Rainbow Electronics MAX8724 - Manual (Page 23)

the charge-current amplifier transconductance = 1µA/mV.
GM
IN is the DC-DC converter transconductance =
3.3A/V. The CCS loop is a single-pole system with a dom-
inant pole compensation set by f
P_CS :
The loop transfer function is given by:
Since:
Then, the loop transfer function simplifies to:
The crossover frequency is given by:
The CCS loop dominant compensation pole:
where the GMS amplifier output impedance, R OGMS =
10MΩ.
To calculate the CCI loop compensation pole, C
CS :
GMS = 1µA/mV
GM
IN
= 3.33A/V
R OGMS = 10MΩ
f = 400kHz
f
R C
P CS
OGMS CS
_
=
×
1
2π
f
GMS
C
CO CS
CS
_
=
2π
LTF GMS
R
sR C
OGMS
OGMS CS
= Ч
+ Ч 1
GM
A RS
IN
CSS
=
×
1
1
LTF GM A RS GMS
R
sR C
IN CSS
OGMS
OGMS CS
= Ч Ч Ч Ч
+ Ч
1
1
f
R C
P CS
OGMS CS
_
=
×
1
2π
MAX1908/MAX8724
Low-Cost Multichemistry Battery Chargers
______________________________________________________________________________________ 23
GM
IN
CCS
GMS
CLS
C CS
R
OGMS
CSSP CSSN
CSS
RS1
Figure 9. CCS Loop Diagram
CCS 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
CCS 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 10. CCS Loop Gain/Phase vs. Frequency