ADS8689: 800Vdc measurement

Ludwig Fichtl

Part Number: ADS8689
Other Parts Discussed in Thread: OPA320, ADS8509

Tool/software:

Hi,

I have a ADC design, based on the ADS8689IPW to measure a +/-800Vdc voltage connected to a 200:1 voltage divider. (We need to measure negative voltages to detect a wrong wiring).

I now found out, that the internal 1Meg input impedance together with the biasing voltage, adds an (nonlinear) offset to my measurement.
After some research I found the TI document "Circuit To Increase Input Range on an Integrated Analog Front End (AFE) SAR ADC", but increasing Rext to 79Meg still adds me an massive fault to my measurement.

Is it possible to measure +/-800Vdc with the ADS8689 or would you recommend a different IC design?
The measurement also needs to be galvanic isolated, therefore the SPI-Interface.

Best regards,
Ludwig

11 months ago

+1 Tom Hendrick 11 months ago

TI__Guru**** 182081 points

Hi Ludwig,

Is adding a buffer like the OPA320 between your resistive divider and the ADS8689 input an option for you?

0 Ludwig Fichtl 11 months ago in reply to Tom Hendrick

Prodigy 50 points

Hi Tom,

yes inserting a Buffer would be an option. I just wanted to shun the effort and expenses like adding an other isolated DCDC for the OPAmps negative rail.
But if it's the only or easiest way to go, we will do it.

Thanks!

Best regards
Ludwig

0 Ludwig Fichtl 11 months ago

Prodigy 50 points

Is it possible to shut off the internal Biasing Voltage?

0 Tom Hendrick 11 months ago in reply to Ludwig Fichtl

TI__Guru**** 182081 points

Hi Ludwig,

Unfortunately no, it is not possible to shut off the bias or bypass the internal LPF. I asked about the buffer since I thought that might be easier on you versus swapping out the ADC and changing your software to accommodate a different part. Speaking of which, the ADS8509 might be an option for you if you want to try a different ADC. That part using pin strapping to get a +/-10V input range on a single 5V supply.

0 Ludwig Fichtl 11 months ago in reply to Tom Hendrick

Prodigy 50 points

Hi Tom,

I did some measurements with a dual voltage supply buffer and it works good.
This seems to be the best way to go.

Thanks!

Best regards
Ludwig

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ADS8689: 800Vdc measurement