MB3817 Datasheet, PDF (22/29 Pages) Fujitsu Component Limited. – Switching Regulator Controller

MB3817
(Reference Data)
The phase margin is halved by changing the smoothing capacitor from an aluminium electrolytic capacitor (RC
~ _{1.0 Ω) to a small-ESR semiconductor electrolytic capacitor (OS – CON; RC} ~ _{0.2 Ω). (See Figure 5 and 6.)}
• Figure 4 DC/DC converter AV – φ characteristic measuring circuit
VOUT
VO ⁺
CNF
−IN
FB
+IN
AV − φ characteristic
between this interval
VIN
R2
R1
VREF
Error amp.
• Figure 5 Gain-Frequency characteristic
Gain - frequency and phase frequency characteristics of Al electrolytic capacitor (DC/DC converter +5 V output)
60
VCC = 10 V
40
AV
RL = 25 Ω
CP = 0.1 µF
180
φ
VO ⁺
20
90
+ Al electrolytic capacitor
0
62 °
0
220 µF (16 V)
− RC ≅ 1.0 Ω : FOSC = 1 kHz
−20
−90
GND
−40
10
100
1k
10 k
Frequency f (Hz)
−180
100 k
• Figure 6 Phase-Frequency characteristic
Gain - frequency and phase frequency characteristics of OS − CON (DC/DC converter +5 V output)
60
AV
40
20
0
VCC = 10 V
RL = 25 Ω
CP = 0.1 µF
180
90
φ
27 °
0
VO ⁺
+ OS − CON
22 µF (16 V)
− RC ≅ 0.2 Ω : fOSC = 1 kHz
−20
−90
GND
−40
10
100
1k
10 k
Frequency f (Hz)
−180
100 k
22