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HDC2022: The ACK of HDC2022 is occasionally abnormal

Lan
Prodigy 40 points
Part Number: HDC2022
Other Parts Discussed in Thread: TMP112,

Tool/software:

We have attached 2pcs HDC2022 and 4pcs TMP112 to an IIC bus, only the ACK signal of the chip U170 is occasionally abnormal, while the access of the chip U104 and the other 4pcs TMP112 chips is stable, please help to check the waveform of U170(iic addr=0x41).

    

We found that if it's stable if we connect the PIN of VCC/GND to the pad by flying-wire(also set EPAD from GND to float). 

If there any special requirement for the VCC/GND/EPAD?

  • 0
    TI__Expert 4740 points

    Hello Lan,

    Could you please share a schematic of how the devices (specifically the HDC) are connected? 

    Regards,

    Harry

  • 0 in reply to HarryG
    Prodigy 40 points

    Hi HarryG,

    The schematic and layout of U104/U170 are following, we found that U170 access OK after disconnect the connection between the heat dissipation pad of U170 and the GND pin, and then connect the GND pin to the DGND plane.

               

  • 0 in reply to Lan
    TI__Expert 4740 points

    Hello Lan,

    I would suggest to not only leave the thermal pad (pin 7) disconnected like you just did, but also leave it unsoldered from the board entirely. This will also help if you intend to use the heater in your design as it could make it more effective.


    Regards,

    Harry

  • 0 in reply to HarryG
    Prodigy 40 points

    Hi HarryG,

    The thermal pad of U104 and U170 are all connected to DGND by the vias, the difference is connection of GND pin that U104 is connected to DGND plane directly but U170 is connected to the thermal pad.

    We doesn't use the heater function, so we solder the DAP to DGND plane.

    In the rework, we remove the connection between GND pin and DAP pin, and also use a flying-wire to connect the GND pin to DGND plane.

    My question is why does DGND affect IIC communication when it connects to the DGND plane via DAP?

  • 0 in reply to Lan
    TI__Expert 4740 points

    Hello Lan,

    Is there any particular reason U170 has a different layout than U104? There might be a chance that due to U170's layout, the GND pin is never grounded which might be causing functionality issues in the device. I would recommend implementing U104's layout for U170 as you are asserting ground to the GND pin more directly.


    Regards,

    Harry 

  • 0 in reply to HarryG
    Prodigy 40 points

    Hi HarryG,

    The GND pin of U170 is also grounded through DAP, I think GND pin can be connected to DGND plane through DAP according to the datasheet. 

  • 0 in reply to Lan
    TI__Expert 4740 points

    Hello Lan,

    This is correct, but the thermal pad would still require a trace from a via that's connected to ground to properly ground the HDC2022. In the datasheet photo for example, the thermal pad is being grounded by the trace running from the grounded side of the capacitor.

    Regards,

    Harry