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TPS65251 causing issues with Sitara processor

Edward Cocciadiferro
Prodigy 20 points
Other Parts Discussed in Thread: TPS65251

We are using the TPS65251 to generate 1.1v, 1.8v and 3.3v for a Sitara processor along with external memory (MT47H64M16NF-25E:M) and a few peripheral chips. Input to the TPS65251 is +15 VDC, from an external power supply.

 

We do sequence the power up on the TPS65251, via the Enable pins:

EN1, 1.1 VDC, 0.022uf

EN2, 1.8 VDC, no cap

EN3, 3.3 VDC, 0.01uF

 

The failure: Upon power up, the TPS65251 over heats and shuts down. We find that the 1.8V power is shorted to ground from either the Sitara processor, memory chip, or the TPS65251 itself.

 

The failures are rare, and seem to only occur when the board is plugged into a live 15VDC supply. If we plug the 15 VDC into the board while off, then power up the external power supply, no issues.

 

We did find one problem with the design, the engineer used a 1M ohm resistor for the Current Limit inputs (RLM, pins 10.21, 1). The TPS65251 data sheets state a maximum resistance of 300K.

 

Could that somehow cause a catastrophic failure downstream on the Sitara processor?

  • 0
    TI__Guru**** 191445 points

    Hot plugging a supply can cause transients that are well above the abs max voltage.  Do you have any input voltage protection?

  • 0 in reply to JohnTucker
    Prodigy 20 points
    John,

    Thanks for the reply.

    This product is designed for DeviceNet. This particular board plugs into a main board that has the appropriate circuits for DeviceNet hot swap. We don't believe its transients, since the main board is used with other products with no issues.

    It seems to be particular to the TPS65251, and only when the boards are plugged into a live DeviceNet network. It is a rare failure, so hard to pinpoint the culprit. However, the failures are the same, 1.8V shorted.

    Do you know what issues could arise if the resistors connected to the RLM pins on the TPS65251 exceed 300K?
  • 0 in reply to Edward Cocciadiferro
    TI__Genius 9550 points

    Edvard,

    The root cause is "hot plug" .

    Add a suitable capacitor on EN2 pin like EN1/3. If the capacitors on ENx are for the power up sequency, you can increase the EN1/3 capacitor's value accordingly.

    Jason