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UCD9081: Product recommendation for sequencers that supplies down based on voltage only.

Kishen Someshwar
Intellectual 1625 points
Part Number: UCD9081
Other Parts Discussed in Thread: TPS3702, , UCD9090A

Hello Team,

I am trying to find a sequencer for a customer who in their application want to sequence down based on voltage only. I had previously suggested a Supervisor instead like the TPS3702, but the customer was wondering do we have a sequencer similar to this product. Below is what the customer is trying to achieve :

"  So I am trying to design power sequencing for an Arria 10 FPGA device. The FPGA could get damaged instantly if the wrong power down sequence occurs. Ideally, I would have a voltage supervisor monitoring the main input voltage. As soon as it detects a power loss, the FPGA will be put into a low power state and the power down sequence has to initiate. As shown below group 3 would be disabled as soon as a power loss is detected, group 2 would go down immediately after group 3 drops passed 10%, group 1 would immediately be disabled after group 2 dropped passed 10%. If group 3 takes too long to discharge and group 2 is discharged before it, the FPGA can get damaged.

 

I could add a long delay time and *assume the rails discharge, but then I have to have a huge bulk capacitance to hold the main rail up until sequencing is done properly. If the bulk capacitance is not large enough, the sequencer will lose power and not sequence the rails properly. That is why for me it would be ideal to sequence the supplies down based on voltage only.

 

I could as you describe setup fault slaves but how do I know when the rail that caused the fault actually reaches the 10% threshold?

 

The TPS3702 would actually be something I could probably use, but I am surprised that there are no digital sequencers that would provide similar functionality."

Would you'll know what could I suggest the customer to use in their application ?

Thank you for your time.

Sincerely,

Kishen

  • 0
    TI__Guru 58070 points
    HI Kishen
    UCD9090A is a good candaiate for this applicaiton. I do not think UCD9081 has that capability.
    In the UCD9090A, each rail can have its own sequencing off depenencies based on other rails
    the rail can not be off unless its depencencies(rails) are below POWER_GOOD_OFF threshold(programmable). The setting could be:
    1. set all three group as fault shutdown slave of VIN rail
    2. for rails on group 3, there is no sequencing off dependencies and their POWER_GOOD_OFF threshold will be 10% off norminal voltage.
    3 for rails on group 2, their sequenceing off depencencies will be group 3 and POWER_GOOD_OFF threshold of grop2 will be 10% off their norminal voltage.
    4. for rail on group 1, their sequencing off depenencies will be group 2.
    When the UCD detects VIN lost(via another MON pin), it will try to shutdown three group as fault shutdown slave. since group 3 has no depenencies, they will be off first. when GROUP3 falls 10%, GROUP2 will be off. when GROUP2 falls 10%, group1 will be off.

    This can ensure that FPGA was shutdown properly to avoid any damage.

    Regards
    Yihe
  • 0 in reply to yihe
    TI__Intellectual 1625 points
    HI Yihe,

    Thank you for the recommendation and explanation. The customer was satisfied with this choice. However if they drop the min Voltage below 3V to 2.9V would it be be able to do the sequencing properly? Since this device needs an external 3.3V supply for operation, they need to ensure they can power down the FPGA device properly if that 3.3V rail goes down.

    Thanks

    Kishen
  • 0 in reply to Kishen Someshwar
    TI__Guru 58070 points

    Kishen

    Device still function normal as long as VCC is above 2.9V(brownout threshold). So a external hold-up capacitor maybe required to let the UCD to properly power down the rails before 3.3V drop belows 2.9V.

    Thanks

    Yihe

  • 0 in reply to yihe
    TI__Intellectual 1625 points
    Got it. Thank you very much.

    Kishen