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DAC8775EVM: EVM startup questions

Jose Maroto
Expert 3510 points
Part Number: DAC8775EVM
Other Parts Discussed in Thread: DAC8771

Dear team,

I got some question from customers I summarize here:

1.) Can I power the EVM with 15V without problems? It seems so but please confirm.

2.) They want to use the EVM for  +/-20mA application, should they set  the current limit to +/ -24mA or to +/ -20mA?

3.) Regarding the buck-boost, which is the suitable mode to use in order to get +/-20mA?

3.a) Would positive and negative enable be the best choice?

3.b) Could the full tracking feature make the chip hotter?

3.c) Would the clamps be limited by the maximum resistance of the loop?

Could you please help?

Thanks and regards, Jose

  • 0
    TI__Genius 11750 points

    Hi Jose,

    Thanks for the post.  As you have noticed, (1) the DAC8771 device accepts a wide range of input supply values, 12V to 36V, making the 15V supply mentioned an acceptable candidate.  The current loop requirements is typically based on customer interest and the desired application. (2) If they choose to report on a 4 to 20mA structure, then this current range should suffice, however, a 0 to 24mA range is additionally included in the case that the device needs to provide some form or loop-error reporting through the loop current value. (3) Both the negative and positive arm of the buck and boost should be enabled for bipolar operation.  The adaptive power (full-tracking feature) was implemented to decrease power dissipation, reducing heat. Page 8 of the datasheet displays the necessary compliance voltage of the +-24mA output range.  The max compliance voltage is (VPOS_IN_X - 3V), while the min is (|VNEG_IN_X|+3).  VPOS_IN_X/VNEG_IN_X has a max and min value of 32V and -18V, respectively.  You can use the desired output current and multiply this value by the restive load to verify that it meets IOUT voltage compliance.

    Best Regards,

    Matt