ADS8638: DRIVING ANALOG SIGNAL INPUT

Tom-san,

Thanks for your reply.

A customer is considering either the LM358B, OPA2994, or TLV2171 as a voltage follower.

Which do you think is best? The input signal will be ~200Hz.

I think the TLV2171 is best, but what do you think?

The TLV2171 small-signal overshoot vs. capacitive load characteristics are similar to those of the OPA140.

Best Regards,
Ishiwata

Hi Ishiwata-san,

The decision would be based more on the expected data rate at this point.  If you are going to run the ADS8638 at it's maximum speed, the higher bandwidth of the OPA140 would be a benefit at 1MSPS.  I suspect the TLV2171 would be fine with slower data rates - what speed do you expect to be running at?

Hi Tom-san,

Thanks for your answer.

The operating speed is up to about 200Hz.

Ishiwata-san,

You can't capture a 200Hz input signal with a 200Hz data rate, by Nyquist, you have to run at least 400Hz.  Normally folks run at least 10x so you should be looking at 2kHz or higher.

Tom-san,

Thank you for your support.

I will need to confirm with the customer, but I think the SCLK is probably around 200Hz.
I would like to check the actual data transmission speed.
I understand that there will be no problem as long as the data speed is sufficiently slow compared to the SCLK, is that correct?

Yes - please do let us know.  A 200Hz SCLK is not going to be a very efficient way to run the ADS8368 device.

I'll correct that.
I heard the input signal is 200Hz, so I think the data signal will probably be 200Hz.
I think the SCLK is faster, but I will confirm the SCLK frequency with the customer again.

Thank you for your support.

Is it possible to know the TUE for the ADS8638? Do I need to calculate it using a formula?

As noted eralier - root sum of squares is the way to go using the typical numbers for offset/gain/etc. 

Thank you.
I'm sorry, I see you've already answered.

Tom-san,

Thank you for your support.

I apologize for the late reply.

I confirmed with the customer about the clock signal. The clock is 6MHz.
When using it as a voltage follower, which would be best: LM358B, OPA2994, or TLV2171?

Best Regards,
Ishiwata

Thank you for your reply.

If I use the TLV2171 or OPA2994 as a voltage follower in the circuit diagram below, can I use the same resistor and capacitor values?

Yes, that would be fine.