Rainbow Electronics MAX8724 - Manual (Page 22)

MAX1908/MAX8724
The crossover frequency is given by:
The CCI loop dominant compensation pole:
where the GMI amplifier output impedance, R OGMI =
10MΩ.
To calculate the CCI loop compensation pole, C CI :
GMI = 1µA/mV
GM OUT = 3.33A/V
R OGMI = 10MΩ
f = 400kHz
Choose crossover frequency f
CO_CI
to be 1/5th the
MAX1908/MAX8724 switching frequency:
Solving for C CI , C CI = 2nF.
To be conservative, set C
CI
= 10nF, which sets the
crossover frequency at:
The compensation pole, f P_CI is set at:
CCS Loop Definitions
Compensation of the CCS loop depends on the parame-
ters and components shown in Figure 9. C
CS is the CCS
loop compensation capacitor. A CSS is the internal gain of
the current-sense amplifier. RS1 is the input current-
sense resistor, RS1 = 10mΩ. R
OGMS is the equivalent
output impedance of the GMS amplifier ≥ 10MΩ. GMS is
f
GMI
R C
Hz
P CI
OGMI CI
_
. =
×
=
2
0 0016
π
f
GMI
nF
kHz
CO CI _
= =
2 10
16
π
f
GMI
C
kHz
CO CI
CI
_
= =
2
80
π
f
R C
P CI
OGMI CI
_
=
×
1
2π
f
GMI
C
CO CI
CI
_
=
2π
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GM
OUT
CCI
GMI
ICTL
C CI
R
OGMI
CSIP CSIN
CSI
RS2
Figure 7. CCI Loop Diagram
CCI LOOP GAIN
vs. FREQUENCY
FREQUENCY (Hz)
GAIN (dB)
100k 10k 1 10 100 1k
-40
-20
0
20
40
60
80
100
-60
0.1 1M
CCI LOOP PHASE
vs. FREQUENCY
FREQUENCY (Hz)
PHASE (DEGREES)
100k 10k 1k 100 10 1
-90
-75
-60
-45
-30
-15
0
-105
0.1 1M
Figure 8. CCI Loop Gain/Phase vs. Frequency