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ADS8344 - consequences of stress conditions

Marc Giniaux
Prodigy 10 points
Other Parts Discussed in Thread: ADS8344

Dear all,

We’ve got a question concerning the use of TI ADS8344NB 16-Bits Analog to Digital Converter.

In our design, the ADS8344 is used to monitor a few thermal sensors and the board power supplies (3.3V) through 51 ohms serial resistors (VCC_CONV=5V and MES_V5BOOST=3V):

                       

One of the boards is currently down after a few weeks of operations, and a failure has been identified on ADS8344NB, which is driving much more current than others (around 300mA on 5V power supply), especially on Vref input, which I guess is only a reference voltage and should not driving any current.

We analyzed that during board power up, the power supply sequencing may cause an electrical stress over the maximum ratings during about 1ms, because P3V3ADC input (Green)  is faster than the VCC_CONV power supply establishment (purple):

According to the ADC internal design, what can be the effect of such stress conditions on ADS8344NB? May this be the root of our problems or have any other ideas?

  • 0
    TI__Guru**** 172936 points

    Hi Marc,

    Welcome to our forum!  If the analog input comes up before the power rail of the ADS8344, you could be back driving voltage through the ESD cell.  Generally speaking, we would like to see the current limited to something less than 10mA.  Repeated over voltage/over current can cause premature failure of the silicon structures inside the device.  Is channel 5 just monitoring you digital rail?  Can you add a larger resistor/capacitor ahead of R100 to slow the ramp rate and further limit the current to the pin?