AD5422 - Transient voltage protection

Hello,

we want to use the AD5422 in single supply mode (AVDD=17VDC) with voltage and current output on same terminal.

There is a input protection example in the datasheet of the AD5422 (page 37, figure 76).

Right at the input terminal we want to use a bi-directional TVS SMBJ18CA. We also use a current limiting resistor 18 Ohm.

At the input of the AD5422 we have two protection diodes to AVDD and GND.

 

What kind of diodes should be used there (type and power rating) ?

Do I have to use schottky diodes or can I use normal silicon diodes, e.g. LL4148 ?

Should I take care of the higher reverse current when using schottky diodes ?

What is the clamping voltage of the AD5422 internal ESD protection diodes ?

Is another resistor necessary between external clamping diodes and the AD5422 input ?

 

Regards

Parents
  • Hello,

    thank you for the quick response.

    We are using the OP2237 with single supply. The output of the OpAmp can swing to withing 10mV of ground.

    So with the clamping voltages of the AD5422 I think it is better to use a Schottky diode or a normal silicon diode plus resistor, as you mentioned.

    But is the higher reverse current of a Schottky diode a disadvantage ? Is this an additional error in the current output during normal operation ?

    I'm wondering the BAS70-04 used in the application CN0321  can withstand the power dissipation. There is a TVS diode used (SMBJ26CA) with breakdown voltage of 29-32V.  So with a voltage AVDD of 15V there are still 17V for the resistor and the protection diode.

    Regards

Reply
  • Hello,

    thank you for the quick response.

    We are using the OP2237 with single supply. The output of the OpAmp can swing to withing 10mV of ground.

    So with the clamping voltages of the AD5422 I think it is better to use a Schottky diode or a normal silicon diode plus resistor, as you mentioned.

    But is the higher reverse current of a Schottky diode a disadvantage ? Is this an additional error in the current output during normal operation ?

    I'm wondering the BAS70-04 used in the application CN0321  can withstand the power dissipation. There is a TVS diode used (SMBJ26CA) with breakdown voltage of 29-32V.  So with a voltage AVDD of 15V there are still 17V for the resistor and the protection diode.

    Regards

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