LM334: LM334M out ripple lead to inaccuracy for ADC read

dengshan yang

Part Number: LM334
Other Parts Discussed in Thread: ADS131M08

hi team,

we're using your LM334M and ADS131M08 for our design as below, we set up LM334M Iout=36uA, when we have the load NTC =10K with 4 wire mode connected to JP5, we found that we couldn't get accurate value for NTC in ambient at 26℃, the read value is about 8.9K, so we will get 2-3℃ tolerance, it can't meet our requirement.

we measure the LM334M output(R19), we found gilter, the waveform is below, could you help check out why?

Jerry

over 3 years ago

0 Ben C over 3 years ago

TI__Mastermind 39475 points

Hi Jerry,

The scope shot looks like there is noise being injected or coupled into the application. Is it possible that you can re-take the scope shot and turn off any clocking circuits? Are you seeing this issue with the other LM334M outputs?

Ben

0 dengshan yang over 3 years ago in reply to Ben C

Prodigy 155 points

hi Ben,

Ben C said:
The scope shot looks like there is noise being injected or coupled into the application. Is it possible that you can re-take the scope shot and turn off any clocking circuits? Are you seeing this issue with the other LM334M outputs?

all othter LM334M outputs is same, we tried, what do you mean "turn off any clocking circuits"?

Jerry

0 Ben C over 3 years ago in reply to dengshan yang

TI__Mastermind 39475 points

Hi Jerry,

The scope photo looks like there is switching noise being introduced into the system. I see this in your schematic:

What is this a crystal oscillator circuit? If so, what is the clock frequency?

Ben

0 dengshan yang over 3 years ago in reply to Ben C

Prodigy 155 points

hi Ben,

it's 8MHz crystal.

0 Ben C over 3 years ago in reply to dengshan yang

TI__Mastermind 39475 points

Hi Jerry,

Is the crystal oscillator running when you are taking measurements? I still would like to understand where the "noise" is being injected into the system.

Ben

0 Ben C over 3 years ago in reply to Ben C

TI__Mastermind 39475 points

Hi Jerry,

Are there any updates?

Ben

+1 Ben C over 3 years ago in reply to Ben C

TI__Mastermind 39475 points

Hi Jerry,

If there are no further questions, can you close the thread by clicking on "resolved"? Thanks!

Ben

Power management

Power management forum

LM334: LM334M out ripple lead to inaccuracy for ADC read