isl62883c Intersil Corporation, isl62883c Datasheet - Page 17

• Manufacturer Part Number: isl62883c
• Description: Multiphase Pwm Regulator For Imvp-6.5? Mobile Cpus And Gpus
• Manufacturer: Intersil Corporation

FIGURE 12. DIFFERENTIAL SENSING AND LOAD LINE
As the load current increases from zero, the output
voltage will droop from the VID table value by an amount
proportional to the load current to achieve the load line.
The ISL62883C can sense the inductor current through
the intrinsic DC Resistance (DCR) of the inductors as
shown in Figure 1 on page 10 or through resistors in
series with the inductors as shown in Figure 2 on
page 11. In both methods, capacitor C
represents the inductor total currents. A droop amplifier
converts C
the gain set by resistor R
VID6 VID5 VID4 VID3 VID2 VID1 VID0
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
COMP
INTERNAL
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
n
TABLE 1. VID TABLE (Continued)
TO IC
IMPLEMENTATION
voltage into an internal current source with
E/A
0
0
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
FB
Σ
Idroop
VDAC
1
1
0
0
0
0
0
0
0
0
1
1
1
1
1
1
1
1
i
Rdroop
. The current source is used for
Vdroop
17
DAC
X 1
1
1
0
0
0
0
1
1
1
1
0
0
0
0
1
1
1
1
VIDs
RTN
VSS
RESISTOR
RESISTOR
“CATCH”
“CATCH”
1
1
0
0
1
1
0
0
1
1
0
0
1
1
0
0
1
1
n
voltage
VCC
VID<0:6>
VSS
VR LOCAL
SENSE
SENSE
0
1
0
1
0
1
0
1
0
1
0
1
0
1
0
1
0
1
VO
ISL62883C
0.1250
0.1125
0.1000
0.0875
0.0750
0.0625
0.0500
0.0375
0.0250
0.0125
0.0000
0.0000
0.0000
0.0000
0.0000
0.0000
0.0000
0.0000
(V)
V
O
load line implementation, current monitor and
overcurrent protection.
Figure 12 shows the load line implementation. The
ISL62883C drives a current source I
pin, described by Equation 1.
When using inductor DCR current sensing, a single NTC
element is used to compensate the positive temperature
coefficient of the copper winding thus sustaining the load
line accuracy with reduced cost.
I
voltage drop as shown in Equation 2.
V
line. Changing R
the load line slope. Since I
protection level, it is recommended to first scale I
based on OCP requirement, then select an appropriate
R
Differential Sensing
Figure 12 also shows the differential voltage sensing
scheme. VCC
voltage sensing signals from the processor die. A unity
gain differential amplifier senses the VSS
and add it to the DAC output. The error amplifier
regulates the inverting and the non-inverting input
voltages to be equal as shown in Equation 3:
Rewriting Equation 3 and substitution of Equation 2 gives
Equation 4 is the exact equation required for load line
implementation.
The VCC
processor die. The feedback will be open circuit in the
absence of the processor. As Figure 12 shows, it is
recommended to add a “catch” resistor to feed the VR
local output voltage back to the compensator, and add
another “catch” resistor to connect the VR local output
ground to the RTN pin. These resistors, typically
10Ω~100Ω, will provide voltage feedback if the system is
powered up without a processor installed.
I
VCC
VCC
V
droop
droop
droop
droop
droop
SENSE
SENSE
=
flows through resistor R
=
is the droop voltage required to implement load
value to obtain the desired load line slope.
2xV
----------------- -
SENSE
R
R
droop
+
–
i
Cn
VSS
V
SENSE
droop
and VSS
×
droop
SENSE
I
droop
=
and VSS
V
or scaling I
DAC
=
SENSE
V
droop
DAC
+
VSS
SENSE
droop
–
signals come from the
also sets the overcurrent
R
SENSE
droop
droop
are the remote
droop
and creates a
×
can both change
I
droop
SENSE
out of the FB
March 18, 2010
voltage
droop
FN7557.1
(EQ. 1)
(EQ. 2)
(EQ. 3)
(EQ. 4)