Gain setting in AD8216

Hi Nidhi P Shetty,

I think it's possible. But you should understand that this is only possible by adding external resistors, which are highly likely to spoil the good performance of this amplifier.

First, the value of the external resistors can be calculated using some assumptions. From the datasheet, we can conclude that the resistance of one branch of the input attenuator is 100 kilohms. From the expression for total gain, we learn that for a unity gain, the transfer coefficient of the input attenuator should decrease by 3 times and be 1/54. According to my calculations, adding two resistors of 200 kilohms in series with the inputs should satisfy this.

Second, since you have samples, you can make a layout and use an external potentiometer added in series with the input to find out the experimentally necessary value of additional external resistors.

Third, you can expect someone here to tell you the value of these resistors or suggest an alternative.

Regards,

Kirill

Hi Nidhi, 

I would echo what Kirill has said. The internal resistor ratios of the AD8216 have been trimmed for high precision, and changing up the gain network could severely degrade the accuracy of the device. 

Could you give me more information about your application? Perhaps we can find a better amplifier for you. We do have a couple of other difference amplifiers that can be configured in a gain of 1, like the AD8276. What input common mode range does your amplifier need to accept?

Thanks, 

Kris

Hi Kris

I'm using AD5420 and AD5421 in my design.(for 4-20mA current output configuration)

For self diagnosis purpose I need to sense current from these DAC which I'm performing as mentioned below.

1. In AD5420 sensing is done between it's R3 sense and BOOST pin.

2. In AD5421 sensing is done between it's LOOP- and COM pin.

If we check internal architecture of both AD5420 is with high side sense resistor, higher common mode voltage and voltage will be positive

But AD5421 is with low side sense resistor and  and voltage will be negative.

Hence I need an optimistic solution (Self Diagnosis ADC) to sense current through these pins and process it

Regards

Nidhi P Shetty

Hi Nidhi, 

I would recommend you check out the LT6375. It is a difference amplifier that can be used for current sensing, which has a wide input common mode voltage range (accepts both positive and negative voltages). It can also be configured in a gain of 1, so it should be a good fit for your application. 

Let me know if this works for you. 

Thanks, 

Kris

Hi Kris.

I've used LTspice XVII to understand LT6375 functionality. With the schematic that I've drawn I'm getting expected output.
But I wanted know whether my understanding is correct. That i, whether schematic representation for AD5420 and AD5421 sense output / LT6375 input (highlighted in Blue) is correct?

Snapshots for schematic and plot files is attached.

Please confirm whether my understanding on schematics what I have drawn is correct.

Regards

Nidhi P Shetty

Hi Nidhi, 

From the side of the DAC, it looks like you've got the right idea. Were you intending to use a gain of 0.167? For a gain of 1, REFA and REFB should be floating. Page 22 of the datasheet will give you the configurations. Other than the gain setting though, the schematic seems to be correct. 

Thanks, 

Kris 

Thank you for your support.