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REF5025 for Dual Voltage Generator Problems and ETC.

YoungSik Kim91247
Prodigy 100 points
Other Parts Discussed in Thread: OPA735, ADS1298

Hello,

 

I have a problem on the use of REF5025 and it`s application.

One thing I want to be clear is the output noise that looks like triangle wave from the application TI brahs recommanded.

 

I designed my REF5025 setting like that :

I mimic the application on the page 12 from its spec. with OPA735. 

When I check TP13 - AVSS_2.5V, I watch the triangle pulse on -2.5V baseline like that:

 

I don`t understand this situation, and I can`t use the output as reference.

Could you point out what is problem and why it ocurred?

 

Additionally, I wish to know that the application above is compatible as Analog Voltage Input on ADS1298 or not.

 

Thank you.

 

Kim

  • 0
    TI__Intellectual 2770 points

    Hi Kim,

    You have a lot of capacitive load on the output of the OPA735 (1uF). While this is not an issue for most voltage references (because they are designed for these kinds of loads), most opamps are not stable with big capacitors if you don't use a special compensation circuit.

    Here is one thing I would try: Remove the 1uF capacitor and measure the output voltage again. Your triangle might disappear...

    Are you sure that you want to connect a +2.5V reference and a -2.5V reference voltage to the ADS1298 VREF pins? The datasheet of the ADS1298 mentions that the input voltage range is +/-VREF/GAIN.

    Hope this helps.

    Thomas