MB3782 Fujitsu Media Devices, MB3782 Datasheet - Page 23

• Manufacturer Part Number: MB3782
• Description: Switching Regulator Controller
• Manufacturer: Fujitsu Media Devices

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DataSheet
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3. Concerning Equivalent Series Resistance and Stability of Smoothing Capacitors
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.com
APPLICATIONS
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 1-1), 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 capacitors (OS capacitors) or tantalum capacitors with low ESR.
– 20
– 40
– 60
20
0
10
1 : Rc = 0
2
: Rc = 31 m
V
100
IN
Frequency vs.Gain
Frequency f (Hz)
Figure 1
1 k
Basic circuit for step-down voltage DC/DC converter
Tr
Graph 1
10 k
1
2
D
Frequency vs. gain and phase
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100 k
L
– 180
– 90
0
10
1 : Rc = 0
2
: Rc = 31 m
C
Rc
100
Frequency vs.phase
Frequency f (Hz)
1 k
R
L
MB3782
10 k
1
2
100 k
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