MB39A119 Datasheet, PDF (26/53 Pages) Fujitsu Component Limited. – DC/DC Converter IC of Synchronous Rectification for charging Li-ion battery

MB39A119
■ PHASE COMPENSATION
Circuit example of phase compensation is shown below.
• Circuit example of phase compensation
VIN
<Error Amp3>
−INE3
−
+
Cc
Rc
FB123
4.2 V
<PWM Comp.>
<OUT>
+
Drive
−
VCC
OUT
OSC
−2.5 V
VH
−1.5 V _(VCC-6V)
VH
Bias
Voltage
RS2
15 mΩ
Lo RL
Co
l1
VBATT
RS1
Ro
33 mΩ
Rin1
ESR
Rin2
Lo : Inductance
RL : Equivalent series resistance of inductance
Co : Capacity of condenser
ESR : Equivalent series resistance of condenser
Ro : Load resistance
• Method to obtain frequency characteristic of LC filter
Frequency characteristic of power output LC filter
(DC gain is included.)
90
80
70
60
50
40
30
20
10
0
−10
−20
−30
−40
Phase
−50
−60
−70
−80
−90
gain
phase
Gain
180
160
140
120
100
80
60
40
20
0
−20
−40
−60
−80
−100
−120
−140
−160
−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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