BD8963EFJ(2010) Ver la hoja de datos (PDF) - ROHM Semiconductor

Número de pieza

componentes Descripción

Fabricante

BD8963EFJ
(Rev.:2010)

Low Noise High-efficiency Switching Regulator with Built-in Power MOSFET

ROHM Semiconductor 

BD8963EFJ

Technical Note

4. Determination of RCOMP, CCOMP that works as a phase compensator

As the Current Mode Control is designed to limit a inductor current, a pole (phase lag) appears in the low frequency area

due to a CR filter consisting of a output capacitor and a load resistance, while a zero (phase lead) appears in the high

frequency area due to the output capacitor and its ESR. So, the phases are easily compensated by adding a zero to the

power amplifier output with C and R as described below to cancel a pole at the power amplifier.

A

Gain

[dB] 0

0

Phase

[deg]

-90

fp(Min.)

fp(Max.)

IOUTMin.

IOUTMax.

fz(ESR)

fp=

1

2π×RO×CO

fz(ESR)=

1

2π×ESR×CO

Pole at power amplifier

When the output current decreases, the load resistance Ro

increases and the pole frequency lowers.

fp(Min.)=

1

2π×ROMax.×CO

[Hz]←with lighter load

Fig.28 Open loop gain characteristics

fp(Max.)=

1

2π×ROMin.×CO

[Hz] ←with heavier load

A

Gain

[dB]

0

0

Phase

[deg]

-90

fz(Amp.)

Zero at power amplifier

Increasing capacitance of the output capacitor lowers the pole

frequency while the zero frequency does not change. (This is

because when the capacitance is doubled, the capacitor ESR

reduces to half.)

fz(Amp.)=

1

2π×RCOMP×CCOMP

Fig.29 Error amp phase compensation characteristics

VCC

Cin

L

EN

VCC

SW

VOUT

VOUT

ADJ

ESR

RO

COMP GND

CO

RCOMP

CCOMP

Fig.30 Typical application

Stable feedback loop may be achieved by canceling the pole fp (Min.) produced by the output capacitor and the load

resistance with CR zero correction by the error amplifier.

fz(Amp.)= fp(Min.)

1

2π×RCOMP×CCOMP

=

1

2π×ROMax.×CO

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© 2010 ROHM Co., Ltd. All rights reserved.

11/17

2010.06 - Rev.A

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