The DACx760 is designed for a maximum junction temperature of +150°C. In cases where the maximum AVDD is driving maximum current into ground, this could be exceeded. Use the following equation, from Section 7.1, to determine the maximum junction temperature that can be reached:
The power dissipation can be calculated by multiplying all the supply voltages with the currents supplied, which is found in the Power Requirements subsection of Section 7.5.
Consider an example: IOUT is enabled, supplying 24 mA into GND with a 25°C ambient temperature, AVDD of 24 V, AVSS is tied to GND and DVDD is generated internally. From the specifications table, the maximum value of AIDD = 3 mA when IOUT is enabled and DAC code = 0x0000. Also, the maximum value of DIDD = 1 mA. Accordingly, the worst case power dissipation is 24 V × (24 mA + 3 mA + 1 mA) = 672 mW. Using the RθJA value for the TSSOP package, we get TJmax = 25°C + (32.3 × 0.672)°C = 46.7°C. At 85°C ambient temperature, the corresponding value of TJmax is 106.7°C. Using this type of analysis, the system designer can both specify and design for the equipment operating conditions. Note that the thermal pad in both packages is recommended to be connected to a copper plane for enhanced thermal performance.