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How do I power down slaved rails when a master rail drops below its PG limit?

Richard Yearsley
Prodigy 210 points

CPU_Board_Rev_E_V1.6_ip.xml

(Project attached)

Hi there,

I'm having difficulty getting rails to shut down when the master rail goes below its power-good limit. The PWR rail is the master rail which enables the 1V0, 1V2, 1V8, 1V5, 0V85 and 3V3 rails in sequence. This works perfectly, but now I want all of the rails to immediately switch off when the PWR rail drops below its PG limit (4.5V). I currently have PWR ticked in all of the slaved Seq Off Dependencies, but when I drop the PWR rail to ~4.25 the slaved rails stay on.

I've also previously tried using the under-volt fault on the PWR rail to shut-down all the slave rails, which works perfectly but I can't find any way to get get the device to re-sequence once the PWR rail goes back into its valid range (which could be seconds or hours later). Dropping the PWR rail to 0V and going back up to 5V will always work but a brown-out to less than 4.5V and then back up never re-sequences.

Ideally I'd like to get the 'Seq Off Dependencies' to switch off the slave rails and then go through the power-up sequence when PWR goes back into its valid PG range.

Many thanks,

Richard

  • 0
    TI__Genius 13700 points

    The Sequence Off Dependencies are used for a Managed power down in conjunction with the Control Pin or Operation Command to sequence off the rails.
    For unmanaged power down you were correct to use the Fault Slaves to disable all the rails when the master falls below the PG Off level.

    You correctly have the Master rail set to Re-Sequence but it will only attempt to re-sequence once, because the UV Fault requires the rail to reach regulation before it can declare another UV Fault and if it doesn't reach PG_ON level I believe there is a time out - (I haven't supported this product for a couple years but thought I'd jump in since you hadn't gotten a response yet).

    You can get around this by turning on the Time_On_Max Fault (under Fault Responses configuration section), this will declare another fault if the master rail fails to reach regulation after the defined MAX_TURN_ON time (under How to Turn Rail On/Off configuration section). This fault response can be set to re-sequence continually.

    You may want to add at least a small amount of time to the time between re-sequence attempts configuration.

  • 0 in reply to Brad
    Prodigy 210 points
    Thanks Brad, I'll give this a try.

    On another note, the 'email on reply' feature of this forum might be broken. In the past I've always had an email to say that somebody has responded, but not this time for some reason.

    Richard