UCSR3651SG-S08-R datasheet(6/9 Pages) UTC

6 / 9 page

UCSR3651S

Preliminary

CMOS IC

UNISONICTECHNOLOGIESCO.,LTD

6 of 9

www.unisonic.com.tw

QW-R129-010.d



OPERATION DESCRIPTION

The UTC UCSR3651S 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 UCSR3651S 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 UCSR3651S 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 UCSR3651S 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

UCSR3651S

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:

）

（

∆

AUX

(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.

UCSR3651SG-S08-R Datasheet(PDF) 6 Page - Unisonic Technologies