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UCD9081: In Advanced mode (with Allowed Self-Dependencies), the power sequencer doesn't cycle output EN signals, when a fault is present on input MON signals

Nick
Prodigy 15 points
Part Number: UCD9081

Signal connections on UCD9081 8-ch Power sequencer:
For simplicity, I am presenting only 4 signals where there is a problem.

There are four power good signals on input monitoring pins and 4 output enable signals.
They are connected on UCD9081 in this order:

Inputs - rail # - Outputs - parent rail
==============================
MON4 - rail 4 - EN4      (parent rail is 4)
MON5 - rail 5 - EN5      (parent rail is 5)
MON6 - rail 6 - EN6      (parent rail is 6)
MON7 - rail 7 - EN7      (parent rail is 7)

MON4, 5, 6, and 7 are power good signals coming from 4 power rails.
EN# signals are delayed 10ms after the MON# signals.

Setup:
1) UCD9081 EVM GUI  is set: Advanced Mode, Allow Self-dependencies.
2) Alarm Processing:  Sequence
3) Parent rails setup:
Output EN# is referenced to the same input rail MON#.

EN4 (parent rail is 4)
EN5 (parent rail is 5)
EN6 (parent rail is 6)
EN7 (parent rail is 7)

Problem:
When the fault is simulated on any of MON4, 5, 6, or 7 inputs, the power sequencer doesn't sequence output signals EN4, 5, 6, and 7.

Note:
If Advanced Mode with Self Dependences is NOT used, then EN 4, 5, 6, and 7 are sequenced when a fault is present on MON 4, 5, 6, or 7 inputs.
But the problem, in this case, is that dependencies are now different and not desirable, and timing gets different:

Now dependencies are like this:

EN4 (parent rail is 3)
EN5 (parent rail is 4)
EN6 (parent rail is 5)
EN7 (parent rail is 6)

Why power sequencer in this application is not sequencing EN4, 5, 6, and 7 signals (toggling OFF-ON) after a fault is present on input MON signals when Advanced mode is used with  Allowed Self-dependencies?

Thank you,

  • 0
    TI__Guru 60280 points

    Hi

    Please share your configuration files so that we can better help review.

    Regards

    Yihe

  • 0 in reply to yihe
    Prodigy 15 points

    Hi,
    Due to project confidentiality, we need to switch to email.
    Please send me an email.
    I will send you more details with a configuration file.

    Thank you,
    ========

  • 0 in reply to Nick
    TI__Guru 60280 points

    HI

    Please request friendship so that you can share the file offline.

    Regards

    Yihe

  • 0 in reply to yihe
    TI__Guru 60280 points

    HI

    The option of "Allow Self-dependencies" is dummies and it does not change any behaviors of the devices. it is just a flag without real action

    I am surprised that you observed different behaviors 

    Based on your setting, the following is the right order to turn on EN4 and EN7. they shall also re-sequence based on the order. 

    EN4 (parent rail is 3)
    EN5 (parent rail is 4)
    EN6 (parent rail is 5)
    EN7 (parent rail is 6)

     

    Regards

    Yihe

  • 0 in reply to yihe
    TI__Guru 60280 points

    Hi

    I saw your reply on the private message. If you make the rail as its onw dependencies. after the fault, you have to make sure the MON signal is back to normal. For example, if you make a UV fault on the rail 4 and rail 4 is self-dependency, did you recover the rail 4 from UV fault? was the voltage on the rail4?

    Regards

    Yihe

  • 0 in reply to yihe
    Prodigy 15 points

    Power good signals on MON inputs and enable output signals EN are connected in such a way that we would need Self dependencies enabled to get correct dependencies and timing.


    EN4 (parent rail is 4)
    EN5 (parent rail is 5)
    EN6 (parent rail is 6)
    EN7 (parent rail is 7)

    When testing the Advanced option with Self-dependencies, the timing is correct, but there is a problem that the UCD9081 power sequencer doesn't re-sequence when a fault is present on MON inputs.

    Each of the monitor inputs MON 4, 5, 6, (these are power good signals), are connected to the middle point of a separate resistor divider.

    Faults on MON inputs are simulated by manual bridging the bottom resistor in the resistor divider to the GND.

    When a fault is simulated, EN outputs are turned OFF, therefore power rails are disabled.

    When a fault is removed, EN signals stay OFF and rails are not turned ON.

  • 0 in reply to Nick
    TI__Guru 60280 points

    Hi

    I tested on the UCD9081 EVM and was not able to see the issue of resequencing. 

    My test is very simple, I let the rail4 to be the only self-dependency rail.

    Rail 1-3 are dependent on time only 

    Rail5->Rail6->Rail7->Rail 8

    When Power up the EVM, rail 1-3 are ON as expected, but rail 4-8 are not the reason is that MON 4's input was not ready, I applied a external voltage to the MON4 pin, rail 4-8 are on based on the sequencing . 

    On the next, i short the MON4 to GND to generate the UV fault.

    as soon as  I release the short, rail 4-8 are on as soon as the external voltage is applied on the MON4 pin again.

    UCD9081 - GUI config - with Self Depedencies - May 2nd TI.par

    So please double check that when the fault is removed, the voltage on the PIN is back to normal.

    Regards

    Yihe

  • 0 in reply to yihe
    Prodigy 15 points

    I found a mistake in my previous message.

    Here is behavior during fault.

    ***  Faults on MON inputs are simulated by manual bridging the bottom resistor in the resistor divider to the GND.

    When a fault is simulated, EN outputs are turned OFF, therefore power rails are disabled.

    When a fault is removed, EN signals stay OFF and rails are not turned ON.    ***

    I will try another test.

    Thanks,

  • 0 in reply to Nick
    TI__Guru 60280 points

    Hi

    I can see where the problem is.

    After the fault is removed, the EN will stay low until the corresponding MON has a correct voltage since it is self-dependency. 

    I am curious why a self-dependency is required n your system. 

    Regards

    Yihe