MB3785A_03 Datasheet, PDF (25/30 Pages) Fujitsu Component Limited. – Switching Regulator Controller (4 Channels plus High-Precision, High-Frequency Capabilities)

MB3785A
s APPLICATION
1. Equivalent series resistor and stability of smoothing capacitor
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^TM) and tantalum capacitors.
Note: OS-CON is the trademark of Sanyo Electnic Co., Ltd.
DC/DC Converter Basic Circuit
Tr
L
RC
VIN
D
RL
C
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
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)
25