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ADS114S08B: Overdriving affects

Jacob Powell
Prodigy 80 points
Part Number: ADS114S08B


Hello,

The last sentence on page 23 of the datasheet says, "Overdriving an unselected input on the device can affect conversions taking place on the other input pins." 

We are limiting the input current to 5mA with a series resistor, in our design, and I am wondering how overdriving one pin can affect the other data conversions, and if we need external Schottky clamps as well?

Also, if we use a 3-terminal voltage regulator to power the chip will we need to add a resistor so that the voltage will not rise when the current rises?

Thanks

  • 0
    TI__Guru** 113765 points

    Hi Jacob,

    If the ESD cell within the ADS114S08B conducts, then there is an internal current inside of the device that is unintended.  This is considered as operation outside of normal operating conditions.  As the undesired current has to travel through the IC, this can affect internal biasing and how the various internal nodes see AVDD.

    Limiting current only prevents the IC from severe damage.  Obviously limiting the current is important.  Current flowing into the analog input pins means that an overvoltage condition is driving current into the device.  Usually this would be caused by very short duration transients and may require external protection from external diodes or clamps.  The ESD circuitry inside of the ADS114S08B is not designed to handle these types of transients.  The ESD events the device is designed for are with respect to normal handling during manufacturing of the circuit board assembly and are usually limited to a few kV.  The specific information for this device is given in the datasheet on page 5 in section 7.2.

    It is not clear what you mean by a 3-terminal voltage regulator, so I'm not sure where you were intending to place a resistor.  This could be a shunt regulator similar to using a zener diode.  I highly recommend using a quality linear regulator such as an LDO type.  This type of regulator should be able to handle transients of reasonable current.  The important thing to remember is you really want to prevent transient current from getting into the ADC which in turn affects the supply.

    Best regards,

    Bob B