ISL6260CCRZ Datasheet, PDF (27/28 Pages) Intersil Corporation – Multiphase PWM Regulator for IMVP-6+ Mobile CPUs

ISL6260C
10uA
OC
-
+
Internal to
ISL6260
+
1
+
-
Σ
+
1
+
-
OCSET
Voc
Roc
+
DROOP
-
VSUM
DFB
VSUM
DROOP
+
VN
-
VDIFF
RTN
VSEN VO'
VO'
RS _EQV
=
RS
N
Vrsense_EQV
=
Iout ×
Rsense
N
RO_EQV
=
RO
N
FIGURE 48. EQUIVALENT MODEL FOR DROOP AND DIE SENSING USING DISCRETE RESISTOR SENSING
Figure 36, when the CPU is at 2.5A load, PMON can still
sink 0.6mA current. This allows the RC filter capacitor to
discharge when the CPU is at low current, thus providing
correct average power information on the capacitor.
Fault Protection - Overcurrent Fault Setting
As previously described, the overcurrent protection of the
ISL6260C is related to the Droop voltage. Previously we
have calculated that the Droop Voltage = ILoad * Rdroop,
where Rdroop is the load line slope specified as 0.0021
(V/A) in the Intel IMVP-6+ specification. Knowing this
relationship, the overcurrent 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
Roc resistor. This voltage drop will be referred to as Voc.
Once the droop voltage is greater than Voc, the PWM drives
will turn off and PGOOD will go low.
The selection of Roc is given below in Equation 23.
Assuming we desire an overcurrent trip level, Ioc, of 55A,
and knowing from the Intel Specification that the load line
slope, Rdroop is 0.0021 (V/A), we can then calculate for Roc
as shown in Equation 23.
Roc
=
I_---o_---c_-----×_-----R_-----d_---r_---o_----o_---p_--
10 μ A
=
-⁵---⁵-----^×----⁰----^.-⁰----⁰---²---¹--
10 x 10 ^–6
=
11.5 k Ω
(EQ. 23)
Note, if the droop load line slope is not -0.0021 (V/A) in the
application, the overcurrent setpoint will differ from
predicted.
A capacitor may be added in parallel with Roc to improve
noise rejection but the Roc*capacitor time constant cannot
exceed 20µs. Do not remove Roc if overcurrent protection is
not desired. The maximum Roc is 30k.
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27
FN9259.3
June 21, 2010