BD8179MUV-E2 查看數據表（PDF） - ROHM Semiconductor

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BD8179MUV-E2

5V Input Multi-channel System Power Supply IC

ROHM Semiconductor 

BD8179MUV

Technical Note

(4) Setting RC, CC of the Phase Compensation Circuit

In the current mode control, since the coil current is controlled, a pole (phase lag) made by the CR filter composed of the

output capacitor and load resistor will be created in the low frequency range, and a zero (phase lead) by the output

capacitor and ESR of capacitor will be created in the high frequency range. In this case, to cancel the pole of the power

amplifier, it is easy to compensate by adding the zero point with CC and RC to the output from the error amp as shown in

the illustration.

Open loop gain characteristics

A

Gain 0

[dB]

f p( Min)

fp(Max)

lOUTMin

lOUTM ax

0

Phase

[deg] -90

Error amp phase

compensation characteristics

A

Gain

[dB]

0

Phase 0

[deg] -90

Fig. 16 Gain vs Phase

fz (ESR)

Fp =

1

[Hz]

2 π  RO  CO

fz(ESR) =

1

2π ESR  CO

[Hz]

Pole at the power amplification stage

When the output current reduces, the load resistance

Ro increases and the pole frequency lowers.

fp(Min) =

1

2   ROMax  CO

[Hz]←at light load

fz(Max) =

1

2   ROMin  CO

[Hz]←at heavy load

Zero at the power amplification stage

When the output capacitor is set larger, the pole

frequency lowers but the zero frequency will not

change. (This is because the capacitor ESR

becomes 1/2 when the capacitor becomes 2 times.)

fp(Amp.) =

1

[Hz]

2   Rc  Cc

L

Vo

VCC

Cin

Rc

V cc,P Vcc

COMP

SW

GND,PGND

ESR

Ro

Co

Cc

Fig. 17 Application Circuit Diagram

It is possible to realize the stable feedback loop by canceling the pole fp(Min.), which is created by the output capacitor

and load resistor, with CR zero compensation of the error amp as shown below.

fz(Amp.) = fp(Min.)

1

2 π  Rc  Cc

-

1

2π Romax  C

[Hz]

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9/12

2009.07 - Rev.B

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