REF5020 noise spec

Shabbir Amjhera Wala

Other Parts Discussed in Thread: ADS8320, OPA353, OPA350

Hi,

We are planning to use REF5020 as a reference input to characterize CT front end device for which integrated noise is a very critical spec. So we want to know REF5020 integrated noise till say 10M. I simulated REF5020 model using TINA and found it reaches to 33uV as shown in below plot which seems to be quite high. So I was wondering whether noise has been modeled correctly or not. So could any one have idea about integrated noise of REF5020 till 10MHz?

Thanks

Regards,

Shabbir

Design engineer

Texas instruments, India

+91-9243532152

over 12 years ago

0 Marek Lis over 12 years ago

TI__Guru 68541 points

Shabbir,

First, the noise performance of REF5020 is a function of a capacitor placed on TRIM/NR pin (see below) where adding 1uF capacitor decreases the overall output noise by a factor of 2. Also, adding RC filtering at the output with corner frequency below ~60kHz will decrease the total noise-see voltage noise spectral density simulation plots below. The REF5020 macro-model provided on TI website may not be precise but is relatively close to correctly simulate the output voltage noise.

I have simulated the REF5020 output voltage noise spectral density with CNR of 0 and 1uF - see results below;

The integrated noise for the two cases is shown below: ~105uV for CNR=0 and ~50uV for CNR=1uF.

Of course, the simulations above do NOT include the effects of any additional RC filtering at the REF5020 output and thus any such additional pole below ~60kHz will result in a decrease of the total noise of REF5020.

0 Shabbir Amjhera Wala over 12 years ago in reply to Marek Lis

TI__Expert 4711 points

Marek,

Thanks for your quick reply. It seems TINA model and your simulation results matches very nearly. Initially we were avoiding putting any filter at the reference output because our device takes some current from reference and because of which putting resistance in the path will introduce some drop in the reference and will result in some error. But it seems we have to put external filter to avoid noise. We will analyze it more and will see possibility of putting any buffer which will provide device current.

Thanks

Regards,

Shabbir

0 Sasa Kojic over 11 years ago in reply to Shabbir Amjhera Wala

Prodigy 50 points

What is a better choice for the reference voltage for the 16-bit ADC converter ADS8320 chip, REF5020I or REF3220 or LM4040A20?

thanks in advance
Sasa

0 Marek Lis over 11 years ago in reply to Sasa Kojic

TI__Guru 68541 points

Sasa,

REF5020 has the lowest noise and lowest drift but nevertheless requires op amp driver for filtering and speed in order to obtain ADS8320's optimal performance. The best op amp for the driver in such application is OPA350 or OPA353 capable of direct driving capacitive load in excess of 10uF.