MB3788 Просмотр технического описания (PDF) - Fujitsu

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MB3788

SWITCHING REGULATOR CONTROLLER

Fujitsu 

MB3788

s EQUIVALENT SERIES RESISTANCE OF SMOOTHING CAPACITOR AND STABILITY OF

DC/DC CONVERTER

The equivalent series resistance (ESR) of the smoothing capacity in a DC/DC converter has a great effect on the loop phase characteristics.

The ESR causes a small delay at the capacitor with a series resistance of 0 (Figures 8 and 9), thus improving system stability. On the other

hand, using a smoothing capacitor with a low ESR reduces system stability. Therefore, attention should be paid to using semiconductor electrolytic

capacitors (such as OS capacitors) or tantalum capacitors with a low ESP. (Phase margin reduction by using an OS capacitor is explained on

the next page.)

Tr

L

RC

VIN

D

RL

C

Fig. 7 Basic Voltage-Drop Type DC/DC Converter Circuit

20

0

Gain -20

(dB)

(2)

-40

(1): RC = 0 Ω

(2): RC = 31 mΩ

(1)

-60

101001 k 10 k100 k

Frequency f (Hz)

Fig.8 Gain - Frequency Characteristic

0

(2)

Phase -90

(deg)

(1): RC = 0 Ω

(1)

(2): RC = 31 mΩ

-180

101001 k 10 k100 k

Frequency f (Hz)

Fig.9 Phase - Frequency Charecteristic

16

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