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