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# THS3491: How to interpret TJ_Sense.

Part Number: THS3491

I'm looking for some guidance on how to interpret the TJ_SENSE specification for the THS3491. Since the test condition is to disable the part (Pd = 0V), the Ta is somewhat close to Tj, but what does the temperature value on parameter TJ_SENSE 25degC value actually mean? Also, if I look at the curves between MIN, TYP, MAX, at a specific voltage - say 1.1V, the temperature can vary almost 70 deg C, assuming the coefficient of 3.2mV/C. If this is really true, then how can I use the value to estimate the junction temperature? Figure 41 in the specification just seems to confuse me more. From my interpretation, I can't really use this voltage (TJ_SENSE) to estimate the junction temperature without a calibration of each part and probably on the TI EVM? I also tried plotting the curves with the knowledge that the test condition Ta varies from 22C to 32C, but it doesn't seem to help much. For now, I can assume the 1.06V is for a Tj of 25C and a coefficient of 3.2mV/C to calculate a junction temperature but will not rely on it.

• If you want to get more than a rough estimate, you indeed need calibration.

This is not a high-precision temperature sensor, but just a mechanism to allow protecting against overcurrent.

• Hi Bob,

the on chip temperature measurement is meant in combination with a two-point calibration performed by a microcontroller: Disable the OPAmp and measure the TJ_SENSE by the help of an ADC at two different ambient temperatures (oven). Then carry out a simple linear interpolation. This is no rocket science.

Kai

• hey Bob, this curve is just a characterization curve to extract the internal temp sense voltage without having to worry about internal die self heating. Actual operation is intended to warn equipment that the internal die temperature is getting extreme under actual operation. This feature was a request from National Instruments. There is also a output stage thermal shutdown feature I think around 160C and a current limit feature in the output stage. This device was intended for AWG output stages and protecting it from customer abuse was a big concern. Of course this curve continues up to that 160C thermal shutdown point.