ISL6263D Datasheet, PDF (10/17 Pages) Intersil Corporation – Pre-biased Output Start-Up Capability

ISL6263D
VID CODE
VID2
VID1
VID0
0
0
0
0
0
1
0
1
0
0
1
1
1
0
0
1
0
1
1
1
0
1
1
1
TABLE 1. VID AND OFFSET TRUTH TABLE
DAC OUTPUT VOLTAGE (V_SOFT) (mV)
OFFSET1 = 0
OFFSET1 = 1
OFFSET0 = 0
OFFSET0 = 1
OFFSET0 = 0
OFFSET0 = 1
1050
1062.5
1075
1087.5
1000
1012.5
1025
1037.5
950
962.5
975
987.5
900
912.5
925
937.5
850
862.5
875
887.5
800
812.5
825
837.5
750
762.5
775
787.5
700
712.5
725
737.5
Since the voltage feedback is sensed at the processor die,
removing the GPU will open the voltage feedback path of the
regulator, causing the output voltage to rise towards VIN.
The ISL6263D will shut down when the voltage between the
VO and VSS pins exceeds the severe overvoltage protection
threshold V_OVPS of 1.55V. To prevent this issue from
occurring, it is recommended to install resistors R_OPN1 and
R_OPN2, as shown in Figure 5. These resistors provide
voltage feedback from the regulator local output in the
absence of the GPU. These resistors should be in the range
of 20Ω to 100Ω
Diode Emulation Mode and Audio Filter Operation
The ISL6263D operates in continuous-conduction-mode
(CCM) during heavy load for minimum conduction loss by
forcing the low-side MOSFET to operate as a synchronous
rectifier. An improvement in light-load efficiency is achieved
VDD
-
OCP
+
+
-
10µA _
OCSET
+
ISP
Isense
-
ISN
ICOMP
VO
R_OCSET
by allowing the converter to operate in diode-emulation
mode (DEM) where the low-side MOSFET behaves as a
smart-diode, forcing the device to block negative inductor
current flow.
Positive-going inductor current flows from either the source of
the high-side MOSFET, or the drain of the low-side MOSFET.
Negative-going inductor current flows into the source of the
high-side MOSFET, or into the drain of the low-side MOSFET.
When the low-side MOSFET conducts positive inductor
current, the phase voltage will be negative with respect to the
VSS pin. Conversely, when the low-side MOSFET conducts
negative inductor current, the phase voltage will be positive
with respect to the VSS pin. Negative inductor current occurs
when the output DC load current is less than ½ the inductor
ripple current. Sinking negative inductor current through the
low-side MOSFET lowers efficiency through unnecessary
PHASE
R_S
L_OUT
DCR
C_OUT
ESR
+
-
VDIFF
VSEN
RTN
C_FILTER1
R_FILTER1
R_FILTER2
C_FILTER2
C_FILTER3
V_OUT
V_GND
TO
PROCESSOR
KELVIN
CONNECTIONS
FIGURE 5. SIMPLIFIED GPU VOLTAGE KELVIN SENSE AND INDUCTOR DCR CURRENT SENSE
10
FN6753.1
July 8, 2010