BD8152FVM, BD8158FVM

Technical Note

6/17

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2011.08 - Rev.C

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Description of Operation of Each Block

 Error amp (ERR)

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

duty is decided by the COMP pin voltage which is the comparison result. At the time of start, since the soft start is operated

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

 Oscillator (OSC)

This block generates the oscillating frequency. It is possible to select 600 kHz/1.2 MHz (Typ.) by the FCLK pin.

 SLOPE

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

the PWM comparator.

 PWM

Output COMP voltage of the error amp and the triangular waveform of the SLOPE block are compared to decide the

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

become 100%.

 Reference voltage (VREF)

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

 Protection circuit (UVLO/TSD)

UVLO (under-voltage lockout protection circuit) shuts down the circuits when the voltage is 2.2 V (TYP.BD8152FVM),1.8 V

(TYP.BD8158FVM) or lower. Thermal shutdown circuit shuts down IC at 175℃ (Typ.) and recovers at 160℃ (Typ.).

 Overcurrent protection circuit (OCP)

Current flowing to the power FET is detected by voltage at the CURRENT SENSE and the overcurrent protection operates

at 3 A (Typ.). When the overcurrent protection operates, switching is turned off and the SS pin capacity is discharged.

 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.

Fig. 20 Application Circuit Diagram Example

VCC

VOUT

UVLO/TSD

+

SENSE

CURRENT

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