ISL6377 Datasheet, PDF (27/36 Pages) Intersil Corporation – Multiphase PWM Regulator for AMD Fusion™ Desktop CPUs Using SVI 2.0

ISL6377
Table 13 summarizes the fault protections.
TABLE 13. FAULT PROTECTION SUMMARY
FAULT TYPE
FAULT DURATION
BEFORE
PROTECTION PROTECTION ACTION
FAULT
RESET
Overcurrent
7.5µs to 11.5µs PWM tri-state
Phase Current
Unbalance
Way-Overcurrent
(1.5xOC)
Undervoltage
-325mV
Overvoltage
+325mV
1ms
Immediately
PWM tri-state, PGOOD
latched low
PGOOD latched low.
PWM tri-state.
PGOOD latched low.
Actively pulls the output
voltage to below VID
value, then tri-state.
ENABLE
toggle or
VDD
toggle
NTC Thermal
100µs min PGOOD latched low.
PWM tri-state.
Fault Recovery
All of the previously described fault conditions can be reset by
bringing ENABLE low or by bringing VDD below the POR
threshold. When ENABLE and VDD return to their high operating
levels, the controller resets the faults and soft-start occurs.
Interface Pin Protection
The SVC and SVD pins feature protection diodes which must be
considered when removing power to VDD and VDDIO, but leaving
it applied to these pins. Figure 19 shows the basic protection on
the pins. If SVC and/or SVD are powered but VDD is not, leakage
current will flow from these pins to VDD.
SVC, SVD
INTERNAL TO
ISL6377
VDD
GND
FIGURE 19. PROTECTION DEVICES ON THE SVC AND SVD PINS
Key Component Selection
Inductor DCR Current-Sensing Network
PHASE1 PHASE2 PHASE3 PHASE4
R_SUM
RSUM
RSUM
RSUM
ISUM+
L
L
L
L
DCR DCR DCR DCR
RNTCS
RP
RNTC
RO
R_O
R_O
R_O
+
CNVCN
-
RI
ISUM-
IO
FIGURE 20. DCR CURRENT-SENSING NETWORK
Figure 20 shows the inductor DCR current-sensing network for a
4-phase solution. An inductor current flows through the DCR and
creates a voltage drop. Each inductor has two resistors in R_sum
and R_o connected to the pads to accurately sense the inductor
current by sensing the DCR voltage drop. The R_sum and R_o
resistors are connected in a summing network as shown, and feed
the total current information to the NTC network (consisting of
R_ntcs, R_ntc and R_p) and capacitor C_n. R_ntc is a negative
temperature coefficient (NTC) thermistor, used to temperature
compensate the inductor DCR change.
The inductor output side pads are electrically shorted in the
schematic but have some parasitic impedance in actual board
layout, which is why one cannot simply short them together for the
current-sensing summing network. It is recommended to use
1Ω~10Ω R_o to create quality signals. Since R_o value is much smaller
than the rest of the current sensing circuit, the following analysis
ignores it.
The summed inductor current information is presented to the
capacitor C_n. Equations 22 thru 26 describe the frequency
domain relationship between inductor total current I_o(s) and C_n
voltage V_Cn(s):
⎛
⎞
V_Cn(s)
=
⎜
⎜
⎜
⎝
-----------^R-----ⁿ---^t--^c---ⁿ----^e---^t-----------
R_ntcnet
+
-^R----^s---^u---^m---
N
×
D_-----NC-----R_{---⎟⎟⎟}
⎠
× I_o(s) × A_cs(s)
(EQ. 22)
R_ntcnet
=
-⁽--^R----ⁿ----^t--^c---^s----+-----^R----ⁿ----^t-^c----⁾---^×-----^R----^p--
R_ntcs + R_ntc + R_p
A_cs(s)
=
----¹----+------^ω-----^s----L-----
1
+
------^s------
ω_sns
(EQ. 23)
(EQ. 24)
27
FN8336.0
August 6, 2012