Choosing the right ADC for the job

Hi,

We are looking into this. we'll get back to you as soon as possible.

Thanks and Best Regards,
Chris

Hi,

Regarding your requirements, I would recommend the AD7794/AD7795. These parts are 24/16 bit resolution sigma delta ADC's with 6 differential input channels. These parts feature a programmable current source for RTD applications and come in 24- lead TSSOP packages.

For the schematics, you can refer to the EVAL-AD7795.

Hope this helps,

Thanks and Best Regards,

Chris

Thanks for the suggestion!

By combining the schematic of the EVAL-AD7795 and the one in the AD7713 datasheet (for the 4wire RTD on page 24) I ended up with this.

Regarding the EVAL one, could you tell me what the 0R resistors are for? Or are they just place-holders?

In the AD7176-2 (page25) example schematic op-amps are used on the AIN inputs, are these necessary for the AD7794?

Do you think my schematic is ok?

Edit: Fixed the link and added some more.

Yes,, I am also wondering about the 0 ohm resisters on a lot of Analog Devices schematics.??? I did see that Panasonic makes 0 ohm resisters... WHY.????

The zero Ohm resistor can be eliminated and a simple trace be used in the final application.

Zero Ohm resistors may be used for a number of reasons. In the case of evaluation boards, they are often used when it is not readily apparent whether a power supply needs resistive decoupling in addition to one or more capacitors. Zero Ohms may be used first and, if there are noise problems, the zero Ohm resistor may be replaced with a resistance of 10 or 20 Ohms (perhaps more, in some cases). Also, users of the eval board may connect that board to other circuitry that may cause noise on the supply line. In this case, having a zero Ohm resistor is nice because the user can simply remove it and put in a higher value resistor to reduce the noise on the supply line to a sensitive circuit.

Other uses for zero Ohm resistors include allowing the removal of a supply voltage somewhere or to allow inserting a current meter when the resistor is removed. Of course, this can also be done with a jumper, which would be easier for the user, but it is more costly and sometimes board cost is more important than being easier. For example, some companies allow buying things for up to $100 from petty cash where it is not necessary to go to the trouble of generating a purchase requisition. Removing a few jumpers and using fewer board layers (where practical) can be the difference between a board being $99 or over that critical $100.

Hi,

Can you share to us your schematic? Seems to it that the link for your schematic doesn't work.

Anyways, the AD7794/5 has an integrated buffer and in-amp, hence, additional drivers are not required.

Thanks and Best Regards,
Chris

Good explanation,,, Thanks as I thought I was loosing it.LOL

Ok, the link: http://i.imgur.com/CVCknp5.jpg

The main idea (for combining schematics) is to use REFIn1 for the 3 general dif inputs and the REFIn2 for the RTD.

Hi,

Your schematics looks good.

Thanks and Best Regards,

Chris

Thanks for verifying!

This question can be considered answered.