UL98C

Preliminary

CMOS IC

UNISONICTECHNOLOGIESCO.,LTD

6 of 7

www.unisonic.com.tw

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APPLICATION INFORMATION

Application information

UL98C

is a constant current driver IC for LED lighting, which is applied to the non isolated LED driver power

supply.

The 500V power switch is integrated in the chip, which is based on the constant current architecture and control

method, and it can achieve excellent constant current characteristics with minimal external components.

And without auxiliary winding power supply and testing, the system cost is very low.

Start

voltage reaches the threshold value, the chip's internal reference circuit begins to work. When the chip is working

normally, the required operating current is still through the supply of internal consumption.

Constant current control

The chip is detected the peak current, and the RCS resistance is connected to the input terminal of the peak

comparator, which is compared with the threshold voltage 0.6V. When the RCS voltage reaches the threshold, the

LED current is adjusted, and realized the constant current control.

Among them, RCS is a current sampling resistor.

The output of the comparator CS also includes a 500ns leading edge blanking time.

Protection function

UL98C

built in a variety of protection functions, including LED short-circuit protection, LED open circuit protection,

sampling circuit short-circuit protection, temperature regulation and protection, etc.

When LED short circuit, the system works in the 3 KHz low frequency, so the power consumption is very low.

Over temperature adjustment function

UL98C

has the function of over temperature adjustment, the output current is gradually reduced when the driving

power is over, so that the output power and temperature rise is controlled, the power supply is maintained at the set

value,

In order to improve the reliability of the system, the chip is internally set to adjust the temperature of the 140°C.

PCB design

In the design of PCB, you need to follow the following guidelines:

RCS resistor requires close to the CS pin of the chip

CS pin increases in the area of copper clad to improve chip cooling.