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TMDSCNCD28388D: TPS62420DRCR 3.3V and 1.2V Enable Pins

Euan T
Prodigy 40 points
Part Number: TMDSCNCD28388D

Tool/software:

Hello,

I currently powering my F28384DPTPS using the above TPS62420DRCR step down converter which was used in the reference design files of the TMDSCNCD28388D eval board. As the power sequencing requirements states that 3.3V must be powered prior to the 1.2V, R81 and C48 are used to ensure this on EN2. I would like to know if there is a risk of an undetermined state on Enable 2  and whether there is a requirement for a schmitt trigger on EN2.


 

Thanks!

  • 0
    TI__Mastermind 19840 points

    Hello Euan,

    thanks for reaching out in E2E.

    I think this design is OK and in normal case no risk for an undetermined sate of EN2. The only risk I can think of would be in case of fast power-off cycles at the 5V supply. If the power-off duration is shorter than the discharge time of capacitor C48 then the 1.2V would be enabled before the 3.3V converter. A Schmitt-trigger would not help here. Instead it would be required to ensure a slow shut down of the 5V supply (slower than the discharge of C48).

    Best regards,

    Andreas.

  • +1
    TI__Mastermind 19840 points

    Euan,

    another (maybe better) alternative would be to use the TPS62442 device, which has a PG pin (Power Good) for each output. Then you could use the PG1 signal to enable EN2. This method is used for the TMDSCNCD28P65X control card evaluation module reference design schematic.

    Best regards,

    Andreas.