Datasheet

SLUU166A - December 2003 − Revised February 2004
19
UCC39002 Advanced Load-Share Controller User’s Guide, HPA027A
100 1000 10000 100000
−200
−150
−100
−50
0
PHASE
vs
FREQUENCY
Phase − Degrees
Frequency − Hz
Figure 12. Phase-Frequency Mathematical Approximation of the PT4484 Module
Choosing the Sense Resistor
Because the current sense resistor is in series with the sense lines of the module, the voltage drop across the
sense resistor, V
RSENSE
, must be subtracted from the maximum voltage adjustment range of the module.
V
RSENSE
must be much less than ∆V
ADJ
otherwise there would be no headroom for the load share controller
to adjust the output voltage of the module. The following equation should be true:
R
SENSE
I
OUT(max)
t DV
ADJ
The evaluation module can accommodate two 1-W resistors in parallel for each load share controller circuit. In
order to allow for de-rating, the maximum combined power dissipation is limited to 1 W for the combination.
P
RSENSE(max)
is equal to the desired maximum power dissipation of the sense resistors:
P
RSENSE(max)
+ 1W
R
SENSE(max)
is equal to the maximum value of the current sense resistor for the given allowable power
dissipation:
R
SENSE(max)
+
P
RSENSE(max)
I
OUT(max)
2
R
SENSE(max)
+ 2.5 mW