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UCD90120: Cascading using the GPI pin

Adrianna
Prodigy 100 points

Part Number: UCD90120
Other Parts Discussed in Thread: UCD90320, UCD90240, UCD9090A, UCD90160A,

I read this app note which says,

Another method to cascade multiple devices is to connect the power-good output of the first device to a MON/GPI pin of the second device; connect the power-good output of the second device to a MON/GPI pin of the third device, and so on.

and later on in the same paragraph,

Optionally, connect to the GPI pin instead of the MON pin if the UCD9090A, UCD90160A, UCD90240, and UCD90320 devices are used in the cascading method to save the MON pin for other uses.

However, does this mean that GPI can't be used at all for the power good input to the first sequencer if it were an older device such as the UCD90120 (which we're using due to supply chain issues)? Granted, it doesn't have the Fault Pin feature, but assuming we don't require that in our application I don't see why it can't just go to the GPI pin regardless. See image below for the configuration I'm referring to. I would very much like to free up that MON pin ;) 

 

Cheers, Adrianna

  • 0
    TI__Genius 10060 points

    Hi, Adrianna,

    If your application is not required, then feel free to use GPI instead of MON pin. However, since older UCD90XX devices (GEN 1), do not support GPI_FAULT_RESPONSE, nor FAULT_PIN, the de-assertion of GPI is not considered fault and cannot be used to shutdown rails. You will need to use LGPO pin connected to other devices' Control Pin to turn off these devices (section 2.1, page 11).

    Regards,

    Anne Ngo

    Texas Instruments

  • 0 in reply to Anne Ngo77
    Prodigy 100 points

    Thanks for your swift response. But it doesn't look like using the Control Pin lets you sequence the rails off in a specific order? That's what the section you sent implies. In that case, could I use the configuration below, with the MON pin, to perform both sequence on and off?

    In essence, all I want to do is sequence on and off using only UCD90120 devices. Our rails needs to come up and down in a specific order.

    Adrianna

  • 0 in reply to Adrianna
    TI__Genius 10060 points

    Hi, Adrianna,

    The Control Pin will turn the rails on and off based on LGPO assert/de-asserted (monitor Power Good). The order of rails that will be on/off can be set using Sequence-On and Sequence-Off dependencies, as well as TON_DELAY & TOFF_DELAY.

    Regards,

    Anne Ngo

    Texas Instruments

  • 0 in reply to Anne Ngo77
    Prodigy 100 points

    So... I can use the configuration in Fig 14 (of my previous post) with our older UCD device then? Since I can de-assert the Control Pin, but the interdependence between the sequencers (via their LGPOs) dictates that they have to come down in a specific order? 

  • +1 in reply to Adrianna
    TI__Guru 70370 points

    Hi

    The CONTROL pin is like a switch to power on or off the system. as for the order of how the system is power up or off it not controlled by the control pin. instead it is controlled by how you configure the dependencies among those rails. 

    please refer the attached guide.

    2450.UCD90xxx Quick Guide.pptx

    Regards

    Yihe