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TPS55289: What conditions would result in i2c interface not responding

Gordon Charles
Prodigy 10 points
Part Number: TPS55289

Tool/software:

I have a design with the Schematic, BoM and layout largely lifted from the TPS55289 Buck-Boost Converter Evaluation Module User's Guide, https://www.ti.com/lit/pdf/slvucf2. After power up i2c access is met with a NAK (which is the equivalent of the part not responding). The boards are machine assembled and I've buzzed on two boards for shorts and found no issues.  Two boards both behave in the same manner.  In this application the input power is a 5V/3A rated supply and the maximum expected load is 0.8A @ 7V.  VIN.  

I've verified the voltages on:
VIN (4.92V)
EXTVCC (4.92V)
VCC (4.90V)
EN / VLDO (1.77V)
MODE (0V)

I've verified all of the timing requirements for the i2c interface as easily being met.  I'm running the bus at 100kHz.  Here's a scope trace of the first byte (address = 0x75 + write bit:

Decoded version on logic analyzer as a sanity check:

Could you please provide a list of potential other issues that would prevent the device from responding or other items to check to determine the state of the device?

  • 0
    TI__Genius 14870 points

    Hi Gordon,

    Thank you for reaching out. About the schematic, I want to remind that MODE pin is 6V rated, so don't connect to VUSB2 directly(I know it is DNP now).

    We have two points to check now:

    1. Can you help check if SCL and SDA are connected reversely? 

    2. Please use your current program to communicate with other device with I2C function to check if the program is correct.

    Regards,

    Mulin

  • 0 in reply to Mulin Yuan
    Prodigy 10 points

    Mulin,

    Thanks for the help.

    A1) I've checked before and checked again, the signals are not swapped.

    A2) I've communicated with an other device and the software is correct (although - it really should not matter as the waveform shows both the stimulus and the NAK response)

    Note: VBUS is rated 5V @3A with a maximum voltage of 5.5V, so connecting the MODE pin should not be an issue. 

    Regards,

    Gordon

  • 0 in reply to Gordon Charles
    TI__Genius 14870 points

    Hi Gordon,

    Can you help confirm version of IC, whether it is TPS55289 or TPS552892?

    Do you have TPS55289 EVM board? You can check if the program can communicate with EVM.

    Regards,

    Mulin

  • 0 in reply to Mulin Yuan
    Prodigy 10 points

    Mulin,

    The assembly house mistakenly ordered TPS552892.  Once the correct part was installed it functioned as expected.  I would strongly encourage you to provide feedback to marketing manager responsible for selecting the part number.  While the mistake here falls on the assembly house for making the error and myself for missing the error in review, in my experience functionally different footprint compatible parts have different part numbers with the same number of digits, not be extending the part number by a digit.  Typically additional characters beyond the base part number define, different packages, temperature ranges or in rare cases support for different software.  In my opinion, TI's choice to differ from the norm increased the probability of the error occurring.