AMC1311: 250VAC / 400Hz isolated voltage measurement

ali kelem

Intellectual 400 points

Part Number: AMC1311
Other Parts Discussed in Thread: TLV9152, AMC1301, TLV9004, LMV324, OPA191

Hi,

I want to design 250VAC/400Hz isolated voltage measurement as seen concept below.

Can I control 1V offset voltage by using a buffered DAC in that design?

Any recommend?

Thanks.

over 5 years ago

0 Alexander Smith over 5 years ago

TI__Guru 55342 points

Hi Ali,

This will work but I have a few comments.

1. Size of shunt resistor. Depending on what type of transients and range you would like to see, you may want to adjust this from 10k. In example, 8.03k would utilize the full-scale range of 0-2V for a 250Vac input.

2. The I2C lines for the DAC will need a digital isolator to communicate over the isolation barrier with the MCU.

3. The second opamp will need to be rail-rail compatible if using a 3.3V supply and expecting a 3.3V output.

4. If using a psuedo-differential ADC, you will also need 1.65V for the negative input, as shown here: http://www.ti.com/lit/an/sbaa317/sbaa317.pdf

If using a single-ended ADC, disregard comment #5.

0 ali kelem over 5 years ago in reply to Alexander Smith

Intellectual 400 points

Hi Alexander,

Regarding to your comments;

I've tried to make a simulation in spice by implementing AMC1311 spice model. ( Sorry not to use TINA :) I'm used to LTSpice. )

I connected 1.65V ext.DC bias but can't get an expected output. It seems approx. 2.15V

Second opamp is rail-to-rail but It 's not behave like first opamp.

If done it, I will have a chance to use 1.65V-DAC reference at second side opamp without isolated. First opamp will has a regular DC bias.

For comment 5 : Yes, using a single-ended ADC in MCU.

Thanks.

Ali

0 Alexander Smith over 5 years ago in reply to ali kelem

TI__Guru 55342 points

Hi Ali,

Try adding a GND node to the low side :)

Let me loop in someone from amps to suggest an alternative to OP191 as well.

0 Former Member over 5 years ago in reply to Alexander Smith

Hello Ali and Alex,

First, I would invite you to take a look at the following Texas Instruments Cookbook circuit document. It highlights the design process for the circuit shown in stage 2 and I think you might find it useful.

As for parts, I've put together the following list. From left to right you'll go from lowest online price to highest online price. Naturally, performance tends to get better as you move toward the right as well. These parts are all "rail-to-rail output." So, you may pick your part depending on how much precision you need. The TLV9152 might be a good place to start, but I would verify that the output swing is sufficient for the application as you may want something that can get slightly closer to the rail.