AD5421 Power On Reset

Hi,

The AD5421 powers on with all registers loaded with their default values and with the loop current in the alarm state set to 3.2 mA or 22.8 mA/24 mA (depending on the state of the ALARM_CURRENT_DIRECTION pin and the selected range).

The most pins that you mentioned are input pins in a sense that the part will power up and will set settings of the part depending on the values of these pins.

Regards,

Mark

Hi,

 I am Using this AD5421 in 4-20 mA mode.

Ans I am not able to set current less than 6.5 mA but above 6.5mA i am getting all the values.

Please let me know what is the issue.

Thanks 

Anush

Hi Anush,

Are you using the internal voltage regulator to supply other components? The maximum current that can be drawn from the REGOUT pin should only be 3.15 for you to be able to set the loop current to 4mA. I'm thinking that in your circuit you are drawing 6.5mA from the regulator so you can only set loop currents greater than this value.

Best regards,

Rainier

Hi,

Thanks for your reply.

Yes, Iam using the power from DVCC pin to power up the isolators and the HART modem AD5700.

As per Current  calculation the total current taken by the isolators ADuM1441 will not exceed 3.15mA.

I have attached the schematics for you reference.

Hi Anush,

The text on the schematics is hard to read. Can you provide better images?

Best regards,

Rainier

Hi Anush,

The text on the schematic is still not clear. I can't read the components used.

PDF

Hi Anush,

Considering the maximum supply current drawn from the DVDD of AD5421.

• LTC2484 = 250uA
• ADUM1441 = 900uA (x4)
• AD5420 = 1mA
• AD5421 IOVDD = 300uA

These would already be equal to 5.15mA. We haven't even added the current drawn from the pull-up resistors, LEDs etc.

Best regards,

Rainier

Hi Rainier,

Thanks for your reply.

I have removed all the pull-up resistors that were there near the isolators.

Now I am getting 3.12mA current when I give the eternal 24 V supply.

It is working now.

Thanks & Regards

Anush