BD8158FVM(2010) Ver la hoja de datos (PDF) - ROHM Semiconductor

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fabricante

BD8158FVM
(Rev.:2010)

High-efficiency Step-up Switching Regulators with Built-in Power MOSFET

ROHM Semiconductor 

BD8152FVM, BD8158FVM

Technical Note

Description of Operation of Each Block

L1 10uH

D1

RB161M-20

VCC

C1

10uF

C2

0.01uF

8

SS

SLOPE

+

SOFT

START

7

FCLK

OSC

6

VCC

5

SW

CURRENT

SENSE

Set LOGIC DRV

Reset

SDW N

P+W-M

OCP

E- R+R

UVLO/TSD

1.245V

VREF

C0

10uF

VOUT

9V

COMP

1

FB

2

ENB

3

GND

4

C4 ＊

100pF

R3

5.1kΩ

C3

3300pF

R1

110kΩ

R2

18kΩ

Fig. 20 Application Circuit Diagram Example

 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.

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6/17

2010.03 - Rev.B

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