Author Topic: 14.4V ground reference for ADC (Read 12466 times)

Simon · « **Reply #75 on:** May 30, 2019, 06:37:16 am »

Your reference outputs 10mA, I doubt any DAC input wants moro than that. read carefully any notes about the output capacitor value and type required.

Arjunan M R · « **Reply #76 on:** May 30, 2019, 06:38:39 am »

I was looking at the datasheet and it says input vref impeadance = 165KΩ So 2.048/165K = 12.412µA

Arjunan M R · « **Reply #77 on:** May 30, 2019, 06:39:21 am »

of the dac

Arjunan M R · « **Reply #78 on:** May 30, 2019, 06:40:04 am »

so it will be ok

Simon · « **Reply #79 on:** May 30, 2019, 06:41:23 am »

OK so now just make sure you setup the reference correctly. read the whole datasheet and make sure you pick up on any requirements for your application.

Arjunan M R · « **Reply #80 on:** May 30, 2019, 06:43:09 am »

The DAC has a buffered mode

I didn't read the datasheet carefully

Simon · « **Reply #81 on:** May 30, 2019, 06:50:33 am »

Check your frequency response. Sounds like unbuffered is better and you certainly have the drive for it.

Arjunan M R · « **Reply #82 on:** May 30, 2019, 06:52:49 am »

Quote from: Simon on May 30, 2019, 06:50:33 am

Check your frequency response. Sounds like unbuffered is better and you certainly have the drive for it.

yeah, i will go with the unbuffered mode because it draws very low current and i don't have to overcomplicate the code for no reason.

Arjunan M R · « **Reply #83 on:** May 30, 2019, 06:55:19 am »

I don't understand by checking freaquency response, of the DAC or VREF.
Sorry i don't know what it means
Is it this?

Simon · « **Reply #84 on:** May 30, 2019, 06:58:10 am »

what is that a graph of? the reference or the DAC?

Arjunan M R · « **Reply #85 on:** May 30, 2019, 07:01:42 am »

What is this?
20 V peak to peak

Arjunan M R · « **Reply #86 on:** May 30, 2019, 07:02:22 am »

Quote from: Simon on May 30, 2019, 06:58:10 am

what is that a graph of? the reference or the DAC?

It is the Voltage reference

Arjunan M R · « **Reply #87 on:** May 30, 2019, 07:09:08 am »

Quote from: Arjunan M R on May 30, 2019, 07:01:42 am

What is this?
20 V peak to peak

I think its 10mV/div

Arjunan M R · « **Reply #88 on:** May 30, 2019, 07:15:31 am »

Quote from: Simon on May 30, 2019, 06:35:17 am

Quote from: Arjunan M R on May 30, 2019, 06:32:19 am
Quote from: Simon on May 30, 2019, 06:30:38 am
Your link is brocken, but what you do is look at the output current of the voltage reference in it's datasheet and then look up the input current to the voltage reference pin in the datasheet for the DAC.
No it is working.When you click on it it will automatically download the pdf file

No it was brocken and you just edited it! If that is your attitude good luck learninig electronics. Maybe you want to try lego bricks where everything is made for each other and nothing can go wrong!

Sorry it was a mistake i was trying to add a hyperlink, and i was editing what i posted when you replied.
I didn't know how to add a hyperlink.That's why the link is broken

Arjunan M R · « **Reply #89 on:** May 30, 2019, 07:17:21 am »

What can i do about the noise?
Any circuit?

Arjunan M R · « **Reply #90 on:** May 30, 2019, 07:21:10 am »

Found something from TI
Here it is

Arjunan M R · « **Reply #91 on:** May 30, 2019, 07:31:03 am »

But it requires a precision opamp

Arjunan M R · « **Reply #92 on:** May 30, 2019, 07:36:25 am »

Is this enough a 10µF tantulum and 100nF ceramic cap on the output??

Arjunan M R · « **Reply #93 on:** May 30, 2019, 07:44:07 am »

Found this on the datasheet of the VREF.Is this enough for filtering??

Arjunan M R · « **Reply #94 on:** May 30, 2019, 09:42:04 am »

But look what it says on the electrical characteristics.I think it is 10µV/div

Arjunan M R · « **Reply #95 on:** May 30, 2019, 09:54:16 am »

So i think i will stick with this voltage reference.

Arjunan M R · « **Reply #96 on:** May 30, 2019, 10:09:06 am »

Quote from: Simon on May 30, 2019, 06:37:16 am

Your reference outputs 10mA, I doubt any DAC input wants moro than that. read carefully any notes about the output capacitor value and type required.

REF 3120 does not require a output bypass capacitor.Only a supply bypass of more than 0.47µF.
I am going to still add a 10µF tantulum and 100nF ceramic cap to input and output for extra stability and noise reduction.

Arjunan M R · « **Reply #97 on:** May 30, 2019, 10:15:15 am »

IT requires a 100nF cap. for supply bypass.

Simon · « **Reply #98 on:** May 30, 2019, 11:47:50 am »

Yes just follow the datasheets recomendations. You are drawing µA not mA so you don't need to go heavy handed on the output capacitance. Filtering it is not a bad idea.

Arjunan M R · « **Reply #99 on:** May 30, 2019, 11:50:05 am »

Quote from: Simon on May 30, 2019, 11:47:50 am

Yes just follow the datasheets recomendations. You are drawing µA not mA so you don't need to go heavy handed on the output capacitance. Filtering it is not a bad idea.

So i will put only a 100nF bypass cap at the output.


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Author Topic: 14.4V ground reference for ADC (Read 12466 times)

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