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AD5420 FAULT issue

Question asked by TopGunPk on Feb 5, 2013
Latest reply on Feb 9, 2013 by TopGunPk

Hello. I am consulting for a client based in US. We have designed a device for them that is based on a D/A converter (AD5420), which is supposed to output a 4~20 mA signal to a variable valve to regulate pressure and flow.

 

Electronically, I am using a FT4232H USB to SPI converter to send data via the PC's USB port to the AD5420. With this setup, I have been able to successfully communicate with the AD5420, issue it a RESET command and write data to its internal Data registers, and see a respective current output from the DAC.

 

The present problem I am facing is that the /FAULT line activates, and upon reading the Status register, I see a code of 7 (decimal) - indicating :

a) Over temperature,

b) Slew-rate in progress,

c) IOut fault.

 

The circuit is built AS indicated in the Application notes and AD5420 datasheet - no change, except that I am presently not using an External Rset resistor. The Control register has thus been programmed to use the internal Rset resistor.

 

The AVdd line of the D/A is powered by 12V linear supply (the datasheet specifies a range from 10.8V to 20+ volts). So that is in spec too.

 

On the output, i am using a PBSS8110Z NPN transistor with a Breakdown voltage of 100V, so that is in spec too. After that, I am using a 100 Ohm current shunt resistor from the Output to Ground, and measuring signal in Volts on a DMM.

 

Can you please help me ascertain what might the problem be? The product is almost in the finalization stages and BOM is to be ordered.

 

Thank you for your help.

 

Warm regards,

Zeeshan

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