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AD5421 Current always stuck to fix value

Question asked by embedded_ca on Jun 2, 2016
Latest reply on Jun 6, 2016 by embedded_ca

AD5421_Current.JPG

 

As per above diagram, if the MOSFET is in circuit, the AD5421 does not produce any output. If I bypass the MOSFET then when micro is not programmed and 24V is applied to the 4-20mA output loop, the current is 3.2mA as specified by datasheet. When I load DAC with either 0x0000 or 0xFFFF to DAC the output goes to 0.22mA always.

I tried changing the values of OFFSET ADJUST REGISTER and GAIN VALUE REGISTER but has no impact on the values.

The voltage at V_LOOP is 0.9V

Voltage at DRIVE: No Voltage (which is bit surprising)

 

I will appreciate any clues.

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