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MUX damage, o/p short to +Ve supply

Hello,

Using 8-channel MUX for 4-20mA current measurement analog module. It is differential input so two MUX one for +Ve lines and 2nd for -Ve lines. O/P of MUX interfaced with INA AD620. There are two models one having ADG508 and 2nd having ADG1408 MUX IC in design but rest is same.

One common observation with both these Analog input module (using ADG1408 or MUX508A) is that, sometimes +Ve line MUX IC get damaged. Damage is such that MUX IC's o/p becomes short with +Ve supply of MUX IC. It is +12V / -12V supply to MUX IC. Also in some case the damage extends up to INA AD620. MUX IC sometimes physically looks intact and sometimes burnt. No any other section damage observed so far.

4-20mA coming from isolated field Transducer having AC voltage and AC current at Transducer's input. Transducer is 2.2KV isolated for i/p to o/p. 4-20mA drop across 250 ohm resistor to convert to 1-5V range and through low pass R-C filter (10K , 0.1uF) in both +Ve and -Ve line of this signal pass through MUX IC. Total 8-such input channels there.

Need some help to understand failure condition.

Thanks.

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  • Hi Jatin,

    The ADG508A or ADG1408 switch inputs cannot exceed the power supply rails so there is a risk of damage if the input voltage is higher than expected or if the power supply turns off while switch inputs are still present. The abs max ratings of the part will be exceeded.

    It looks like there's a 20k resistor is series with the switch inputs which would help limit any current to the part during an overvoltage condition, but may not protect against all damage. What input voltage can the part see in powered and unpowered conditions?

    The ADG5404F or ADG5248F are 4:1 and 8:1 multiplexers which recently released. They are latchup immune and provide input protection up to +/-55V in powered and unpowered states.

    The ADG508F is an older fault protect part which is also latchup immune and protects to -40V/+55V. The ADG508F is pin compatible with the ADG508A.

    Rgds,

    Paul

Reply
  • Hi Jatin,

    The ADG508A or ADG1408 switch inputs cannot exceed the power supply rails so there is a risk of damage if the input voltage is higher than expected or if the power supply turns off while switch inputs are still present. The abs max ratings of the part will be exceeded.

    It looks like there's a 20k resistor is series with the switch inputs which would help limit any current to the part during an overvoltage condition, but may not protect against all damage. What input voltage can the part see in powered and unpowered conditions?

    The ADG5404F or ADG5248F are 4:1 and 8:1 multiplexers which recently released. They are latchup immune and provide input protection up to +/-55V in powered and unpowered states.

    The ADG508F is an older fault protect part which is also latchup immune and protects to -40V/+55V. The ADG508F is pin compatible with the ADG508A.

    Rgds,

    Paul

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