ISL6334DIRZ datasheet(20/28 Pages) INTERSIL

20 / 28 page

FN6802.2

August 31, 2010

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, ISL6334D

continuously compares the sensed current signal of each

channel with the 129µA reference current. If one channel

current exceeds the reference current, ISL6334D 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 6.8k

Ω NTC (P/N:

NTHS0805N02N6801 from Vishay) and 1k

Ω 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.

2ms/DIV

OUTPUT CURRENT

FIGURE 11. OVERCURRENT BEHAVIOR IN HICCUP MODE.

FSW = 500kHz

OUTPUT VOLTAGE

FIGURE 12. BLOCK DIAGRAM OF THERMAL MONITORING

FUNCTION

0.333VCC

0.391VCC

° C

TM1

NTC

VCC

VR_FAN

VR_HOT

FIGURE 13. THE RATIO OF TM VOLTAGE TO NTC

TEMPERATURE WITH RECOMMENDED PARTS

100

120

140

TEMPERATURE (°C)

ISL6334D

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