LMP90097: What is the optimal Vref for noise performance?

Alan Islas

Part Number: LMP90097

Hi,

I'm planning to use the LMP90097 to measure two sensors: a thermistor and a photoionization detector (PID).

The output of the PID goes to its own amplifier and the output range of that amplifier is -12V to +12V, which I will limit (voltage divider) and filter (op amp active low pass filter).

So basically I can limit to any voltage range.

I'm having a difficult time deciding what Vref value is best for optimal noise performance, 3V or 5V. ENOB is better at 5V but some noise measures, after calibration appear to be better at 3V.

Also would like to confirm that the analog and digital supply voltages can be different, since the AFE will be connected through SPI to a micro with a 3.3V supply. So, for example, could VA=VREF=5V and VIO=3.3V ?

Thanks for the support.

Regards,
Alan

over 2 years ago

0 Alan Islas over 2 years ago

Prodigy 60 points

Apologies, I meant analog voltage supply VA, what is better for noise, 3V or 5V? Planning to set Vref = VA.

+1 Keith Nicholas over 2 years ago

TI__Mastermind 36280 points

Hello Alan,

VREF=5V will, in general, give the best overall performance. Please refer to Tables 1, 2, 3, and 4 for all combinations of ODR and gain.

The noise is about the same in both cases, but depends on use of the internal buffer. The biggest advantage is the wider input range when using the higher reference voltage; the effective resolution and dynamic range will increase as a result.

Regards,
Keith Nicholas
Precision ADC Applications

0 Keith Nicholas over 2 years ago in reply to Keith Nicholas

TI__Mastermind 36280 points

Hello Alan,

Yes, you can set the digital supply independent of the analog supply. VA=VREF=5V and VIO=3.3V will work well.

Regards,
Keith

0 Alan Islas over 2 years ago in reply to Keith Nicholas

Prodigy 60 points

Hi Keith, thank you very much for the help.

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LMP90097: What is the optimal Vref for noise performance?