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DAC7731: DAC7731 / Supply sequence

S.Satoshi
Guru 21675 points
Part Number: DAC7731
Other Parts Discussed in Thread: TPS7A39

Hi,

I understand that the recommended supply sequence is VSS -> VCC -> VDD as comment below from DS. 

 The following supply sequence must be followed: VSS (device substrate) first, then VDD followed by VCC.

Now the customer plan to use TPS7A39 to generate +/- 12V for VSS and VCC, so VSS and VCC will power up simultaneously.

Then can you recommend to power up VSS and VCC simultaneously? Please let me know the concern if you can't recommend it.

Best Regards,

Satoshi / Japan Disty

  • 0
    TI__Genius 14220 points
    Hi Satoshi-san,

    Thank you for your query. The correct power supply sequence is VSS --> VDD --> VCC. Bringing up VCC before VDD is not recommended. You can use a power sequencer that can enable the power supplies in the given sequence. I am not sure whether it is possible with TPS7A39 or not - at least it doesn't look so looking at the datasheet. You can check with the power management forum for better information on this.

    Hope I have answered your question.

    Regards,
    Uttam Sahu
    Applications Engineer, Precision DACs
  • 0 in reply to Uttam Sahu
    Guru 21675 points
    Hi, Uttam,

    Thank you for your comment.
    If you recommend VSS --> VDD --> VCC sequence, then it means that "VDD followed by VCC" is typo, right?

    Next, I understand that the customer need to consider their power up sequence, but what do you have concern if they will not follow this sequence? Is there possible to damage device or can't get correct function after power up?

    Best Regards,
    Satoshi
  • 0 in reply to S.Satoshi
    TI__Genius 14220 points
    Hi Satoshi,

    I don't think it's a typo: "VDD followed by VCC" means first VDD and then VCC. However, I admit that these kind of requirements when expressed only textually, can be misinterpreted and hence, we will see if we can use more symbolic representation in future so that it is not ambiguous to users who don't have the first language as English (please do not consider this as a judgement on your English language skills).

    Regarding whether the device gets damaged or not, you should follow the below steps to ensure:
    1. There is no mention about the limit on VDD-VCC in the absolute max table - that means the device is not going to get damaged with incorrect power sequencing.
    2. However, the precision DACs usually load trimming codes during power up and the power sequencing usually takes care that it is completed properly. Sometimes, there are dependencies among different design blocks inside the IC. Hence, without the correct power sequencing many performance parameters cannot be guaranteed

    You can look at this training video for more details: training.ti.com/lessons-precision-dacs-power-sequencing

    Regards,
    Uttam