Advanced Analog Technology, Inc.
Vo 2πfciCRcs
(
RL + 2rc
)
Rc =
VFB
kgm
⎡
⎤
r
(
1− D RL −
)
⎢
⎣
⎥
⎦
(
1− D
)
VFB is equal to reference voltage,VREF
.
VREF =1.24V, k is the correct factor, and
k = (6 − 8)
5. The output filter capacitor is chosen so C .
RL pole cancels Rc .Cc zero
R
C
⎛
⎜
⎞
L
RcCc =
Cc =
+ r , and
⎟
c
(
1− 3
)
2
⎝
⎠
⎞
R
C
⎛
L
+ rc
⎜
⎟
⎠
Fig.5. Bode diagram using Matlab simulation
(
)
1− 3 Rc
2
⎝
Example:
VIN =5V, VO =9.6V, IO =250mA, fs =600 kHz,
VFB =1.25V, L = 6.8uH , gm = 105uS , Rcs = 0.275
V/A, rL = 0.1Ω , rDS = 0.23Ω, r = 50mΩ , k =7
C
RF = 1.4Ω, fci = 21.4 kHz, Cc =1.3nF, Rc = 27k
Ω, C =4.7uF
Fig.4. CH1: PWM waveform, CH2, vp− p
for Vo
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