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TPS65185 Power Up Help

John Kaye
Prodigy 30 points
Other Parts Discussed in Thread: TPS65185

Dear TI,

I need some technical help with the TPS65185 E-Ink PMIC chip.  We are using this part in our  design to power the E-Ink display.  Here's what's happening:
1) Power up the board.  The WAKEUP and PWRUP pins are both low.
2) Drive WAKEUP high via a CPU GPIO pin
3) At this point, we can talk to the chip via I2C just fine
4) To power up the device, 0xBF is written to register 0x01 (ENABLE) - note that I've also tried just writing 0x80 to register 0x01
5) None of the PMIC's power supplies are on and reading register 0x01 returns 0x20 (only V3P3_EN on)
6) Reading the interrupt registers returns 0x00 on register 0x07 and 0x20 on register 0x08.  This indicates that the VN has/had an undervoltage condition.
7) If I look at the VN_SW pin when I enable the PMIC, I can see it toggling, trying to start up the DC-DC converter.  I can see VN start to dip in the negative direction, but it doesn't get very far before the chip gives up.
I've double checked our schematics against the TPS65185 reference design and don't see any issues with the VN circuit (or any others).  I've also measured around the VN and VN_SW signals and don't see any shorts.
Is my power up sequence correct?  Note that due to an error on my part, PWRUP is tied to ground.  Does this cause a problem?  Any help you can give as on where to go next would be much appreciated.
Regards,
John
  • 0
    TI__Intellectual 810 points

    Hi John,

    When the WAKEUP and PWRUP pins are both low you are in a sleep state. The moment you pull the WAKEUP pin high you are in a standby state in which you should be able to communicate with the chip via I2C. However, none of your rails will be up since PWRUP is still pulled low. The PWRUP pin would need to be pulled up to enable your rails. To bring up your rails and be in an active state you need the PWRUP and WAKEUP pins both high. The undervoltage condition will keep you in a standby state were none of your rails are on. I believe your main issue is the PWRUP pin being tied to GND this needs to be pulled high to enable your rails.

    -Ray

  • 0 in reply to Raymundo Hernandez-Toscano
    Prodigy 30 points

    Hi Ray,

    Thanks for the info. If we tie PWRUP to GND and use the I2C register 0x1 to activate the rails, is that sufficient? The spec also states that PWRUP and WAKEUP can be tied together, are there any issues with that? What we're currently experiencing is that the CPU (NXP iMX6SL) resets immediately following activation of the rails.

    -John

  • 0 in reply to John Kaye
    TI__Intellectual 810 points
    John,

    Having PWRUP to GND and attempting to enable the rails via I2C register will not work. Since, you have the PWRUP pin tied to GND you will experience an UVLO fault that forces a reset. You must not tie PWRUP to GND. However, it is okay to tie PRWUP to WAKEUP.

    -Ray