PGA204: Vo1 & Vo2 outputs...

Hello Francis,

This may take a little time looking into. The PGA204 is general used as a programmable instrumentation amplifier. Since you are bypassing the difference amplifier stage, it might be advantageous dual channel precision op amp instead. What is the gain/gains are you using for this application?

Best,

Errol Leon
Texas Instruments
Precision Op Amp Applications

Hello Errol,

I need gain of 1000.

What are the max output current & resistance of the Vo1 & Vo2 outputs ?

Is it necessary or better to insert THS4031 between Vo1/2 outputs and differential analog inputs of the ads1278 (PGA281 datasheet, page 25, figure 50) ?

Best,

Francis.

Hi Francis,

are you using only a fixed gain of 1000? If that is the case, it is not necessary to use a programmable gain instrumentation amplifier, but like Errol already mentioned a dual channel precision op amp instead.

Regarding the max output current & resistance of the Vo1 & Vo2 outputs: page 8 in the datasheet specifies the output current limit with the short circuit current as shown in the attached figure.

You should consider using a buffer amp between your gaining op amp and ADS1278 for a maximized and reliable data acquisition.

Some thoughts about buffer designs are mentioned in this application report.

Regards,

Miriam

Hi Miriam,

Thanks for your answer.

For me this figure was for the Vo output, so you say that it's for the Vo1/2 outputs too ?

i have choose the PGA204 because he needs less external components, i have strain gauge and i don't have to sort resistances for the gains.

But if you have a reference to propose, i am open :O).

Regards.

Francis.

Hi Francis,

it is a good point that you can save board space with the PGA204. If you can control your switches digitally with your current configuration, you can use that part to save space and use less external components.
The PGA204 uses three op amps of the OPA177 type performance, therefore the current limit should apply for Vo1 and Vo2 as well.

The THS4031 is a possible solution for a buffer. Consider that it is more stable for heavy loads as shown in the datasheet from page 15. Using the THS4031 as a buffer amp with unity gain shows a stable frequency response and 100MHz bandwidth should be appropriate for the ADS1278. Otherwise you can also consider using THS4521 as mentioned from page 38 in ADS1278's datasheet.

Best,
Miriam