L6713ATR datasheet(54/64 Pages) STMICROELECTRONICS

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Thermal monitor

L6713A

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Thermal monitor

L6713A continuously senses the system temperature through TM pin: depending on the

voltage sensed by this pin, the device sets free the VR_FAN pin as a warning and, after

further temperature increase, also the VR_HOT pin as an alarm condition.

These signals can be used to give a boost to the system fan (VR_FAN) and improve the VR

cooling, or to initiate the CPU low power state (VR_HOT) in order to reduce the current

demand from the processor so reducing also the VR temperature. In a different manner,

VR_FAN can be used to initiate the CPU low power state so reducing the processor current

requirements and VR_HOT to reset the system in case of further dangerous temperature

increase.

Thermal sensors is external to the PWM control IC since the controller is normally not

located near the heat generating components: it is basically composed by a NTC resistor

and a proper biasing resistor RTM. NTC must be connected as close as possible at the

system hot-spot in order to be sure to control the hottest point of the VR.

Typical connection is reported in Figure 27 that also shows how the trip point can be easily

programmed by modifying the divider values in order to cross the VR_FAN and VR_HOT

thresholds at the desired temperatures.

Both VR_HOT and VR_FAN are active high and open drain outputs. Thermal Monitor

function is enabled if VCC>>UVLOVCC.

Figure 27.

System thermal monitor typical connections

Sense Element

(Place remotely, near Hot Spot)

+5V

TM Voltage - NTC=3300/4250K

2.00

2.20

2.40

2.60

2.80

3.00

3.20

3.40

3.60

3.80

4.00

100

105

110

115

120

Temperature [degC]

Rtm = 330

Rtm = 390

Rtm = 470

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