MB3775 Datasheet, PDF (18/25 Pages) Fujitsu Component Limited. – SWITCHING REGULATOR CONTROLLER

MB3775
2. Effect of equivalent series resistance 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 low ESR reduces system stability by increasing the phase shift in the high-frequency region (see Fig. 30).
Therefore, a smoothing capacitor with a high ESR will improve system stability. Be careful when using low ESR semiconductor electrolytic
capacitors (OS-CON) and tantalum capacitors.
Fig. 29 - Step Down DC/DC Converter Basic Circuit
L
Tr
RC
VIN
D
RL
C
Fig. 30 - Gain vs. Frequency
20
0
-20
(2)
-40
(1) : RC=0Ω
(2) ^{: RC=31mΩ}
-60
(1)
10
100
1K
10K
Frequency f(Hz)
100K
Fig. 31 - Phase vs. Frequency
0
(2)
-90
(1) : RC=0Ω
(1)
(2) ^{: RC=31mΩ}
-180
10
100
1K
10K
100K
Frequency f(Hz)
18