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AD7891: Thermal impedance

   Is it normal  working condition of the analog-to-digital converter
AD7891AS-1, when it's surface temperature is +40C and outter temperature is
about +20C?


Power dissipation of the AD7891 is about 100uW. Thermal resistance (thetaJA) of
the AS package is 95degC/W. Temperature difference between ambient and chip
temperature is 0.1 x 95 = 9.5degC. You are seeing a temperature rise of 20degC,
this could be because the heat dissipation capability of your board is
particularly poor (most heat escapes through the lead frame, so thick
connections to the power supply pins and a large ground area will improve the
heat dissipation.

A 20degC temp rise is not a problem in it self. Check the part is operatind
correctly and if possible measure the current consumption of the AD7891