BD9701FP/CP-V5/T/T-V5,BD9703FP/CP-V5/T/T-V5,BD9702CP-V5/T/T-V5

Technical Note

8/16

www.rohm.com

2009.04- Rev.B

© 2009 ROHM Co., Ltd. All rights reserved.

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Block Function Explanations

・

VREF

Generates the regulated voltage from VCC input, compensated for temperature.

・

OSC

Generates the triangular wave oscillation frequency using an internal resistors and capacitor. Used for PWM comparator input.

・

Error AMP

This block, via the INV pin, detects the resistor-divided output voltage, compares this with the reference voltage, then

amplifies and outputs the difference.

・

PWM COMP

Outputs PWM signals to the Driver block, which converts the error amp output voltage to PWM form.

・

DRIVER

This push-pull FET driver powers the internal Pch MOSFET, which accepts direct PWM input.

・

STBY

Controls ON/OFF operation via the STBY pin. The output is ON when STBY is High.

・

Thermal Shutdown (TSD)

This circuit protects the IC against thermal runaway and damage due to excessive heat. A thermal sensor detects the

junction temperature and switches the output OFF once the temperature exceeds a threshold value (175deg). Hysteresis

is built in (15deg) in order to prevent malfunctions due to temperature fluctuations.

・

Over Current Protection (OCP)

The OCP circuit detects the voltage difference between VCC and OUT by measuring the current through the internal Pch

MOSFET and switches the output OFF once the voltage reaches the threshold value. The OCP block is a self-recovery

type (not latch).

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Timing Chart

Error AMP OUTPUT

OUTPIN

OSC

(Internal Oscillation Wave)

OUTPUT

VCC PIN

VOLTAGE WAVE

VOLTAGE WAVE

VOLTAGE WAVE

Fig.29

Timing Chart