TLV2542 12-bit ADC issue

Samir Prabhudesai

Other Parts Discussed in Thread: TLV2542

Hi Guys,

I am using TLV2542 in my project. The supply voltage is 4.1V and Reference voltage is 3.3V. Hence the step size is = 3.3/4096 = 0.000805 V. I am expecting that at each mV of i/p voltage the ADC o/p should respond, but in actual case I am getting change approx after each 6 mV of i/p voltage shift. i.e from 0 to 5 mV of i/p I am getting 0 as o/p, from 6 to 10 mV I am getting 6mV as o/p and so on. I am getting correct values of o/p but within a tolerance of about 5-6 mV but my expected resolution is 1mV.

I am reading the o/p of ADC in bit-banged way with SCLK running at 500 KHz.

Can anybody pls give me some hint?

over 13 years ago

0 Tom Hendrick over 13 years ago

TI__Guru**** 171096 points

Hi Samir,

Can you possibly post the TLV2542 portion of your schematic showing how you have the inputs configured? Are you applying the same input voltage to both channels of the TLV2542? What are you using as a source to provide the 1mV input steps?

0 Samir Prabhudesai over 13 years ago in reply to Tom Hendrick

Prodigy 50 points

Hi Tom,

Thanks for replying. Both analog channels are shorted and supplied i/p using a 1.2V Battery and a 20K pot. I am monitoring the i/p voltage supplied using a well caliberated multimeter, but the i/p changed by 1 mV is getting reflected only on meter but not on ADC o/p.

I will post the schematic portion once I reach my office.

0 Tom Hendrick over 13 years ago in reply to Samir Prabhudesai

TI__Guru**** 171096 points

Hi Samir,

Please do send along the schematic, I'd like to understand exactly how you are driving the ADC inputs. More often than not, problems getting the correct conversion results can be attributed to the input drive. The TLV2542 is a successive approximation register (SAR) converter. The device really should have a low impedance input and your 20K pot may be part of the problem. Have you tried putting an op-amp buffer between the pot and the ADC? Take a look at this presentation, it might help a little.

0 Samir Prabhudesai over 13 years ago in reply to Tom Hendrick

Prodigy 50 points

Hi Tom,

Pls check the attached schematic. In this I have taken ref voltage as 2.7V. I will try the buffered i/p suggested by you and get back to you.

Pls pass on any additional information you come across.

5040.TLV2542.pdf

Regards,

Samir

0 Tom Hendrick over 13 years ago in reply to Samir Prabhudesai

TI__Guru**** 171096 points

Hi Samir,

Along with the buffer, please add some capacitance to the REF pin - at least 1uF. Keep the ground leads as short as possible as well. Is this on an actual PWB or put together with fly wires?

0 Samir Prabhudesai over 13 years ago in reply to Tom Hendrick

Prodigy 50 points

Hi Tom,

Sorry for the delayed response. Actually the board I am using is meant for AD7921 which has different footprint and pinout from TLV2542. Hence I had to solder this IC i.e. TLV2542 with some wires, each wire used is not more than 10mm in length.

Right now I am engaged in some other activity so I would need some time to try out your suggestions. I would get back to you soon.

Regards,

Samir

0 Tom Hendrick over 13 years ago in reply to Samir Prabhudesai

TI__Guru**** 171096 points

Hi Samir,

How is your testing going?

0 Michael W over 13 years ago in reply to Samir Prabhudesai

TI__Expert 3260 points

Hi Samir,

Because of the length of time since last interaction, we will assume that your problem is solved. At least for now.

Regards,

Michael

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TLV2542 12-bit ADC issue