ISL6264 Datasheet, PDF (23/24 Pages) Intersil Corporation – Two-Phase Core Controller for AMD Mobile Turion CPUs

ISL6264
In the above example, the two errors add to 4A. For the two
phase DC/DC, the currents would be 22A in one phase and
18A in the other phase. In the above analysis, the current
balance can be calculated with 2A/20A = 10%. This is the
worst case calculation, for example, the actual tolerance of
two 10% DCRs is 10%*sqrt(2) = 7%.
Fault Protection - Overcurrent Fault Setting
As previously described, the Overcurrent protection of the
ISL6264 is related to the Droop voltage. Previously we have
calculated that the Droop Voltage = ILoad * R_droop, where
R_droop is the load line slope specified as 2mV/A in the AMD
specification. Knowing this relationship, the over current
protection threshold can be set up as a voltage Droop level.
Knowing this voltage droop level, one can program in the
appropriate drop across the R_oc resistor. This voltage drop
will be referred to as V_oc. Once the droop voltage is greater
than V_oc, the PWM drives will turn off and PGOOD will go
low.
The selection of R_oc is given in Equation 21. Assuming we
desire an overcurrent trip level (Ioc) of 55A, and knowing
from the Intel Specification that the load line slope (R_droop) is
0.0021 (V/A), we can then calculate for R_oc as shown in
Equation 21.
R_OC
=
-^I-^O-----^C-----^â‹---^R-----^d---^r--^o----^o---^p-
10 µ A
=
5_----5_-----⋅_---0_---._--0_---0_---2_--
10 ⋅ 10^–6
=
11.5 k Ω
(EQ. 21)
Note, if the droop load line slope is not -0.002 (V/A) in the
application, the over current setpoint will differ from
predicted.
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FN6359.1
October 16, 2006