UD36241

Preliminary

CMOS IC

UNISONICTECHNOLOGIESCO.,LTD

6 of 7

www.unisonic.com.tw

QW-R115-022 a



APPLICATION INFORMATION

Application information

The UD36241 is a constant frequency, current mode asynchronous step-down converter with CC and CV control.

In normal operation, the high side N-MOSFET is turned on when the S-R latch is set by the oscillator and is turned

off when the current comparator resets the S-R latch. While the N-MOSFET is turned off, the inductor current

conducts through the external diode.

Error Amplifier

After the system is powered up, the input voltage is charged on the OUT pin through the depleted MOS, and when the

OUT. The error amplifier adjusts its output voltage by comparing the feedback signal (VFB) with the internal 1V reference.

When the load current increases, it causes a drop in the feedback voltage relative to the reference, the error amplifier's

output voltage then rises to allow higher inductor current to match the load current

Oscillator

The internal oscillator runs at fixed frequency 100kHz. In short circuit condition, the controller is turn off the power

MOSFET for low power consumption.

Internal Regulator

The regulator provides low voltage power to supply the internal control circuits and the bootstrap power for

high side gate driver.

Over temperature adjustment function

UD36241

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,

Enable

The converter is turned on when the EN pin is higher than 2V and turned off when the EN pin is lower than 0.3V.

Attach this pin to VIN with a 100k pull up resistor for automatic startup

Soft-Start (SS)

An internal current source charges an internal capacitor to build a soft-start ramp voltage. The FB voltage will track

the internal ramp voltage during soft-start interval. The typical soft-start time is 1.2ms.

Output Line Drop Compensation

If the trace from UD36241 output terminator to the load is too long, there will be a voltage drop on the long trace

which is variable with load current. UD36241 is capable of compensating the output voltage drop to keep a constant

voltage at load, whatever the load current is. The output voltage is compensated by feeding a current to the top

feedback resistance R1. The load line compensation gain can be programmed according to RSENSE and Rtrace

values.

RSENSE

R1

Rtrace2

IOUT

VLOAD

R2

CSP

CSN

FB

Rtrace1

IOUT × RSENSE × 20μ × R1=IOUT × Rtrace

Rtrace

R1=

20μ×RSENSE