ISL6263 Datasheet, PDF (11/19 Pages) Intersil Corporation – 5-Bit VID Single-Phase Voltage Regulator for IMVP-6+ Santa Rosa GPU Core

ISL6263
DROOP pin minus the output voltage measured at the VO
pin, is proportional to the total inductor current. This
information is used exclusively to achieve the IMVP-6+ load
line as well as the overcurrent protection. It is important to
note that this current measurement should not be confused
with the synthetic current ripple information created within
the R³ modulator.
When using inductor DCR current sensing, an NTC element
is used to compensate the positive temperature coefficient of
the copper winding thus maintaining the load-line accuracy.
Processor Socket Kelvin Voltage Sensing
The remote voltage sense input pins VSEN and RTN of the
ISL6263 are to be terminated at the die of the GPU through
connections that mate at the processor socket. (The signal
names are Vcc_sense and Vss_sense respectively.) Kelvin
sensing allows the voltage regulator to tightly control the
processor voltage at the die, compensating for various
resistive voltage drops in the power delivery path.
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 ISL6263 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 Ropn1 and
Ropn2 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.
+
Σ
+
VDIFF
VDD
−
OCP
+
+
−
10µA _↓
OCSET
+
DROOP
−
VSUM
DFB
DROOP
VO
VSEN
+
RTN
−
R_OCSET
PHASE
R_S
C_FILTER1
R_FILTER1
R_FILTER2
C_FILTER2
C_FILTER3
L_OUT
DCR
C_OUT
ESR
V_{CC_SNS}
V_{SS_SNS}
To
Processor
Socket
Kelvin
Connections
FIGURE 5. SIMPLIFIED VOLTAGE DROOP CIRCUIT WITH GPU SOCKET KELVIN SENSING AND INDUCTOR DCR CURRENT SENSING
High Efficiency Diode Emulation Mode
The ISL6263 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. Depending upon the VID and FDE pin states, an
improvement in light-load efficiency can be achieved by
operating in discontinuous-conduction-mode (DCM) where
the low-side MOSFET is operated in diode-emulation-mode
(DEM), forcing the low-side MOSFET 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 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 in CCM when the output load current
is less than ½ the inductor ripple current. Sinking negative
inductor through the low-side MOSFET lowers efficiency
through unnecessary conduction losses. Upon entering
DEM the PWM switching frequency is automatically shifted
downward by an increase of the window voltage V_W of 33%.
The PWM switching frequency will continue to decrease as
the load continues to decrease. The reduction of PWM
11
FN9213.2
June 10, 2010