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AD5422 Output tied together with other AD5422

Question asked by Photoman on Oct 25, 2016
Latest reply on Nov 11, 2016 by Photoman

I am using a DAC (AD5422) in an application where there is the possibility of a customer misusing this by tying all the analog outputs together, where the outputs are at different potentials, and possibly in different modes (-5V to +5VDC and 4-20mA).  I have use the datasheet op amp example to tie the Voltage output and current outputs together.  My supply voltage to the device is 18-36VDC, so the 4-20mA voltage of one unit could possibly be trying to drive 36V (trying to drive to 20mA), while another unit could be configured as a voltage unit trying to drive to -5V.  The -5V supply is pretty weak, so it will likely current limit and the 36V would win out.  There is an 18 ohm resistor on the Volt/Current output.  I have reverse polarity protection diodes going to the +input and -5V supply, and a 36V TVS on the analog output.

 

 

In the worst case scenario, with 2 or more of these trying to fight each other, would any there be anything destructive happening to the devices?  If so, what would the failure mode be? Included in a worst case scenario would be two units next to each other with a short length of cable (very low impedance), where both outputs are virtually shorted together.  

 

Thanks in advance for your response.

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