MB3817_03 Datasheet, PDF (24/28 Pages) Fujitsu Component Limited. – Switching Regulator Controller

MB3817
s APPLICATION
1. Equivalent series resistance and stability of smoothing capacitor
The equivalent series resistance (ESR) of the smoothing capacitor in the DC/DC converter greatly affects the
loop phase characteristic.
A smoothing capacitor with a high ESR improves system stability because the phase is advanced into the high-
frequency range of an ideal capacitor (see Fig. 34 and 35) . A smoothing capacitor with a low ESR reduces
system stability. Use care when using low ESR electrolytic capacitors (OS-CON^TM) and tantalum capacitors.
Note : OS-CON is the trademark of Sanyo Electric Co.,Ltd.
Figure 33 DC/DC Converter Basic Circuit
Tr
L
RC
VIN
D
RL
C
Figure 34 Gain vs. Frequency
20
0
−20
(2)
−40
(1) : RC = 0 Ω
(2) : RC = 31 mΩ
(1)
−60
10
100
1k
10 k
Frequency f (Hz)
100 k
Figure 35 Phase vs. Frequency
0
(2)
−90
(1) : RC = 0 Ω
(1)
(2) : RC = 31 mΩ
−180
10
100
1k
10 k
100 k
Frequency f (Hz)
24