ISL6363 Datasheet, PDF (12/32 Pages) Intersil Corporation – Multiphase PWM Regulator for VR12™ Desktop CPUs

VW
Vcrm
COMP
Master
Clock
Clock1
PWM1
Clock2
PWM2
Clock3
PWM3
VW
ISL6363
Hysteretic
W in d o w
Vcrm
Master
Clock
Clock1
PWM1
Clock2
PWM2
Clock3
PWM3
VW
COMP
VW
Vcrs2 Vcrs3 Vcrs1
FIGURE 4. R3 MODULATOR OPERATION PRINCIPLES IN STEADY
STATE
Since the controller works with V_crs, which are large-amplitude
and noise-free synthesized signals, it achieves lower phase jitter
than conventional hysteretic mode and fixed PWM mode
controllers. Unlike conventional hysteretic mode converters, the
ISL6363 uses an error amplifier that allows the controller to
maintain a 0.5% output voltage accuracy.
Figure 5 shows the operation principles during load insertion
response. The COMP voltage rises during load insertion,
generating the master clock signal more quickly, so the PWM
pulses turn on earlier, increasing the effective switching frequency,
which allows for higher control loop bandwidth than conventional
fixed frequency PWM controllers. The VW voltage rises as the
COMP voltage rises, making the PWM pulses wider. During load
release response, the COMP voltage falls. It takes the master clock
circuit longer to generate the next master clock signal so the PWM
pulse is held off until needed. The VW voltage falls as the COMP
voltage falls, reducing the current PWM pulse width. This kind of
behavior gives the ISL6363 excellent response speed.
The fact that all the phases share the same VW window voltage
also ensures excellent dynamic current balance among phases.
Vcrs1
Vcrs3
Vcrs2
FIGURE 5. R3 MODULATOR OPERATION PRINCIPLES IN LOAD
INSERTION RESPONSE
Diode Emulation and Period Stretching of the ISL6363 can
operate in diode emulation (DE) mode to improve light load
efficiency. In DE mode, the low-side MOSFET conducts when the
current is flowing from source to drain and does not allow reverse
current, emulating a diode. As Figure 6 shows, when LGATE is on,
the low-side MOSFET carries current, creating negative voltage on
the phase node due to the voltage drop across the ON-resistance.
The ISL6363 monitors the current through monitoring the phase
node voltage. It turns off LGATE when the phase node voltage
reaches zero to prevent the inductor current from reversing the
direction and creating unnecessary power loss.
PHASE
UGATE
LGATE
IL
FIGURE 6. DIODE EMULATION
If the load current is light enough, as Figure 6 shows, the inductor
current will reach and stay at zero before the next phase node
pulse, and the regulator is in discontinuous conduction mode
(DCM). If the load current is heavy enough, the inductor current
will never reach 0A, and the regulator is in CCM although the
controller is in DE mode.
12
FN6898.0
September 29, 2011