ROHM BD9870FPS Technical data

Single-chip Type with Built-in FET Switching Regulator Series

Simple Step-down
Switching Regulator
with Built-in Power MOSFET

BD9870FPS

● Description
The BD9870FPS single-channel step-down switching regulator incorporates a Pch MOSFET capable of PWM operation at
900kHz, enabling use of a smaller coil, as well as circuitry that eliminates the need for external compensation – only a diode,
coil, and ceramic capacitor are required – reducing board size significantly.

●Features

1) Maximum switching current: 1.5A

2) 2. Built-in Pch FET ensures high efficiency

3) Output voltage adjustable via external resistors

4) High switching frequency: 900kHz (fixed)

5) Soft start time: 5ms (fixed)

6) Overcurrent and thermal shutdown protection circuits built in

7) ON/OFF control via STBY pin

8) Ceramic output capacitor compatibility

9) Small surface mount TO252S-5 package

●Applications
TVs, printers, DVD players, projectors, gaming devices, PCs, car audio/navigation systems, ETCs, communication
equipment, AV products, office equipment, industrial devices, and more.

●Absolute Maximum Ratings（Ta＝25℃）

Parameter Symbol Ratings Unit
Supply Voltage（VCC-GND） Vcc 36 V
STBY-GND V
OUT-GND V
INV-GND V
Maximum Switching Current Iout 1.5
Power Dissipation Pd 800
Operating Temperature Topr -40 to +85 ℃
Storage Temperature Tstg -55 to +150 ℃

(*1) Do not exceed Pd, ASO, and Tjmax=150℃
(*2) Derated at 6.4mW/°C over Ta=25℃

●Operating Conditions(Ta=-40 to +85℃)
Parameter Symbol

Input Voltage VCC 8.0 35.0 V
Output Voltage Vo 1.0 0.8×(VCC-Io×Ron) V

36 V

STBY

36 V

OUT

5 V

INV

MIN MAX

(*1)

A

(*2)

mW

Limit

No.09027EAT26

Unit

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

1/11

2009.05 - Rev.A

BD9870FPS

Technical Note

●Electrical Characteristics（Unless otherwise noted, Ta=25℃,Vcc=12V,Vo=5V,STBY=3V）

Parameter Symbol

MIN TYP MAX

Limit

Unit Conditions

Output ON Resistance Ron - 1.0 1.5 Ω
Efficiency η 80 88 - % Io＝0.5A
Switching Frequency fosc 810 900 990 kHz

Load Regulation ΔVOLOAD - 5 40 mV

Vcc=20V,
Io=0.5 to 1.5A

Line Regulation ΔVOLINE - 5 25 mV Vcc=10 to 30V, Io=1.0A
Over Current ProtectionLimit Iocp 1.6 - - A
INV Pin Threshold Voltage VINV 0.99 1.00 1.01 V
INV Pin Input Current IINV - 1 2 μA VINV=1.0V

STBY Pin Threshold
Voltage

ON VSTBYON 2.0 - 36 V

OFF VSTBYOFF -0.3 - 0.3 V
STBYPin Input Current Istby 5 15 30 μA STBY=3V
Circuit Current Icc - 5 12 mA INV=2V
Stand-by Current Ist - 0 5 μA STBY＝0V
Soft Start Time Tss 1 4 10 ms

* This product is not designed to be resistant to radiation.

●Block Diagram

VCC

1

VREF

PWM

COMP

DRIVER

STBY

5

OSC

STBY

TSD

CTL

LOGIC

OCP

OUT

2

Error AMP

INV

4

FIN

GND

SS

Fig.1

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

2/11

2009.05 - Rev.A

BD9870FPS

●Package Dimensions

●Pin Description

Pin No. Pin Name Function

1 VCC
2 OUT

3※ OUT

FIN GND

4 INV
5 STBY

※Normally OPEN

Technical Note

TO252S-5（Unit：mm）

Fig.2

Input Power Supply Pin
Internal Pch FET Drain Pin
Internal Pch FET Drain Pin
Ground
Output Voltage Feedback Pin
ON/OFF Control Pin

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

3/11

2009.05 - Rev.A

BD9870FPS

●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.

Technical Note

●Notes for PCB layout

• 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.）

R2:1kΩ

1

C2

C3

R1:4kΩ

4

INV

VCC OUT

GND

FIN

STBY

Fig.3

5

L1

2

5.0V

C1

D1

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

4/11

2009.05 - Rev.A