DAC7311: maximum output current of DAC7311

Hi Longchang,

Thank you for your query. The maximum output current of a DAC is not fixed and is decided by two parameters: short-circuit current and the maximum power dissipation. The short circuit current is the hard limit independent of any other parameters. However, the max power dissipation also sets a limit on how much current the DAC can source depending on the code, much below the short circuit current limit. The max power dissipation is subsequently dependent on the maximum junction temperature. The following steps show the calculation of the output current limit:

Max junction temperature Tj-max = 150 oC
Considering there is no heat-sink, The junction to ambient thermal resistance is Rth-ja = 216.4 oC/W (please note that this is the worst case without considering the heat-sinking properties of the PCB)

The following equation should be satisfied for proper operation:

Tj-max = Pd-max * Rth-ja + Ta-max, where Ta-max is the maximum ambient temperature for the application

Now Pd-max = Pdq-max + (Avdd - Vout)*Iout-max, where Pdq-max is the maximum quiescent power dissipation and is given in the datasheet for different supply voltages

Please note that Iout-max increases with Vout. It can be shown that for a resistive load, the maximum device power dissipation will occur at the mid-code.

Hope this answers your question.

Regards,
Uttam Sahu
Applications Engineer, Precision DACs