Document Number: 73578

S09-1456-Rev. B, 03-Aug-09

www.vishay.com

5

Vishay Siliconix

SiP12502

FUNCTIONAL BLOCK DIAGRAM

DETAILED OPERATION

SiP12502 is a 300 kHz boost converter IC, packaged in 6-pin

voltages as low as 0.65 V, this device features fixed

frequency voltage mode PWM control with internal frequency

this device maintains high efficiency over a wide range of

load currents. Under light load conditions, it switches to PFM

mode to maintain high efficiency. A power good signal is

available to monitor the output voltage.

Low Voltage Start-Up

SiP12502 is designed to start-up at input voltage of typically

the power source for its control logic and internal gate drive,

boost switch’s conduction interval during each cycle is

determined by the time taken for the inductor current to reach

internal current limit, followed by a fixed off time before the

exceeds 1.89 V, the device engages its built-in soft-start

circuitry.

Soft-Start

During soft-start, the loop compensation guarantees the slow

increase of output voltage, so that no large voltage overshoot

or inrush current transients occur when the soft-start period

ends.

PWM operation

After the soft-start interval is over, the device works in PWM

operation with a fixed frequency of 300 kHz, with automatic

switch-over to PFM operation during light load conditions.

PFM Operation

When operating into light loads, the SiP12502 automatically

switches to PFM operation. This reduces gate charge losses

in the boost switch, hence raising converter efficiency.

Over Voltage Protection

If the output voltage is above 10 % of the regulation voltage,

the device will turn off the internal power MOSFET and wait

until the output voltage falls below the regulation voltage,

then the PWM operation is enabled again.

Thermal Shutdown Protection

If the internal device temperature rises above 160 °C, the

device will turn off the internal power MOSFET. Once the die

temperature falls below 140 °C, the device performs a new

soft-start cycle, the converter resumes normal operation.

Antiringing Control

The antiringing control circuitry prevents high frequency

ringing at the LX pin as the inductor current goes to zero by

(capacitance on LX pin). When the IC is shutdown, this

antiringing switch is also turned on.