Datasheet
SLUU166A - December 2003 − Revised February 2004
23
UCC39002 Advanced Load-Share Controller User’s Guide, HPA027A
Error Amplifier Compensation
System stability requires the load share circuit’s unity gain crossover frequency to be well before the unity gain
crossover frequency of the power module, as measured in the first step of this design. In order to compensate
the error amplifier so that the load share controller’s crossover frequency does not interfere with the power
module, a zero is added to the error amplifier at least one decade before the module’s crossover frequency. In
this design, because the module’s crossover frequency is relatively high, at 25.6 kHz, the zero can be easily
placed two decades before this. f
zero
is equal to the desired frequency of the error amplifier compensation zero:
f
ZERO
+
f
COMOD
100
f
ZERO
+ 256 Hz
The absolute value of the gain of the power module is calculated at this zero frequency from the equation used
to plot Figure 3, or it can be estimated from the original gain frequency measurement, note this value is unit less,
not in dB:
Ť
G
MOD
ǒ
f
ZERO
Ǔ
Ť
+ 691.784
A
V
is equal to the voltage gain:
A
V
+
R
SENSE
R
LOAD
R
LOAD
is equal to:
R
LOAD
+
V
OUT
I
OUT(max)
A
V
+ 4 10
*3
A
ADJ
is equal to the adjust amplifier gain:
A
ADJ
+
R
ADJ
500 W
A
ADJ
+ 0.027
G
M
is equal to the transconductance of the internal error amplifier:
G
M
+ 0.014 S
S +
1
W
Combine all of the gains to determine the appropriate capacitor for compensation, C
EAO
:
C
EAO
+
G
M
2 p f
ZERO
A
CSA
A
V
A
ADJ
Ť
G
MOD
ǒ
f
ZERO
Ǔ
Ť
C
EAO
+ 64.065 mF
Actual capacitor value used:
C
EAO
+ 68 mF
R
EAO
is equal to the series resistor used in the error amplifier compensation:
R
EAO
+
1
2 p f
ZERO
C
EAO