ADC121C021: ADC121C021

Aiden Lee

Part Number: ADC121C021

I use two ADC121C021 for sensing temperature.

When I only connected pull down resistor to VIN of the chip, I2C communication is not problem. I2C operate normal.

However, when I connect temperature sensor and read the ADC, there is noise on SDA line and SDA signal not rising at STOP step.

In other words, when a certain voltage level enters the VIN, a problem occurs in the SDA signal.

1) VIN connect GND through resistor(1Kohm) : normal operation

2) noise and not rise SDA signal at STOP step.

3) there is noise on SDA signal, only VIN connect VA through 10Kohm

over 1 year ago

0 Samiha Sharif over 1 year ago

TI__Expert 8615 points

Hi Aiden,

Thanks for your question! Could you please share your schematic? It would help me get a better understanding of your circuit.

Best regards,

Samiha

0 Aiden Lee over 1 year ago

Prodigy 30 points

Hi Samiha,

Below is my schematic file.

0 Aiden Lee over 1 year ago in reply to Aiden Lee

Prodigy 30 points

Additionally, I connect a VR(variable resistor) to J5 for testing and J6 is not connected.

0 Samiha Sharif over 1 year ago in reply to Aiden Lee

TI__Expert 8615 points

Hi Aiden,

Unfortunately, I cannot read anything clearly in this schematic. Could you please upload a higher resolution image? You can also insert the image into a word doc or powerpoint presentation and upload that.

Best,

Samiha

0 Aiden Lee over 1 year ago in reply to Samiha Sharif

Prodigy 30 points

Hi Samiha,

I attached ppt file.

Thanks.

adc_question.pptx

0 Samiha Sharif over 1 year ago in reply to Aiden Lee

TI__Expert 8615 points

Hi Aiden,

Thanks for sharing the schematic. A few points:

Is this problem showing up for both ADCs?
Which ADC is the scope shots taken from?
1. Could you please share an easier to read scope shot? It would help if the time scale was smaller so I could distinguish the SDA and SCL bits.
2. What I2C mode are you using? Hs-mode, standard, or fast mode bus configuration?
The SDA noise looks like it could be bus contention.
1. Are both addresses truly different? Any other same address devices on the bus?
2. Could you try disconnecting the top ADC and see if the bottom ADC SDA line functions properly?

Best,

Samiha

0 Aiden Lee over 1 year ago in reply to Samiha Sharif

Prodigy 30 points

Hi Samiha,

This issue is a hardware issue.

And I resolved this issue.

Thank you for your help.

0 Tom Hendrick over 1 year ago in reply to Aiden Lee

TI__Guru**** 180751 points

Hi Aiden,

Can you let us know what you found? It might be useful to others in the future!

+1 Aiden Lee over 1 year ago in reply to Tom Hendrick

Prodigy 30 points

Hi Tom,

For your information, this issue is hardware issue and not ADC issue.

I use level shifter(TCA9517DGKRQ1) between ADC and FPGA.

However I connected the VCCA with a higher voltage than the VCCB.

So the above problem occured.

I changed the VCCB(5V) to a higher voltage than the VCCA(3.3V) and solved the problem.

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ADC121C021: ADC121C021