ADS1605: Recommended input circuitry for unipolar single ended input

Joaquin Lopez contreras

Part Number: ADS1605
Other Parts Discussed in Thread: ADS1675, TMUX6119, OPA211

Hello all,

I am working in a design with the above reference. Due to the lack of experience in the analogi world I have a doubt on how I should suppy the input to the ADC

My input is a 0-10V coming from an analog sensor.

In my understanding the ADC range is +-3.78V for VREF=3V (pag 17).

According to the datasheet the analog inputs must be driven differentially to achieve optimun performance and two examples are given for single ended and differential signals (Fig.10 and 11).

So my Input signal is unipolar and single ended but I need to transform it to a singled ended bipolar to get into the driver circuit (Fig 10, single ended input recommended circuit).

My question are:

- how I can modify my input to get into the driver circuit? any application note? what should I do?

- On the other hand, there is not any EVM board available for ADS1605 (maybe is obsolete) , is there any way to get one?

Thanks in advance.

Joaquín.

over 4 years ago

0 Keith Nicholas over 4 years ago

TI__Mastermind 40860 points

Hello Joaquín,

You can use a fully differential amplifier to convert 0-10V to +/-3.78V with a 2V common mode, as required by the ADS1605.

Below is an example circuit that will give the required results.

If you have additional questions on how this work, please view the TI Precision Labs - ADC's for more details.

https://training.ti.com/ti-precision-labs-adcs-driving-sar-adc-fully-differential-amplifier

We do not have any evaluation boards available for the ADS1605. The ADS1675 supports 4MSPS and has a full evaluation kit available.

Regards,
Keith Nicholas
Precision ADC Applications

0 Joaquin Lopez contreras over 4 years ago in reply to Keith Nicholas

Intellectual 440 points

That is great Keith!

Thank you very much, you have save me a lot of work.

Just let me ask a final question that I forgot to mention in my first question.

I have two sensors (0-10V) and I am thinking to use a multiplexor to choose the input to the ADC...Any recomendation about a multiplexor? Any rereference? Which is the best place for it Just at the inputs?

Thanks in advance,

Joaquin.

0 Keith Nicholas over 4 years ago in reply to Joaquin Lopez contreras

TI__Mastermind 40860 points

Hi Joaquin,

Since you only need 2 inputs, the TMUX6119 should work well, supporting up to +/-16.5V inputs.

https://www.ti.com/product/TMUX6119

Also, these precision switches have a somewhat high Ron (120ohm for TMUX6119). It would be best to place the switch between the input resistor divider and the OPA211 noninverting input.

Please keep in mind that the ADS1605 is a delta-sigma ADC with internal digital filter. This filter requires 47 output samples to fully settle to a step input, which is created when using a multiplexor.

Regards,
Keith

0 Joaquin Lopez contreras over 4 years ago in reply to Keith Nicholas

Intellectual 440 points

Hi Keith,

Thank you very much for your support!

Everything clear now.

Regards,

Joaquin.

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ADS1605: Recommended input circuitry for unipolar single ended input