BD9873CP-V5 Ver la hoja de datos (PDF) - ROHM Semiconductor

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Fabricante

BD9873CP-V5

Simple Step-down Switching Regulators

ROHM Semiconductor 

BD9873CP-V5,BD9874CP-V5

Technical Note

●Block Function Explanations

・ VREF

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

・ OSC

Generates the triangular wave oscillation frequency (900kHz) 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 (175°C).

Hysteresis is built in (15°C) 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).

・ Soft Start (SS)

This block conducts soft start operations. When STBY is High and the IC starts up the internal capacitor begins

charging. The soft start time is fixed at 5ms.

●Notes for PCB layout

C3：0.47uF

R2:1kΩ R1:4kΩ

4

INV

STBY 5

C1：100uF 1 VCC

C2：4.7uF

GND

3

OUT 2

L1：100uH

5.0V

D1

C4：680uF

Fig.3

• Place capacitors between Vcc and Ground, and the Schottky diode as close as possible to the IC to reduce noise and

maximize efficiency.

• Connect resistors between INV and Ground, and the output capacitor filter at the same Ground potential in order to stabilize

the output voltage.

（If the patterning is longer or thin, it’s possible to cause ringing or waveform crack.）

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

4/12

2009.07 - Rev.A

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