ISL6363_14 Datasheet, PDF (13/32 Pages) Intersil Corporation – Multiphase PWM Regulator for VR12™ Desktop CPUs

ISL6363
Figure 7 shows the operation principle in diode emulation mode at
light load. The load gets incrementally lighter in the three cases
from top to bottom. The PWM on-time is determined by the VW
window size, therefore is the same, making the inductor current
triangle the same in the three cases. The ISL6363 clamps the
ripple capacitor voltage V_crs in DE mode to make it mimic the
inductor current. It takes the COMP voltage longer to hit V_crs,
naturally stretching the switching period. The inductor current
triangles move further apart from each other such that the
inductor current average value is equal to the load current. The
reduced switching frequency helps increase light load efficiency.
Vcrs
CCM/DCM BOUNDARY
VW
iL
Vcrs
VW ^{LIGHT DCM}
iL
Vcrs
DEEP DCM
VW
iL
FIGURE 7. PERIOD STRETCHING
Start-up Timing
With the controller's V_CC voltage above the POR threshold, the
start-up sequence begins when VR_ON exceeds the logic high
threshold. Figure 8 shows the typical start-up timing of VR1 and
VR2. The ISL6363 uses digital soft-start to ramp-up DAC to the
voltage programmed by the SetVID command. PGOOD is asserted
high and ALERT# is asserted low at the end of the ramp-up.
Similar results occur if VR_ON is tied to VCC, with the soft-start
sequence starting 800µs after VCC crosses the POR threshold.
VCC
VR_ON
DAC
PGOOD
ALERT#
SLEW RATE
2.5mV/µs
VID
3.8ms
VID COMMAND
VOLTAGE
…...
FIGURE 8. VR1 SOFT-START WAVEFORMS
Voltage Regulation and Load Line
Implementation
After the start sequence, the ISL6363 regulates the output voltage
to the value set by the VID information per Table 1. The ISL6363
will control the no-load output voltage to an accuracy of ±0.5%
over the range of 0.75V to 1.52V. A differential amplifier allows
voltage sensing for precise voltage regulation at the
microprocessor die.
TABLE 1. VID TABLE
VID
7 6 5 4 3 2 1 0 HEX
V_O (V)
0 0 0 0 0 0 0 0 0 0 0.00000
0 0 0 0 0 0 0 1 0 1 0.25000
0 0 0 0 0 0 1 0 0 2 0.25500
0 0 0 0 0 0 1 1 0 3 0.26000
0 0 0 0 0 1 0 0 0 4 0.26500
0 0 0 0 0 1 0 1 0 5 0.27000
0 0 0 0 0 1 1 0 0 6 0.27500
0 0 0 0 0 1 1 1 0 7 0.28000
0 0 0 0 1 0 0 0 0 8 0.28500
0 0 0 0 1 0 0 1 0 9 0.29000
0 0 0 0 1 0 1 0 0 A 0.29500
0 0 0 0 1 0 1 1 0 B 0.30000
0 0 0 0 1 1 0 0 0 C 0.30500
0 0 0 0 1 1 0 1 0 D 0.31000
0 0 0 0 1 1 1 0 0 E 0.31500
0 0 0 0 1 1 1 1 0 F 0.32000
0 0 0 1 0 0 0 0 1 0 0.32500
0 0 0 1 0 0 0 1 1 1 0.33000
0 0 0 1 0 0 1 0 1 2 0.33500
0 0 0 1 0 0 1 1 1 3 0.34000
0 0 0 1 0 1 0 0 1 4 0.34500
0 0 0 1 0 1 0 1 1 5 0.35000
0 0 0 1 0 1 1 0 1 6 0.35500
0 0 0 1 0 1 1 1 1 7 0.36000
0 0 0 1 1 0 0 0 1 8 0.36500
0 0 0 1 1 0 0 1 1 9 0.37000
0 0 0 1 1 0 1 0 1 A 0.37500
0 0 0 1 1 0 1 1 1 B 0.38000
0 0 0 1 1 1 0 0 1 C 0.38500
0 0 0 1 1 1 0 1 1 D 0.39000
0 0 0 1 1 1 1 0 1 E 0.39500
0 0 0 1 1 1 1 1 1 F 0.40000
0 0 1 0 0 0 0 0 2 0 0.40500
13
FN6898.1
September 5, 2013