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ADS7953: ADS7953 application

Nanfang Liao
Intellectual 2085 points
Part Number: ADS7953

Hello Team,

My customer wants to use ADS7953 to monitor battery voltage, they can't choose too small divider resistances because of leakage current, so they choose two 10M resistors. Because there is input impedance of our ADS7953. Our part can't monitor a right voltage.

The Vbat range is from 2.3V to 5V, and they only need to monitor 2.4V voltage. Do we have good solution?

Regards,

Nanfang

  • 0
    TI__Mastermind 22017 points
    Nanfang ,

    We will look into this and get back with you.

    Art
  • 0 in reply to Art Kay
    TI__Mastermind 21685 points

    Nanfang,

    ADS7953 can have 5V input range (Range 2 operation) if +VA is set as +5V and VREF = 2.5V so that 2VREF <= +VA. In that case you can get rid of both the 10M resistors.  See DS snippet below

    Range 2 operation of the device is selected by bit DI06 in Mode Control Register. 

    Customer can still use VBD as +3.3V. He has to supply +VA pins with +5V to take advantage of this. 

    Thanks,

    Vishy

  • 0 in reply to Vishy Viswanathan
    TI__Intellectual 2085 points
    Hello Vishy,

    Yes, when Huawei use 10M resistors, because there is input impedance of our ADS7953. Our part can't monitor a right voltage, so they can't use this solution. Do you have other good suggestion? Thanks

    Regards,
    Nanfang
  • 0 in reply to Nanfang Liao
    TI__Expert 5485 points

    Nanfang

    Do you mean to say ADS7953 reports voltage other than 2.4V when actual input voltage applied is equla to 2.4V.

    If that is the case then it could be due to very high input impedance (10M parallel combination). This may cause settling issues and incorrect reading. Can you please confirm if MUXOUT and ADCIN pins are shorted or you have buffer amplifier in between.

    Also can you ask customer to reduce sampling speed and check the performance. If it is a settling issue then reducing sampling speed should help

    Thanks & Regards

    Abhijeet

  • 0 in reply to Abhijeet Godbole
    TI__Genius 16890 points

    Hi Nanfang,

    Have you been able to show the customer the method to have a 5V input with a 2.5 V reference that Vishy mentioned in a post above?  If they do this, they will not need to use any resistors.

    If they can't use that method, have them use a smaller resistor, maybe 1M or 500k or 250k and see how they work.

    Mike