ISL6326B Datasheet, PDF (21/30 Pages) Intersil Corporation – 4-Phase PWM Controller with 8-Bit DAC Code Capable of Precision DCR Differential Current Sensing

ISL6326B
MOSFETs to turn on. The ISL6326B 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 ISL6326B 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.
VR_RDY
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.
UV
50%
DAC
VDIFF
SOFT-START, FAULT
AND CONTROL LOGIC
-
OC
+
85µA
I_AVG
+
OV
-
-
OC
+
2.0V
IOUT
VID + 0.175V
FIGURE 9. VR_RDY AND PROTECTION CIRCUITRY
Overcurrent Protection
ISL6326B 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, ISL6326B 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.
The current out of IOUT pin is equal to the sensed average
current I_AVG. With a resistor from IOUT to GND, the voltage
at IOUT will be proportional to the sensed average current
and the resistor value. ISL6326B continuously monitors the
voltage at IOUT pin. If the voltage at IOUT pin is higher than
2V, a comparator triggers the overcurrent shutdown. By
increasing the resistor between IOUT and GND, the
overcurrent protection threshold can be adjusted to be less
than 100µA. For example, the overcurrent threshold for the
sensed average current I_AVG can be set to 80µA by using a
25kΩ resistor from IOUT to GND.
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
ISL6326B continuously compares the sensed current signal
of each channel with the 120µA reference current. If one
channel current exceeds the reference current, ISL6326B
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.
Thermal Monitoring (VR_HOT/VR_FAN)
There are two thermal signals to indicate the temperature
status of the voltage regulator: VR_HOT and VR_FAN. Both
VR_FAN and VR_HOT pins are open-drain outputs, and
external pull-up resistors are required. Those signals are
valid only after the controller is enabled.
The VR_FAN signal indicates that the temperature of the
voltage regulator is high and more cooling airflow is needed.
The VR_HOT signal can be used to inform the system that
the temperature of the voltage regulator is too high and the
CPU should reduce its power consumption. The VR_HOT
signal may be tied to the CPU’s PROC_HOT signal.
21
FN9286.0
April 21, 2006