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ADS1015: Leakage issue for ADS1015?

Jason Chien42
Expert 1180 points
Part Number: ADS1015

Dear Sir:

              We have some leakage issue of ADS1015 when AIN turn on earlier than VDD. As below schematic and picture. When P12V_STBY_PSU2 turn on earlier than P3V3 , There have 450mV leakage voltage from AIN to VDD , When we remove R1003  then leakage voltage will release such as below wavefrom.(Green line is P12_STBY_PSU1 ,Blue line is P3V3 and Pink line is P12VSTBY_PSU2). Our turn on sequencing is  P12VSTBY_PSU2==> P12VSTBY_PSU1==>P3V3. Would you kindly help clarify this issue and do you have some suggest to us? BTW, Can we to know Max forward voltage(vf) for internal diode of ADC?

  • 0
    TI__Guru* 94285 points
    Jason,


    The maximum input current for the ADS1015 is listed in the Absolute Maximum Table on page 6 of the datasheet. The current is maximum 10mA of for any input pin.

    If you are applying voltage to one of the other pins first, then the current will flow into the pin, through the protection diode to either the device, or to the supply the device is connected to. In this case, it looks like the P12V_STBY_PSUx supply is pulling up on the VDD supply. The amount that the VDD supply is pulled up likely depends on the ability of the 3.3V supply to sink current.

    At this point are you damaging the device? It looks like the series resistor is 10kOhms. I would guess that this series resistance is high enough to prevent damage to the device. However, I’m not sure you can do much to stop an external supply from lifting up on the 3.3V supply when there is no power applied to the device. I would say that the best solution is to turn on all the supplies at the same time, or turn on the 3.3V supply first.


    Joseph Wu
  • 0 in reply to Joseph Wu
    TI__Guru* 94285 points
    Jason,


    I just realized that you asked for the expected max forward diode voltage instead of the max forward current. I don’t know of any data for that typical or max value.


    Joseph Wu