Datasheet

SLUU166A - December 2003 − Revised February 2004
10
UCC39002 Advanced Load-Share Controller User’s Guide, HPA027A
6.5 Error Amplifier Compensation
The total load-share loop must be configured for a unity gain crossover frequency well before the crossover
frequency of the module, f
COmodule
, as measured in Figure 2 and shown in Figure 3. This is accomplished by
placing a zero in the error amplifier compensation at least one decade before the module’s crossover frequency.
Compensation of the transconductance error amplifier is done by placing the compensation resistor, R
EAO
shown as R30 in Figure 1, and capacitor, C
EAO
shown as C12 in Figure 1, between EAO and GND. The values
of these components are determined by the following loop gain equation:
C
EAO
+
ǒ
G
M
2 p f
ZERO
Ǔ
A
CSA
A
V
A
ADJ
A
PWR(fco)
Where:
1. Gm is the transconductance of the error amplifier, typically 14 mS,
2. f
zero
is equal to the desired frequency in Hz of the zero to be added to the load-share loop, maximum zero
frequency will be equal to
f
CO(module)
10
,
3. A
CSA
equals R22/R19,
4. A
V
is the voltage gain, equal to
R
SENSE
R
LOAD
,
5. A
ADJ
is the gain associated with the adjust amplifier, equal to
R
ADJUST
500 W
,
6. A
PWR(f
CO
)
is the measured gain of the power module at the desired inserted zero frequency, read from
Figure 3 and converted from dB to V/V.
The calculated capacitor value will most likely be very large due to the low frequency of the zero. The actual
available capacitor used will undoubtedly be of a lower value and this must be taken into consideration when
determining the compensation resistor. Once the C
EAO
capacitor is determined, R
EAO
is selected to achieve
the desired loop response:
R
EAO
+
1
ǒ
2 p C
EAO(actual value used)
f
ZERO
Ǔ
(8)
(9)