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ADS7142-Q1: ADC Low Temp Failure

Deq Hussein
Prodigy 10 points
Part Number: ADS7142-Q1 
We are a US based Automotive company working on Electric Vehicle Chargers and Heaters.

Issue Description:

  • While testing boards with TI ADCs (ADS7142QDQCRQ1) at -20 Degree C or below, we find the I2C data from Channel 1 (AIN1) is the same on Channel 0 (AIN1).
  • The I2C Data on the two channels are different and work fine above -20 Degree C.
  • Channel 0 has High Voltage analog input data (HV_IN_Sense) as shown in the schematic below and he Channel 1 has the High Voltage Current analog input (HV_I_Sense).
  • The High Voltage is connected by unit is not enabled therefore should not have any current showing. The current meter does not indicate any current but the CAN interface data shows current draw.
  • With the unit is the cold chamber around -20 Degree C, we probed a number of input and output pins on components up to pin 4 of U15 and it shows 300mV indicating zero current flow as per the component datasheet. The VCC levels on these ICs were within the normal range. The HV_I_Sense signal measured around 300mV with the element disabled indicating the current is 0A. When the High Voltage line was increased, the HV_I_Sense current values in the CAN interface showed increase in this value. The measured value pin 4 of U15 ADC stayed within 300mV. The schematic below shows points tested. Table 1 below shows data collected.
  • We targeted U15 and sprayed with cold spray and were able to duplicate the problem.

 

 ADC-Current-Measurement Issue-TI.docx




  • 0
    TI__Mastermind 24940 points

    Hello, 

    This is very interesting. Is it possible for the digital communications to be affected at these temperatures, would you please confirm that the digital bus is as expected? a visual inspection of this, using a oscilloscope or other similar tools would help with this. 

    Regards

    Cynthia

  • 0 in reply to Cynthia
    Prodigy 10 points

    We have used scope at the I2C outputs of the ADC and decoded the data and seen the issue at the low temp (-30). We also connected a logic analyzer after the ADC and the decoded data shows the same pattern of both channels having the same data. We grounded Channel 1  with Channel 0 still connected and saw the same pattern at the low temperatures. My engineering analysis tells me the Multiplexer select line may be stuck at Channel 0 selection when the temperature reaches -30C or below. The results are very consistent across 9 boards and we were able to recreate.

  • 0 in reply to Deq Hussein
    Prodigy 10 points

    Clarification: We ground Channel 1. Channel 0 was still connected to the input data as before. We expected Channel 1 data to always be stick at one value and should never be the same value as Channel 0. We found that once the temperatures a certain value around -30 Degree C. Channel 1 follows Channel 0.

  • 0 in reply to Deq Hussein
    TI__Mastermind 24940 points

    Thank you for the information. 

    I believe this would be best handled through direct communication, would it be acceptable for me to contact you at the email your account is registered under?

    Regards

    Cynthia

  • 0 in reply to Cynthia
    Prodigy 10 points

    Email should work. deq.hussein@phillipsandtemro.com

  • 0 in reply to Deq Hussein
    TI__Mastermind 24940 points

    Thank you, I have reached out and will close this thread