ISL6327 Datasheet, PDF (20/30 Pages) Intersil Corporation – Enhanced 6-Phase PWM Controller with 8-Bit VID Code and Differential Inductor DCR or Resistor Current Sensing

ISL6327
Undervoltage Detection
The undervoltage threshold is set at 50% of the VID voltage.
When the output voltage at VSEN is below the undervoltage
threshold, VR_RDY gets pulled low. When the output
voltage comes back to 60% of the VID voltage, VR_RDY will
return back to high.
Overvoltage Protection
Regardless of the VR being enabled or not, the ISL6327
overvoltage protection (OVP) circuit will be active after its
POR. The OVP thresholds are different under different
operation conditions. When VR is not enabled and before
the 2nd soft-start, the OVP threshold is 1.275V. Once the
controller detects a valid VID input, the OVP trip point will be
changed to the VID voltage plus 175mV.
Two actions are taken by the ISL6327 to protect the
microprocessor load when an overvoltage condition occurs.
At the inception of an overvoltage event, all PWM outputs
are commanded low instantly (less than 20ns). This causes
the Intersil drivers to turn on the lower MOSFETs and pull
the output voltage below a level to avoid damaging the load.
When the VDIFF voltage falls below the DAC plus 75mV,
PWM signals enter a high-impedance state. The Intersil
drivers respond to the high-impedance input by turning off
both upper and lower MOSFETs. If the overvoltage condition
reoccurs, the ISL6327 will again command the lower
MOSFETs to turn on. The ISL6327 will continue to protect
the load in this fashion as long as the overvoltage condition
occurs.
Once an overvoltage condition is detected, normal PWM
operation ceases until the ISL6327 is reset. Cycling the
voltage on EN_PWR, EN_VTT or VCC below the POR-
falling threshold will reset the controller. Cycling the VID
codes will not reset the controller.
Overcurrent Protection
ISL6327 has two levels of overcurrent protection. Each
phase is protected from a sustained overcurrent condition by
limiting its peak current, while the combined phase currents
are protected on an instantaneous basis.
In instantaneous protection mode, the ISL6327 utilizes the
sensed average current I_AVG to detect an overcurrent
condition. See the Channel-Current Balance section for
more detail on how the average current is measured. The
average current is continually compared with a constant
85µA reference current as shown in Figure 9. Once the
average current exceeds the reference current, a
comparator triggers the converter to shutdown.
At the beginning of overcurrent shutdown, the controller
places all PWM signals in a high-impedance state within
20ns commanding the Intersil MOSFET driver ICs to turn off
both upper and lower MOSFETs. The system remains in this
state a period of 4096 switching cycles. If the controller is still
enabled at the end of this wait period, it will attempt a soft-
start. If the fault remains, the trip-retry cycles will continue
indefinitely (as shown in Figure 10) until either controller is
disabled or the fault is cleared. Note that the energy
delivered during trip-retry cycling is much less than during
full-load operation, so there is no thermal hazard during this
kind of operation.
OUTPUT CURRENT
0A
OUTPUT VOLTAGE
0V
2ms/DIV
FIGURE 10. OVERCURRENT BEHAVIOR IN HICCUP MODE.
F_SW = 500kHz
For the individual channel overcurrent protection, the
ISL6327 continuously compares the sensed current signal of
each channel with the 120µA reference current. If one
channel current exceeds the reference current, ISL6327 will
pull PWM signal of this channel to low for the rest of the
switching cycle. This PWM signal can be turned on next
cycle if the sensed channel current is less than the 120µA
reference current. The peak current limit of individual
channel will not trigger the converter to shutdown.
The overcurrent protection level for the above two OCP
modes can be adjusted by changing the value of current
sensing resistors. In addition, ISL6327 can also adjust the
average OCP threshold level by adjusting the value of the
resistor from IOUT to GND. This provides additional safety
for the voltage regulator.
The following equation can be used to calculate the value of the
resistor R_IOUT based on the desired OCP level I_{AVG, OCP2}.
R_IOUT
=
---------------²----------------
I_{AVG, OCP2}
(EQ. 17)
Current Sense Output
The ISL6327 has 2 current sense output pins IDROOP and
IOUT; They are identical. In typical application, IDROOP pin
is connected to FB pin for the application where load line is
required. IOUT pin was designed for load current
measurement. As shown in typical application schematics
on pages 4 and 5, load current information can be obtained
by measuring the voltage at IOUT pin with a resistor
connecting IOUT pin to the ground. When the programmable
temperature compensation function of ISL6327 is properly
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FN9276.2
December 20, 2006