ISL6306 Datasheet, PDF (24/33 Pages) Intersil Corporation – 4-Phase PWM Controller with 8-Bit DAC Code Capable of Precision rDS ON or DCR Differential Current Sensing

ISL6306
Overcurrent Protection
ISL6306 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 ISL6306 utilizes the
sensed average current I_AVG to detect an overcurrent
condition. See “Channel-Current Balance” on page 15 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 ISL6306
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
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 PROC_HOT 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.
0V
2ms/DIV
FIGURE 13. OVERCURRENT BEHAVIOR IN HICCUP MODE.
VCC
F_SW = 500kHz
VR_FAN
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
TM1
TM
0.33V_CC
VR_HOT
o_c
R
NTC
0.28V_CC
FIGURE 14. BLOCK DIAGRAM OF THERMAL MONITORING
FUNCTION
24
FN9226.1
May 5, 2008