ISL6353 Datasheet, PDF (18/30 Pages) Intersil Corporation – Multiphase PWM Regulator for VR12 DDR Memory Systems

ISL6353
TABLE 2. VID TABLE (Continued)
OFS7 OFS6 OFS5 OFS4 OFS3 OFS2 OFS1 OFS0 Hex
V_OFS
(V)
0 1 0 1 1 1 1 1 5 F 0.475
0 1 1 0 0 0 0 0 6 0 0.480
0 1 1 0 0 0 0 1 6 1 0.485
0 1 1 0 0 0 1 0 6 2 0.490
0 1 1 0 0 0 1 1 6 3 0.495
0 1 1 0 0 1 0 0 6 4 0.500
0 1 1 0 0 1 0 1 6 5 0.505
0 1 1 0 0 1 1 0 6 6 0.510
0 1 1 0 0 1 1 1 6 7 0.515
0 1 1 0 1 0 0 0 6 8 0.520
0 1 1 0 1 0 0 1 6 9 0.525
0 1 1 0 1 0 1 0 6 A 0.530
0 1 1 0 1 0 1 1 6 B 0.535
0 1 1 0 1 1 0 0 6 C 0.540
0 1 1 0 1 1 0 1 6 D 0.545
0 1 1 0 1 1 1 0 6 E 0.550
0 1 1 0 1 1 1 1 6 F 0.555
0 1 1 1 0 0 0 0 7 0 0.560
0 1 1 1 0 0 0 1 7 1 0.565
0 1 1 1 0 0 1 0 7 2 0.570
0 1 1 1 0 0 1 1 7 3 0.575
0 1 1 1 0 1 0 0 7 4 0.580
0 1 1 1 0 1 0 1 7 5 0.585
0 1 1 1 0 1 1 0 7 6 0.590
0 1 1 1 0 1 1 1 7 7 0.595
0 1 1 1 1 0 0 0 7 8 0.600
0 1 1 1 1 0 0 1 7 9 0.605
0 1 1 1 1 0 1 0 7 A 0.610
0 1 1 1 1 0 1 1 7 B 0.615
0 1 1 1 1 1 0 0 7 C 0.620
0 1 1 1 1 1 0 1 7 D 0.625
0 1 1 1 1 1 1 0 7 E 0.630
0 1 1 1 1 1 1 1 7 F 0.635
FB
E/A
COMP
Σ
DAC
VDAC
INTERNAL TO IC
X1
VCCSENSE
VR LOCAL
VO
“CATCH”
RESISTOR
RTN
VSS
VSSSENSE
“CATCH”
RESISTOR
FIGURE 9. DIFFERENTIAL SENSING
Figure 9 shows the differential voltage sensing scheme. VCC_SENSE
and VSS_SENSE are the remote voltage sensing signals from the DDR
memory. A unity gain differential amplifier senses the VSS_SENSE
voltage and adds it to the DAC output. The error amplifier regulates
the inverting and the non-inverting input voltages to be equal as
shown in Equation 1:
VCC_SENSE = V_DAC + VSS_SENSE
(EQ. 1)
Rewriting Equation 1 gives Equation 2:
VCC_SENSE – VSS_SENSE = V_DAC
(EQ. 2)
The VCC_SENSE and VSS_SENSE signals are routed from the
memory socket. In most cases the remote sensing location will
be on the PCB right next to one of the DDR memory sockets. If a
remote sensing location is used on a module that passes through
a socket then the feedback signals will be open circuit in the
absence of the module. As shown in Figure 9, a “catch” resistor
should be added in this case to feed the local VR output voltage
back to the compensator, and another “catch” resistor should be
added to connect the local VR output ground to the RTN pin.
These resistors, typically 10Ω~100Ω, will provide voltage
feedback if the system is powered up without any memory cards
installed.
Inductor DCR Current-Sensing Network
The ISL6353 can sense the inductor current through the intrinsic DC
Resistance (DCR) of the inductors or through precision resistors in
series with the inductors. With both current-sensing methods, the
voltage across capacitor C_n represents the total inductor current
from all phases. An amplifier converts the C_n voltage, V_Cn, into an
internal current source, I_sense, with the gain set by resistor R_i shown
in Equation 3.
I_sense
=
V_----C---n--
R_i
(EQ. 3)
18
September 15, 2011
FN6897.0