MB39A125 Datasheet, PDF (38/64 Pages) Fujitsu Component Limited. – DC/DC Converter IC for Charging Li-ion Battery

MB39A125/126
■ PHASE COMPENSATION
• Example Circuit
VIN
<Error Amp 3>
−INE3
16 −
Cc
+
4.2 V
Rc
FB123
15
VCC
21
<PWM Comp.>
<OUT>
+
OUT
Drive
20
−
−2.5V
−1.5V
VH
19
VH ^{(VCC − 6V)}
OSC
Bias
Voltage
Lo : Inductance
RL : Equivalent series resistance of inductance
Co : Capacity of condenser
ESR : Equivalent series resistance of condenser
Ro : Load resistance
RS2
15mΩ
Lo RL
I1
VBATT
RS1
33 mΩ
Ro
Rin1
Co
ESR
Rin2
• Frequency Characteristics of LC filter
Frequency characteristic of power output LC filter
(DC gain is included.)
90
80
70
gain
phase
180
160
140
60
120
50
100
40
Gain
80
30
60
20
40
10
20
0
0
−10
−20
−20
−40
−30
−60
−40 ^Phase
−80
−50
−100
−60
−120
−70
−140
−80
−160
−90
−180
1 10 100 1k 10k 100k 1M 10M
Frequency [Hz]
Cut-off frequency
f1 (Hz) =
2π
1
(Ro + ESR)
Lo × Co ×
(Ro ⁺ RL)
Lo = 15 µH
Co = 14.1 µF
Ro = 4.2 Ω
RL = 30 mΩ
ESR = 100 mΩ
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