MAX8724 Maxim Integrated Products, MAX8724 Datasheet - Page 25

• Manufacturer Part Number: MAX8724
• Description: (MAX1908 - MAX87xx) Low-Cost Multichemistry Battery Chargers
• Manufacturer: Maxim Integrated Products

the charge-current amplifier transconductance = 1µA/mV.
GM
3.3A/V. The CCS loop is a single-pole system with a dom-
inant pole compensation set by f
The loop transfer function is given by:
Since:
Then, the loop transfer function simplifies to:
The crossover frequency is given by:
Figure 10. CCS Loop Gain/Phase vs. Frequency
LTF GM
IN
=
is the DC-DC converter transconductance =
IN
Low-Cost Multichemistry Battery Chargers
LTF GMS
×
f
P CS
A
_
=
100
-20
-40
-60
CSS
GM
80
60
40
20
0
______________________________________________________________________________________
f
CO CS
0.1
IN
=
×
_
RS
2π
×
=
1
1
1
R
A
+
×
=
OGMS
CSS
sR
GMS
10
2π
vs. FREQUENCY
CCS LOOP GAIN
GMS
R
FREQUENCY (Hz)
OGMS
1
1
P_CS
C
×
OGMS
100
CS
RS
×
×
1
C
:
1
+
1k
CS
×
sR
C
CS
R
OGMS
10k
OGMS
100k
×
C
1M
CS
The CCS loop dominant compensation pole:
where the GMS amplifier output impedance, R
10MΩ.
To calculate the CCI loop compensation pole, C
GMS = 1µA/mV
GM
R
f = 400kHz
Figure 9. CCS Loop Diagram
OGMS
-105
IN
-15
-30
-45
-60
-75
-90
0
= 3.33A/V
0.1
= 10MΩ
CCS
C
1
CS
f
P CS
10
CCS LOOP PHASE
_
vs. FREQUENCY
FREQUENCY (Hz)
R
OGMS
100
=
GM
2π
GMS
1k
IN
R
OGMS
10k
1
100k
CLS
CSSP
×
C
1M
CS
CSS
RS1
CSSN
CS
OGMS
:
25
=