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Número de pieza US1651
Descripción PRIMARY-SIDE REGULATION PWM POWER SWITCH
Fabricantes Unisonic Technologies 
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UNISONIC TECHNOLOGIES CO., LTD
US1651
Preliminary
PRIMARY-SIDE REGULATION
PWM POWER SWITCH
CMOS IC
DESCRIPTION
The UTC US1651 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 US1651 operates in primary-side sensing and
regulation. Opto-coupler and TL431 could be eliminated. It
operates in fixed frequency mode at large load conditions,
frequency reduction mode at light/medium load and ‘Extended
burst mode’ at No/light load conditions. So that low standby power
can be achieved.
The UTC US1651 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.
SOP-8
FEATURES
* Programmable CV and CC regulation
* Primary-side sensing and regulation with No TL431 and
opto-coupler
* Multi-mode operation for high efficiency
* Adjustable constant current and output power setting
* Power on soft-start time (4ms)
* Frequency shuffling and adjustable gate drive greatly
improving EMI
* ”Extended burst mode control” for improved efficiency
and minimum standby design
* Built-in leading edge blanking (LEB)
* VDD under voltage lockout
* VDD over voltage shutdown and clamp
* Cycle-by-Cycle current limiting
* Fail-safe protection for open loop fault condition
* Auto-restart in over voltage condition
ORDERING INFORMATION
Ordering Number
US1651G-S08-R
Package
SOP-8
Packing
Tape Reel
www.unisonic.com.tw
Copyright © 2015 Unisonic Technologies Co., Ltd
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US1651 pdf
US1651
Preliminary
CMOS IC
OPERATION DESCRIPTION (Cont.)
Constant Current Operation
When INV lower than 1.25V, the system works in CC control, In CC operation, the CC point and maximum output
power can be externally adjusted by external current sense resistor Rcs. The larger Rcs, the saller CC point is, and
the smaller output power becomes, and vice versa as shown in Fig.2.
VO Large RS
Small RS
Fig 2. Adjustable output power by changing RS
IO
In charger applications, a discharged battery charging starts in the CC portion of the curve until it is nearly full
charged and smoothly switches to operate in CV portion of the curve.
In an AC/DC adapter, the normal operation occurs only on the CV portion of the curve. The CC portion provides
added cycle-by-cycle current limiting protection.
Extended Burst Mode Operation
At light load or zero load condition, most of the power dissipation in a switching mode power supply is from
switching loss, the core loss of the transformer and the loss on the snubber circuit. The magnitude of power loss is in
proportion to the switching frequency. Lower switching frequency leads to the reduction on the power loss and thus
conserves the energy.
The UTC US1651 self adjusts the switching frequency according to the loading condition. The switch frequency is
reduced at light/no load condition to improve the conversion efficiency. At light load/no load condition, the output of
the Error amplifier (EA) drops below the burst mode threshold level and device enters Burst Mode control. The
frequency control also eliminates the audio noise at any loading conditions.
Operation switching frequency
The switching frequency of UTC US1651 is internally set and adjusted according to CC/CV operation. No
external frequency setting components are required.
Frequency shuffling for EMI improvement
The frequency Shuffling/jittering (switching frequency modulation) is implemented in UTC US1651. The
oscillation frequency is modulated with a pseudo random source so that the tone energy is spread out. The spread
spectrum minimizes the conduction band EMI and therefore eases the system design.
Current Sensing and Leading Edge Blanking
Cycle-by-cycle current limiting is offered in UTC US1651. 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 500ns leading-edge
blanking is built in to avoid false-termination of the switching pulse so that the external RC filtering is no longer
needed.
UNISONIC TECHNOLOGIES CO., LTD
www.unisonic.com.tw
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