ISL6327IRZ-T Intersil, ISL6327IRZ-T Datasheet - Page 20

• Manufacturer Part Number: ISL6327IRZ-T
• Description: IC CTRLR PWM 6PHASE BUCK 48-QFN
• Manufacturer: Intersil

Specifications of ISL6327IRZ-T

• Pwm Type: Voltage Mode
• Number Of Outputs: 1
• Frequency - Max: 275kHz
• Duty Cycle: 25%
• Voltage - Supply: 4.75 V ~ 5.25 V
• Buck: Yes
• Boost: No
• Flyback: No
• Inverting: No
• Doubler: No
• Divider: No
• Cuk: No
• Isolated: No
• Operating Temperature: -40°C ~ 85°C
• Package / Case: 48-VQFN
• Frequency-max: 275kHz
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

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
condition. See “Channel-Current Balance” on page 12 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.
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.
AVG
20
to detect an overcurrent
ISL6327
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
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 the typical application
schematics on page 4 and page 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 used, the output current at IOUT pin is
proportional to the load current as shown in Figure 11.
R
FIGURE 10. OVERCURRENT BEHAVIOR IN HICCUP MODE.
FIGURE 11. VOLTAGE AT IOUT PIN WITH A NTC NETWORK
IOUT
0A
0V
=
0A
IOUT
-------------------------------
I
AVG OCP2
f
PLACED BETWEEN IOUT TO GROUND WHEN
LOAD CURRENT CHANGES
SW
based on the desired OCP level I
,
2
OUTPUT CURRENT
OUTPUT VOLTAGE
= 500kHz
V_IOUT, 200mV/DIV
2ms/DIV
50A
AVG, OCP2
100A
May 5, 2008
(EQ. 17)
FN9276.4
.