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TPS55288: Setting OE bit to 1 on TPS55288 is causing registers to reset

Liam Birkin
Prodigy 10 points
Part Number: TPS55288


Tool/software:

Hi, 
I have a circuit with the TPS55288, Vin is supplied by a ~3.7V LIPO battery.

EN/UVLO is above 1.23V via a transistor.
I can communicate with the IC over I2C just fine at 75h.

But when setting the OE bit to 1, all of the registers get reset at the Vout is ~1.85V.
VCC is measuring ~3.4-3.5V.
There is no fault reported on register 07h. It reads as 0x01.

My schematic is attached below.

  • 0
    TI__Guru 67355 points

    Hello Liam,

    Did you check your design with the design calculator SLVRBF9 Calculation tool | TI.com?

    It seems that the device gets reset, did you check the input voltage at the moment when you turn on the output? Is it possible that the device gets into UVLO?

    Best regards,
    Brigitte

  • 0 in reply to Brigitte
    Prodigy 10 points

    Hi Brigitte,
    Thanks for providing that tool, it's very helpful.

    I tried bypassing the 100Ω resistor and mosfet by tying EN/UVLO to Vin so that it remains at ~3.6V, but I am getting the same result where the register values reset when I set the OE bit to 1.

    I have also tried increasing Vin to 5V and the register values will stick when setting the OE bit to 1, however I am not getting the correct output voltage.
    With all of the registers at default values I am expecting 5V out, but am only getting 1.85V out. 

    The only load attached to Vout is an SMD led with a 82kΩ resistor.

  • 0 in reply to Liam Birkin
    TI__Mastermind 28700 points

    Hi Liam,

    Thanks for feedback, we will look into this and reply to you next week.

    BRs,

    Bryce

  • 0 in reply to Bryce Xun
    Prodigy 10 points

    Thanks Bryce.

    I also tried externally supplying 5V to VCC. 
    But I am still having trouble getting the correct output voltage.


    Currently I have:
    Vin = 5V
    EN/UVLO = 5V
    VCC = 5V


    And reading out the registers I get: 
    0x00: 0xD2
    0x01: 0x00
    0x02: 0xE4
    0x03: 0x01
    0x04: 0x03
    0x05: 0xE7
    0x06: 0xAD
    0x07: 0x01

    But the voltage on Vout is only ~ 2.4V.
    I can't seem to get any higher than this, and I can't get it out of buck mode.

  • 0 in reply to Liam Birkin
    TI__Mastermind 18220 points

    Hi Liam,

    L needs to be at least 4.7uH if you choose Fsw=400kHz. And your compensation value looks not reasonable. Please use R34=0Ω, C41=10nF as a start.

    Could you please measure SW1, SW2, Vout, IL waveform when writing OE=1 to see startup waveform?