BD8312HFN

Technical Note

11/14

www.rohm.com

2010.06- Rev.C

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

[2] Cs and Rs setting

For DC/DC converter, the 2nd dimension pole point is caused by the coil and capacitor as expressed by the following

equation.

This secondary pole causes a phase rotation of 180°. To secure the stability of the system, put a zero point in 2 places to

perform compensation.

Zero point by built-in CR

= 13kHz

Zero point by Cs

Those pole points are summarized in the figure below. The actual frequency property is different from the ideal

calculation because of part constants. If possible, check the phase margin with a frequency analyzer or network analyzer.

Otherwise, check for the presence or absence of ringing by load response waveform and also check for the presence or

absence of oscillation under a load of an adequate margin.

2π√(LC)

1

・・・・

(4)

1

(5)

・・・・

(5)

・・・・

(6)

(6)

(4)

(3)

1

Fig.35 Example of DC/DC converter frequency property

（

Measured with FRA5097 by NF Corporation）