ISL6316 Datasheet, PDF (20/29 Pages) Intersil Corporation – Enhanced 4-Phase PWM Controller with 6-Bit VID Code Capable of Precision RDS(ON) or DCR Differential Current Sensing for VR10 Application

ISL6316
Overcurrent Protection
ISL6316 has two levels of overcurrent protection. Each phase
is protected from a sustained overcurrent condition on a
delayed basis, while the combined phase currents are
protected on an instantaneous basis.
In instantaneous protection mode, the ISL6316 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 100µA
reference current as shown in Figure 12. Once the average
current exceeds the reference current, a comparator triggers
the converter to shutdown.
In individual overcurrent protection mode, the ISL6316
continuously compares the current of each channel with the
same 100µA reference current. If any channel current
exceeds the reference current continuously for eight
consecutive cycles, the comparator triggers the converter to
shutdown.
OUTPUT CURRENT
0A
OUTPUT VOLTAGE
0V
2ms/DIV
FIGURE 13. OVERCURRENT BEHAVIOR IN HICCUP MODE.
F_SW = 500kHz
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 are open-drain outputs, and external
pull-up resistors are required.
VR_FAN signal indicates that the temperature of the voltage
regulator is high and more cooling airflow is needed. 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. VR_HOT signal may be tied to the
CPU’s PROCHOT signal.
The diagram of thermal monitoring function block is shown in
Figure 14. One NTC resistor should be placed close to the
power stage of the voltage regulator to sense the operational
temperature, and one pull-up resistor is needed to form the
voltage divider for TM pin. As the temperature of the power
stage increases, the resistance of the NTC will reduce,
resulting in the reduced voltage at TM pin. Figure 15 shows
the TM voltage over the temperature for a typical design with
a recommended 6.8kΩ NTC (P/N: NTHS0805N02N6801 from
Vishay) and 1kΩ resistor RTM1. We recommend using those
resistors for the accurate temperature compensation.
There are two comparators with hysteresis to compare the TM
pin voltage to the fixed thresholds for VR_FAN and VR_HOT
signals respectively. VR_FAN signal is set to high when TM
voltage is lower than 33% of Vcc voltage, and is pulled to
GND when TM voltage increases to above 39% of Vcc
voltage. VR_FAN is set to high when TM voltage goes below
28% of Vcc voltage, and is pulled to GND when TM voltage
goes back to above 33% of Vcc voltage. Figure 16 shows the
operation of those signals.
Based on the NTC temperature characteristics and the
desired threshold of VR_HOT signal, the pull-up resistor
RTM1 of TM pin is given by:
R_TM1 = 2.75xR_NTC(T3)
(EQ. 16)
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 13) 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.
R_NTC(T3) is the NTC resistance at the VR_HOT threshold
temperature T3.
20
FN9227.0
August 31, 2005