BD8152FVM

BD8158FVM

Application Information

1. Description of Operation of Each Block

(1) Error Amp (ERR)

This is the circuit used to compare the reference voltage 1.245V(Typ) and the feedback voltage of output. Switching

duty is decided by the COMP pin voltage which is connected to the error amp output. During start-up, since the soft

start is operated by the SS pin voltage, the COMP pin voltage is limited to SS pin voltage.

(2) Oscillator (OSC)

(3) SLOPE

This block generates the triangular waveform from the clock generated by OSC. Generated triangular waveform is

fed to the PWM comparator.

(4) PWM

The output COMP voltage of the error amp and the triangular waveform of the SLOPE block are compared to set the

switching duty. Since the switching duty is limited by the maximum duty ratio which is set internally, it does not

become 100%.

(5) Reference Voltage (VREF)

This block generates the internal reference voltage of 1.245V(Typ).

(6) Protection Circuit (UVLO/TSD)

UVLO (under-voltage lockout protection circuit) shuts down the circuit when the voltage is equal or lower than

2.2V(Typ) for BD8152FVM and 1.8V(Typ) for BD8158FVM. Thermal shutdown circuit shuts down IC’s operation at

175°C(Typ) and recovers at 160°C (Typ).

(7) Over-Current Protection Circuit (OCP)

Current flowing to the power FET is detected by voltage at the CURRENT SENSE and the Over-Current protection

operates at 3A(Typ). When the Over-Current protection activates, the switching is turned OFF and the SS pin

capacity is discharged.

(8) Soft-Start Circuit

Since the output voltage rises gradually while restricting the current at the time of startup, it is possible to prevent the

output voltage overshoot or the inrush current.

VCC

VOUT

UVLO/TSD

+

SENSE

CURRE NT

1.245V

SW

VCC

GND

FCLK

SS

PWM

+

-

8

7

6

5

OSC

SLOPE

Set

DRV

SDWN

LOGIC

Reset

ERR

START

SOFT

1

2

3

4

COMP

FB

ENB

OCP

VREF

10uF

10uH

10uF

RB161M-20

C1

C2

0.01uF

C3

3300pF

R3

5.1kΩ

R1

110kΩ

R2

18kΩ

L1

D1

C0

9V

C4

100pF

10/23

TSZ02201-0323AAJ00550-1-2

© 2014 ROHM Co., Ltd. All rights reserved.

09.Sep.2014 Rev.001

www.rohm.com

TSZ22111・15・001