MB3782_1 Datasheet, PDF (22/27 Pages) Fujitsu Component Limited. – ASSP Power Supplies BIPOLAR Switching Regulator Controller

MB3782
s APPLICATIONS
• Concerning Equivalent Series Resistance and Stability of Smoothing Capacitors
In DC/DC converters, the equivalent series resistance value (ESR) of smoothing capacitors has a major influence
on loop phase characteristics.
The ESR is a means by which phase characteristics approximate phase relationships to ideal capacitors in high-
frequency bands (see Graph 1), thus improving system stability. At the same time, the use of smoothing capacitors
with low ESR reduces system stability, so that care must be taken when using semiconductor electrolytic ca-
pacitors (OS capacitors) or tantalum capacitors with low ESR.
L
Tr
Rc
VIN
D
RL
C
Figure 7 Basic circuit for step-down voltage DC/DC converter
Frequency vs.Gain
20
Frequency vs.phase
0
0
– 20
2
– 40
1 : Rc = 0 Ω
1
2 : Rc = 31 mΩ
– 60
10
100
1k
10 k
Frequency f (Hz)
100 k
2
– 90
1 : Rc = 0 Ω
1
2 : Rc = 31 mΩ
– 180
10
100
1k
10 k
100 k
Frequency f (Hz)
Graph 1 Frequency vs. gain and phase
22