Datasheet

SLUU166A - December 2003 − Revised February 2004
8
UCC39002 Advanced Load-Share Controller User’s Guide, HPA027A
Figure 3
100 1k 10k 100k
−50
0
50
100
−200
−100
−50
0
−150
GAIN AND PHASE
vs
FREQUENCY
Phase − Degrees
Gain − dB
Frequency − Hz
Phase
Gain
Figure 3 shows an example of the gain and phase frequency response measurement of a power module.
6.2 Choosing the Sense Resistor
The primary concern in the selection of the sense resistor, R
SENSE
, is to ensure that the sum of the voltage drops
across the resistor and the parasitic wire impedances, at maximum module output current, is significantly less
than the output voltage adjustment range of the modules, otherwise there would be no room for output voltage
adjustment.
I
OUT(max)
R
SENSE
tt DV
ADJ(max)
Other limitations for the sense resistor are the desired minimum power dissipation and available component
ratings. The board provided has space for two 1-W 2512 resistors in parallel to be used for current sensing, as
shown by R10 and R11 in Figure 1.
6.3 Setting the Gain of the Current Sense Amplifier
The gain of the current-sense amplifier (CSA) is configured by adding compensation components between the
inverting input to the amplifier, CS−, and the current sense amplifier output, CSO, of the load-share device. The
maximum voltage at the CSO pin, V
CSO(max)
, is limited by the saturation voltage of the internal current sense
amplifier and must be at least two volts less than VDD.
V
CSO(max)
t VDD * 2V
Referring to Figure 1, the CSA gain, A
CSA
, is equal to:
A
CSA
+
ǒ
R22
R19
Ǔ
+
V
CSO
ǒ
R
SENSE
I
OUT(max)
Ǔ
(1)
(2)
(3)