AD5421 + AD5700-1 wrong loop current and lack of modulation

additional info.

Customer have to use external regulator ADP2360 because of high consumption os scheme. Censor consumes 10 mA peak current every second (0.8 Hz), to compensate this, customer added three big capacitors to input of adp2360.

additional info.

Customer have to use external regulator ADP2360 because of high consumption os scheme. Censor consumes 10 mA peak current every second (0.8 Hz), to compensate this, customer added three big capacitors to input of adp2360.

Hi, 

Can you check if you still see the ~400mV DC offset on CIN pin even RTS is high?

I also observed that the VLOOP pin does not have a resistor divider, can you double check if you see any bits set on the FAULT register on AD5421?

Cheers,

Ivan

Hi.

When the RTS is high on CIN pin 440mV DC offset (4,00 mA in the loop).

The VLOOP pin has a resistive divider, but it is not shown in our scheme.

All bits in the FAULT register are set to zero.

Cheers,

Denis

Hi Denis,

May I know what Loop voltage and RLoad are you operating on? 

Eugeny.Ivashenko said:

Also there is no modulated signal in the loop

Do you have an oscilloscope capture of the loop current to check this? Or is there a HART slave/receiver on the loop?

Best regards,

Ian

Hi Ian,

Loop voltage 24 V, Rload 325 Ohm.

We use an oscilloscope.

Here is the voltage waveform on Rload 325 Ohm.

Regards,

Denis

Hi,

The hardware setup looks good to me. What SPI commands do you write on the AD5421? are you using direct readback on the fault register or just the auto fault read on the SDO line?

I would also like to test it out without the big capacitors on the LDO input (this is seen at the REGIN pin too. 

Best regards,

Ian