MB3778P Fujitsu Microelectronics, Inc., MB3778P Datasheet - Page 23

• Manufacturer Part Number: MB3778P
• Description: Switching Regulator Controller
• Manufacturer: Fujitsu Microelectronics, Inc.

1. Equivalent series resistor and stability of smoothing capacitor
Note: OS CON is the trademark of Sanyo Electnic Co., Ltd.
APPLICATION
The equivalent series resistor (ESR) of the smoothing capacitor in the DC/DC converter greatly affects the loop
phase characteristic.
The stability of the system is improved so that the phase characteristic may advance the phase to the ideal
capacitor by ESR in the high frequency region (see “Gain vs. Frequency” and “Phase vs. Frequency”).
A smoothing capacitor with a low ESR reduces system stability. Use care when using low ESR electrolytic
capacitors (OS CON
20
20
40
60
0
10
(1) R
(2) R
C
C
V
Gain vs. Frequency
100
IN
0
31 m
TM
Frequency f (Hz)
) and tantalum capacitors.
1 k
Tr
10 k
DC/DC Converter Basic Circuit
(1)
D
(2)
100 k
L
180
90
0
10
(1) R
(2) R
C
Phase vs. Frequency
C
C
R
100
C
0
31 m
Frequency f (Hz)
1 k
R
L
10 k
MB3778
(1)
(2)
100 k
23