MSP430FR6043: Input stage design

Kostyantyn Shvydkyy

Part Number: MSP430FR6043
Other Parts Discussed in Thread: OPA836, TIDM-02003, OPA607, OPA357, TIDA-01486, OPA838

Hi,

I am currently finishing the design of the input stage for MSP430FR604*.

It looks as on the image below:

The transducers are operated at 1MHz, sampling at 4MHz.

I have a few questions:

Which op-amp (U1) would you recommend for best zero flow performance? The candidates that I am currently looking at are OPA836 (as in the gas reference design TIDM-02003), OPA357 and OPA607. The gain is about 5.
Considering that I want a cutoff at around 2MHz, what are the optimal values for R11 and C26?
As far as I understand, this should be dependent on the ADC properties, but I could not find them on the datasheet.
On the TIDM-02003 they are 499 and 680pF (470kHz), but on the TIDA-01486 the capacitor is not present, only an input resistance of about 15Ohm (10 + 5 from the switch).

C36 should still remain 1nF, right?

Best regards,

Kostyantyn

over 3 years ago

0 Leonardo Estevez over 3 years ago

TI__Genius 12615 points

Hi Kostyantyn,

Typically, 1MHz transducers are used for water(not gas). If you are designing for water, I would recommend that you look at making the modifications described here instead:

https://www.ti.com/tool/TIDM-02005

BR,

Leo

0 Kostyantyn Shvydkyy over 3 years ago in reply to Leonardo Estevez

Prodigy 160 points

Hi Leo,

I am fully aware, we are using our own transducers and a custom board in a water application.

For certain reasons that I will not disclose here we cannot connect the transducers straight to the input.

However I have been getting good results with the op amp, with about 50ps drift and 25-35ps standard deviation on DToF, now I just wanted to see how it can be improved further.

Best regards,

Kostyantyn

0 Leonardo Estevez over 3 years ago in reply to Kostyantyn Shvydkyy

TI__Genius 12615 points

Hi Kostyantyn,

We see an improvement in standard deviation for gas using the OPA838. I wouldn't expect to see any improvement in zero flow drift provided that the RC circuits on the Tx and Rx circuits are matched.

BR,
Leo

0 Kostyantyn Shvydkyy over 3 years ago in reply to Leonardo Estevez

Prodigy 160 points

Hi Leo,

Thank you for pointing out OPA838, have not seen that one before!

In your application note on Figure 2 you have the lowpass again.

I will give a few resistor values a test.

Best regards,

Kostyantyn

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MSP430FR6043: Input stage design