD drops
below VTH(OFF) and the power converter enters power on start-up sequence thereafter.

TYPICAL APPLICATION CIRCUIT
L
Is
Vo
D1
N
NP
INV
VDD
DRAIN
NS
Co
Io
NA
UTC
US3651
COMP
CS
GND
RCS
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. The information
presented in this document does not form part of any quotation or contract, is believed to be accurate
and reliable and may be changed without notice.
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