Справочник Пользователя для Fujitsu MB3788

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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.)

L

Tr

R

C

R

L

V

IN

D

C

20

0

-20

-40

-60

10

100

1k

10k

100k

0

-90

-180

10

100

1k

10k

100k

(2)

(1)

(1):  R

C

 = 0 

Ω

(2):  R

C 

= 31 m

Ω

(2)

(1)

Gain 

(dB)

Frequency f (Hz)

Frequency f (Hz)

Phase 

(deg)

(1):  R

C

 = 0 

Ω

(2):  R

C

 = 31 m

Ω

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

Fig.8  Gain - Frequency Characteristic

Fig.9  Phase - Frequency Charecteristic