ISL6261 Datasheet, PDF (11/34 Pages) Intersil Corporation – Single-Phase Core Regulator for IMVP-6 Mobile CPUs

ISL6261
Theory of Operation
The ISL6261 is a single-phase regulator implementing Intel^®
IMVP-6^® protocol and includes an integrated gate driver for
reduced system cost and board area. The ISL6261 IMVP-6^®
solution provides optimum steady state and transient
performance for microprocessor core voltage regulation
applications up to 25A. Implementation of diode emulation
mode (DEM) operation further enhances system efficiency.
The heart of the ISL6261 is the patented R³ Technology™,
Intersil’s Robust Ripple Regulator modulator. The R³â„¢
modulator combines the best features of fixed frequency and
hysteretic PWM controllers while eliminating many of their
shortcomings. The ISL6261 modulator internally synthesizes
an analog of the inductor ripple current and uses hysteretic
comparators on those signals to establish PWM pulses.
Operating on the large-amplitude and noise-free synthesized
signals allows the ISL6261 to achieve lower output ripple
and lower phase jitter than either conventional hysteretic or
fixed frequency PWM controllers. Unlike conventional
hysteretic converters, the ISL6261 has an error amplifier that
allows the controller to maintain 0.5% voltage regulation
accuracy throughout the VID range from 0.75V to 1.5V.
The hysteretic window voltage is with respect to the error
amplifier output. Therefore the load current transient results
in increased switching frequency, which gives the R³â„¢
regulator a faster response than conventional fixed
frequency PWM regulators.
Start-up Timing
With the controller’s VDD pin voltage above the POR
threshold, the start-up sequence begins when VR_ON
exceeds the 3.3V logic HIGH threshold. In approximately
100μs, SOFT and VO start ramping to the boot voltage of
1.2V. At startup, the regulator always operates in continuous
current mode (CCM), regardless of the control signals.
During this interval, the SOFT cap is charged by a 41μA
current source. If the SOFT capacitor is 20nF, the SOFT
ramp will be 2mV/μs for a soft-start time of 600μs. Once VO
is within 10% of the boot voltage and PGD_IN is HIGH for six
PWM cycles (20µs for 300kHz switching frequency),
CLK_EN# is pulled LOW, and the SOFT cap is
charged/discharged by approximate 200µA and VO slews at
10mV/μs to the voltage set by the VID pins. In approximately
7ms, PGOOD is asserted HIGH. Figure 4 shows typical
startup timing.
PGD_IN Latch
It should be noted that PGD_IN going low will cause the
converter to latch off. Toggling PGD_IN won’t clear the latch.
Toggling VR_ON will clear it. This feature allows the
converter to respond to other system voltage outages
immediately.
VDD
VR_ON
100us
SOFT &VO
PGD_IN
10mV/us
2mV/us ^Vboot
~20us
CLK_EN#
IMVP-VI PGOOD
~7ms
FIGURE 4. SOFT-START WAVEFORMS USING A 20nF SOFT
CAPACITOR
Static Operation
After the startup sequence, the output voltage will be
regulated to the value set by the VID inputs per Table 1,
which is presented in the lntel^® IMVP-6^® specification. The
ISL6261 regulates the output voltage with ±0.5% accuracy
over the range of 0.7V to 1.5V.
A true differential amplifier remotely senses the core voltage
to precisely control the voltage at the microprocessor die.
VSEN and RTN pins are the inputs to the differential
amplifier.
As the load current increases from zero, the output voltage
droops from the VID value proportionally to achieve the
IMVP-6^® load line. The ISL6261 can sense the inductor
current through the intrinsic series resistance of the
inductors, as shown in Figure 2, or through a precise resistor
in series with the inductor, as shown in Figure 3. The
inductor current information is fed to the VSUM pin, which is
the non-inverting input to the droop amplifier. The DROOP
pin is the output of the droop amplifier, and DROOP-VO
voltage is a high-bandwidth analog representation of the
inductor current. This voltage is used as an input to a
differential amplifier to achieve the IMVP-6^® load line, and
also as the input to the overcurrent protection circuit.
When using inductor DCR current sensing, an NTC
thermistor is used to compensate the positive temperature
coefficient of the copper winding resistance to maintain the
load-line accuracy.
The switching frequency of the ISL6261 controller is set by
the resistor R_FSET between pins VW and COMP, as shown in
Figures 2 and 3.
11
FN9251.1
September 27, 2006