FSCTxxA-UH5

7/6

Time

2

3

1

Fig. 8: Temperature evolution cases in mode OFF.

3. Internal temperature sensor

3.1 Temperature sensor linear response

FSCT devices feature an internal temperature sensor. This sensor results directly from silicon properties. It

is actually a voltage reference which is proportional to the absolute temperature, as it is an image of the Sili-

con thermal voltage "Vt" (refer to the following equation).

Vt

kT

q

= ⋅ with:

k Boltzmann cons

t

T absolute temperature K

q

:

tan

:(

)

.

=⋅

16 10

19

−











C

sensing method (-2mV/°C, sometimes used in thermal protections) because of its better accuracy (low im-

pact of process dispersions).

This signal is then processed to provide the desired OUT voltage range.

This internal sensor allows users not to use a Negative Temperature Coefficient thermistor (NTC).

Hence, users get rid of Joule effect, due to NTC bias current, that disturbs the temperature measurement.

Furthermore, the FSCT response is linear with the temperature. This simplifies the thermal study and the

heat sink rating for the power supply components or for the microprocessor.

NTC thermistors users need also to add a fixed resistor in order to get a linear thermal response from such

kind of sensor. The linear behavior is also only ensured for a restricted temperature range.

3.2 IPPAK mounting considerations

First, it should be noted that the tab is directly connected to the GND pin; then care must be taken when the

FSCT is glued to a heatsink. If this heatsink is at a differential voltage that the Ground, an electrical insula-

tor has to be added between the tab and the heat-sink.

Using non-isolated Through-Hole package like the IPPAK offers also a lot of benefits, compared to NTC

bulbs. Indeed, NTC do not offer a flat area like IPPAK package. Users need to add some glue to ensure

contact of the NTC bulb and the heat sink, at the cost of an increase in the thermal impedance and

response.