BD8964FVM-TR 查看數據表（PDF） - ROHM Semiconductor

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BD8964FVM-TR

4.0V to 5.5V, 1.2A 1ch Synchronous Buck Converter with Integrated FET

ROHM Semiconductor 

BD8964FVM

Datasheet

(3) Selection of input capacitor (CIN)

Input capacitor must be a low ESR capacitor with a capacitance sufficient to

cope with high ripple current to prevent high transient voltage. The ripple current

VCC

CIN

IRMS is given by the equation (5):

VOUT

L

CO

Figure 28. Input Capacitor

  IRMS  IOUT

VOUT VCC VOUT

VCC

A・・・(6)

< Worst case > IRMSMax

When

VCC

is twice

the

VOUT , IRMS



IOUT

2

If VCC=5.0V, VOUT=1.5V, and IOUTMax=0.8A

IRMS  0.8 

1.55 1.5  0.37

5

ARMS 

A low ESR 10μF/10V ceramic capacitor is recommended to reduce ESR dissipation of input capacitor for better

efficiency.

(4) Calculating RITH, CITH for Phase Compensation

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

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

appears in the high frequency area due to the output capacitor and its ESR. Therefore, 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

A

Gain

[dB]

0

0

Phase

[deg]

-90

fp(Min)

fp(Max)

IOUTMin

IOUTMax

fZ(ESR)

fp



2



1

RO

 CO

fZ ESR



2



1

ESR

 CO

Pole at power amplifier

When the output current decreases, the load resistance RO

increases and the pole frequency decreases.

Figure 29. Open Loop Gain Characteristics

fZ(Amp)

fpMin 



2

1

 ROMax

 Co

fpMax 



2

1

 RO MIN

 Co

Hz  with lighter load

Hz  with heavier load

Zero at power amplifier

Increasing the 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 is reduced to half.)

fZ Amp



2

1

 RITH

 CITH

Figure 30. Error Amp Phase Compensation Characteristics

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