ADS8688: 4 Channel RTD Measurement

user5223639

Prodigy 90 points

Part Number: ADS8688
Other Parts Discussed in Thread: TIPD166

Hi,

I want to measure 4 channel RTD with ADS8688.

In TIPD166 reference design only 1 RTD is measuring with ADS8688 AUX input channel.

Can I use PGA inputs to interface 4 channel PT100 RTD sensor outputs?

I will design external 4 channel current source circuits to drive each RTD. And I will use CM and DM mode RC filters at ADC inputs.

Thanks.

over 2 years ago

0 Dale Li over 2 years ago

TI__Mastermind 39445 points

Hi user5223639,

The TIPD166 reference design selects the auxiliary channel of the ADS8688 for the temperature input because this specific channel has a lower full-scale input range of VREF (4.096 V) than the AVDD power supply. If you want to use other channels with PGAs, ADS8688A (8-ch) or ADS8684 (4-ch) can be a good option because these two ADCs have a same structure but more input ranges including unipolar or bipolar +/-5.12V, +/-2.56V and +/-1.28V.

You may also consider Delta-Sigma ADCs with integrated IDAC currents which can eliminate the need of external current sources, please see ADS124S08 (24-bit) and ADS114S08 (16-bit) datasheet. These ADCs also support true differential inputs and have more benefits to reduce or cancel the errors which are caused by the IDACs and voltage reference. We do have a lot of circuit books or application notes to introduce RTD solutions based on these ADCs, please see some of them below:

Three-Wire PT100 RTD Measurement Circuit With Low Side Reference and One IDAC Current Source

Four-wire PT100 RTD measurement circuit with low-side reference

Two-wire PT100 RTD measurement circuit with low-side reference

A Basic Guide to RTD Measurements

Best regards,

Dale

Because of the holidays, TI E2E™ design support forum responses will be delayed from Dec. 25 through Jan. 2. Thank you for your patience.

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ADS8688: 4 Channel RTD Measurement