MB3785A Datasheet, PDF (25/29 Pages) Fujitsu Component Limited. – Switching Regulator Controller (4 Channels plus High-Precision, High-Frequency Capabilities)

MB3785A
(Reference Data)
The phase margin is halved by changing the smoothing capacitor from an aluminum electrolytic capacitor (RC =
1.0 Ω) to a small-ESR semiconductor electrolytic capacitor (OS – CON; RC = 0.2 Ω). (See Figure 21 and 22.)
Figure 20. DC/DC Converter AV-φ Characteristic Measuring Circuit
VOUT
VO+
CNF
AV–ø characteristic
between this interval
–IN
+
FB
+IN
R2
VIN
–
R1
VREF/2
Error amp
Figure 21. Gain-Frequency Characteristic
Gain - frequency and phase frequency characteristics of Al electrolytic capacitor (DC/DC converter +5 V output)
60
40
20
0
–20
–40
10
VCC = 10 V
RL = 25 Ω ₁₈₀
AV
CP = 0.1 µF
ϕ
90
62°
0
–90
100
1k
10 k
Frequency f (Hz)
–180
100 k
VO+
+ Al electrolytic capacitor
220 µF (16 V)
– _{RC ≅ 1.0 Ω : FOSC = 1 kHz}
GND
Figure 22. Phase-Frequency Characteristic
Gain - frequency and phase frequency characteristics of OS – CON (DC/DC converter +5 V output)
60
40
AV
20
0
VCC = 10 V
RL = 25 Ω ₁₈₀
CP = 0.1 µF
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
25