MB3782 Datasheet, PDF (24/28 Pages) Fujitsu Component Limited. – Switching Regulator Controller

MB3782
• Reference data
Changing the smoothing capacitor from an aluminum electrolytic capacitor (RC ≅ 1.0Ω) to a lower-ESR
semiconductor electrolytic capacitor (OS capacitor: RC ≅ 0.2 Ω) decreases the phase margin (see Graphs 1-2,
1-3).
V out
V0 ⁺
CNF
AV and phase characteristics
measured between these points
– IN
FB
–
+ IN
+
VIN
R2
R1
VREF/2
Error amp
Figure 2 Measurement of DC/DC Capacitor AV and Phase (Ψ) Characteristics
Graph
DC/DC converter + 5 V output frequency vs.gain and phase
60
40
Av
Vcc = 10 v
RL = 25 Ω
Cp = 0.1 µF ¹⁸⁰
φ
20
90
62°
0
0
– 20
– 90
– 40
– 180
10
100
1k
10 k
100 k
Graph 3
Frequency f (Hz)
DC/DC converter + 5 V output frequency vs.gain and phase
60
Av
40
Vcc = 10 v
RL = 25 Ω
Cp = 0.1 µF
180
20
90
φ
0
0
27°
– 20
– 90
– 40
– 180
10
100
1k
10 k
100 k
Frequency f (Hz)
24
V0 ⁺
Aluminum electrolytic
+ _capacitor
– _{220 µF (16 V)}
RC ≅ 1.0 Ω
: fosc = 1 kHz
+ ^{OS capacitor}
– ^{22 µF (16 V)}
RC ≅ 0.2 Ω
: fosc = 1 kHz