BD9870FPS-E2 Rohm Semiconductor, BD9870FPS-E2 Datasheet - Page 4

• Manufacturer Part Number: BD9870FPS-E2
• Description: IC REG SW STEP DOWN TO-252S-5
• Manufacturer: Rohm Semiconductor
• Type: Step-Down (Buck)r

Specifications of BD9870FPS-E2

• Internal Switch(s): Yes
• Synchronous Rectifier: No
• Number Of Outputs: 1
• Current - Output: 1.5A
• Frequency - Switching: 900kHz
• Voltage - Input: 8 ~ 35 V
• Operating Temperature: -40°C ~ 85°C
• Mounting Type: Surface Mount
• Package / Case: DPak, TO-252 (Slim, 4 leads + tab)
• Power - Output: 800mW
• Input Voltage: 36 V
• Switching Frequency: 900 KHz
• Operating Temperature Range: -40 C to +85 C
• Mounting Style: SMD/SMT
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• Voltage - Output: -
• Lead Free Status / Rohs Status: Lead free / RoHS Compliant
• Other names: BD9870FPS-E2TR

●Block Function Explanations
●Notes for PCB layout
BD9870FPS
© 2009 ROHM Co., Ltd. All rights reserved.
www.rohm.com
• Place capacitors between Vcc and Ground, and the Schottky diode as close as possible to the IC to reduce noise and
• Connect resistors between INV and Ground, and the output capacitor filter at the same Ground potential in order to stabilize
（If the patterning is longer or thin, it’s possible to cause ringing or waveform crack.）
maximize efficiency.
the output voltage.
・ VREF
・ OSC
・ Error AMP
・ PWM COMP
・ DRIVER
・ STBY
・ Thermal Shutdown (TSD)
・ Over Current Protection (OCP)
・ Soft Start (SS)
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.
Generates the regulated voltage from Vcc input, compensated for temperature.
Generates the triangular wave oscillation frequency (900kHz) using an internal resistors and capacitor. Used for PWM
comparator input.
This block, via the INV pin, detects the resistor-divided output voltage, compares this with the reference voltage, then
amplifies and outputs the difference.
Outputs PWM signals to the Driver block, which converts the error amp output voltage to PWM form.
This push-pull FET driver powers the internal Pch MOSFET, which accepts direct PWM input.
Controls ON/OFF operation via the STBY pin. The output is ON when STBY is High.
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).
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.
R2:1kΩ
C2
1
VCC
INV
4
R1:4kΩ
C3
GND
FIN
Fig.3
4/11
STBY
OUT
2
5
D1
L1
C1
5.0V
Technical Note
2009.05 - Rev.A