How to add HART modem function with ADS8688/ADS1261 and DAC8775

user4786735

Intellectual 460 points

Other Parts Discussed in Thread: DAC8775, ADS1260, ADS8688, DAC8742H

Hi Dear

Reference document tidubi1 and tidueg0.

May I use ADS8688 to replace ADS1262. have any design document to reference?

Q2.

Have any reference to help me to design HART modem with DAC8775 and DAC8472H?

Shawn

over 6 years ago

0 Cynthia over 6 years ago

TI__Mastermind 25020 points

Hello,

The ADS8688 is vastly different from the ADS1260 used in the TI Design.
Thd ADS8688 is a SAR device, that is only 16 bits resolution with a higher sampling rate, while the ADS1260 is a 24 bit resolution device with a max sampling rate of 40kSPS.
If you share why the ADS1260 is not a good fit and what your requirements are, we can help find a replacement part.

0 user4786735 over 6 years ago in reply to Cynthia

Intellectual 460 points

Hi Cynthia

my spec is 16 bits resolution. so I select ADS8688.

It's can be use in HART MODEM?

any reference design?

Thanks

Shawn

0 Christopher Hall over 6 years ago in reply to user4786735

TI__Mastermind 44680 points

Hi Shawn,

Here are our HART modem reference designs: http://www.ti.com/reference-designs/index.html#search?keyword=HART%20modem

However we also have some blog posts and trainings you can reference. I didn't see anything specific to the DACs you mentioned though.

I don't see any reason why you wouldn't be able to use the ADS8688, but you might also look at other devices: http://www.ti.com/data-converters/adc-circuit/precision-adcs/products.html#p84=16;16&p593max=0.015;500&p1028=1;12&p2192=PGA&o4=ACTIVE

If you can let us know what other system requirement you have we can help you choice the ADC that is a best fit. Do you know what kind of data rate you need and if perhaps a SAR or Delta-Sigma ADC is preferred?

0 Garrett Satterfield over 6 years ago

TI__Expert 5820 points

Hi Shawn,

Just to answer your second question, we do not have a reference design for DAC8775+DAC8742H for HART enabled AO. It is quite simple to couple the HART signal into the current output of DAC8775. See section 8.3.15 of the DAC8775 datasheet. The output of the modem can be AC coupled to the HARTIN pin of DAC8775. You could test this with the EVMs of both devices. Ensure that the HTEN bit is set in the configuration register of DAC8775 to enable the HARTIN pin.

Let me know if you have additional questions.

Thanks,
Garrett

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How to add HART modem function with ADS8688/ADS1261 and DAC8775