ISL78211 Datasheet, PDF (12/35 Pages) Intersil Corporation – Automotive Single-Phase Core Regulator for IMVP-6™ CPUs

ISL78211
Theory of Operation
The ISL78211 is a single-phase regulator implementing
Intel^™ IMVP-6^™ protocol and includes an integrated gate
driver for reduced system cost and board area. The
ISL78211 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 ISL78211 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 ISL78211 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 ISL78211 to achieve lower
output ripple and lower phase jitter than either
conventional hysteretic or fixed frequency PWM
controllers. Unlike conventional hysteretic converters,
the ISL78211 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 start-up, 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 20mV of the boot
voltage the ISL78211 will count 13 clock cycles, then pull
CLK_EN# low, and charge/discharge the SOFT cap with
approximately 200µA, therefore VO slews at 10mV/µs to
the voltage set by the VID pins. In approximately 7ms,
PGOOD is asserted HIGH. Figure 4 shows typical start-up
timing.
Static Operation
After the start-up 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 ISL78211 regulates the output voltage with ±0.5%
accuracy over the range of 0.7V to 1.5V.
VDD
VR_ON
100µs
20mV
10mV/µs
V_BOOT
SOFT AND VO
13xTs
2mV/µs
CLK_EN#
IMVP-VI PGOOD
~7ms
FIGURE 4. SOFT-START WAVEFORMS USING A 20nF
SOFT CAPACITOR
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 ISL78211 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.
The PMON pin is the power monitor output. The voltage
potential on this pin (V_PMON) is given by
V_PMON = 35x(V_SEN-V_RTN)x(V_DROOP-V_O). Since
V_SEN-V_RTN is the CPU voltage and V_DROOP-V_O represents
the inductor current, V_PMON is an analog voltage
indicating the power consumed by the CPU. V_PMON has
high bandwidth so it represents the instantaneous power
including the pulsation caused inductor current switching
ripple. The maximum available V_PMON is
approximately 3V.
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 ISL78211 controller is set
by the resistor R_FSET between pins VW and COMP, as
shown in Figures 2 and 3.
12
FN7578.0
March 8, 2010