ISL6334A_14 Datasheet, PDF (23/31 Pages) Intersil Corporation – VR11.1, 4-Phase PWM Controller with Light Load Efficiency Enhancement and Load Current Monitoring Features

ISL6334, ISL6334A
For the individual channel overcurrent protection, ISL6334,
ISL6334A continuously compares the sensed current signal
of each channel with the 129µA reference current. If one
channel current exceeds the reference current, ISL6334,
ISL6334A 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
129µA 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.
The diagram of thermal monitoring function block is shown in
Figure 12. 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 the TM pin. As the temperature of the power
stage increases, the resistance of the NTC will reduce, resulting
in the reduced voltage at the TM pin. Figure 13 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. The VR_FAN signal is set to
high when the TM voltage is lower than 39.1% of VCC
voltage, and is pulled to GND when the TM voltage
increases to above 45.1% of VCC voltage. The VR_FAN
signal is set to high when the TM voltage goes below 33.3%
of VCC voltage, and is pulled to GND when the TM voltage
goes back to above 39.1% of VCC voltage. Figure 14 shows
the operation of those signals.
VCC
VR_FAN
R_TM1
TM
0.391V_CC
VR_HOT
o_c
R
NTC
0.333V_CC
FIGURE 12. BLOCK DIAGRAM OF THERMAL MONITORING
FUNCTION
100
90
80
70
60
50
40
30
20
0 20 40 60 80 100 120 140
TEMPERATURE (°C)
FIGURE 13. THE RATIO OF TM VOLTAGE TO NTC
TEMPERATURE WITH RECOMMENDED PARTS
TM
0.451*Vcc
0.391*Vcc
0.333*Vcc
VR_FAN
VR_HOT
TEMPERATURE
T1 T2 T3
FIGURE 14. VR_HOT AND VR_FAN SIGNAL vs TM VOLTAGE
Based on the NTC temperature characteristics and the
desired threshold of the VR_HOT signal, the pull-up resistor
RTM1 of TM pin is given by Equation 18:
R_TM1 = 2.75xR_NTC(T3)
(EQ. 18)
R_NTC(T3) is the NTC resistance at the VR_HOT threshold
temperature T3.
23
FN6482.2
February 1, 2013