US3602

Preliminary

CMOS IC

UNISONICTECHNOLOGIESCO.,LTD

5 of 7

www.unisonic.com.tw

QW-R502-985.b



FUNCTION DESCRIPTION

The UTC US3602 is a primary side control offline LED lighting controller. It operates in inductor current DCM

mode and can achieve accurate constant current. The UTC US3602 integrates 600V power MOSFET and simplifies

the LED lighting system design by eliminating the secondary side feedback components and the opto-coupler. The

loop compensation components are also removed while maintaining stability overall operating conditions.

Startup control

Operating Current

The operating current of UTC US3602 is as low as 1mA. Good efficiency and very low standby power can be

achieved.

Constant Current Operation

When the FB voltage is over 1.2V reference voltage and the demagnetization time is lager than 4µS, thus UTC

US3602

operates in constant-current (CC) mode. The CC point can be externally adjusted by external current sense

resistor RCS.

In CC operation, the CC loop control function of UTC US3602 will keep a fixed proportion between secondary

inductance demagnetization time (Tdemag) and switching cycle time (Tsw). The fixed proportion is

2

1

=

Tsw

Tdemag

Thus the output current is given by:

Ipk

×

N

N

×

4

1

=

Tsw

Tdemag

×

Ipk

×

N

N

×

2

1

=

Iout

S

P

S

P

Figure4. Secondary current waveform

Current Sensing and Leading Edge Blanking

Cycle-by-cycle current limiting is offered in UTC US3602. 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.

Programmable Line Voltage Compensation

UTC US3602

has a built-in line voltage compensation to achieve good line regulation. An offset voltage is

generated at CS pin by a sense current from upper resistor at FB pin. The current is inversely proportional to the

upper resistor and is proportional to the line voltage. So the line voltage is compensated by this offset voltage at CS

pin. It can also be programmed by adjusting the resistance of the divider for various line voltage used.

The ratio of line compensation can be calculated by the equation:

=

V

)

mV

(

R

V

×

10

×

FBH

AUX

6