ADS54J60: Differential input full-scale

Maurício Ferreira

Part Number: ADS54J60

Hello,

I'm collecting data with the ADS54J60EVM and TSW14J56EVM with the automation DLL so that I can post-process the data in MATLAB. I need to convert the raw ADC codes to voltage levels. Here's the code I am using:

fid = fopen(filename,'r');
data = fread(fid, 'uint16');
fclose(fid);
N = 16;
FRS = 1.9;
x = FRS.*(data-2^(N-1))/2^N;

where N is the number of bits and FRS the differential input full-scale voltage. This appears to convert the data correctly, but the scaling is slightly different from what can be seen in the HSDC Pro GUI. This discrepancy appears to be eliminated if I use FRS = 2 V. Am I doing this conversion correctly/did I misunderstood the Datasheet?

Regards

over 5 years ago

0 jim s over 5 years ago

TI__Guru* 91947 points

User,

What is your analog input frequency? The digital output values will be slightly off as the frequency increases. See figure 37 of the data sheet.

Regards,

Jim

0 Maurício Ferreira over 5 years ago in reply to jim s

Prodigy 150 points

Hi Jim,

I'm using a 20MHz sine wave as a test signal. My problem is that the voltage levels (as calculated with the given code) only match those observed through the HSDC GUI when FRS = 2. Shouldn't this be 1.9V in this case?

0 jim s over 5 years ago in reply to Maurício Ferreira

TI__Guru* 91947 points

It should be for 1.9V case. Are you measuring the voltage at the input pins of the ADC and comparing this to the code output?

0 Maurício Ferreira over 5 years ago in reply to jim s

Prodigy 150 points

Hi Jim,

I am merely trying to replicate the values shown in the HSDC's plot when the option 'Y-scale in Voltage' is selected. Are these values accurate?

0 jim s over 5 years ago in reply to Maurício Ferreira

TI__Guru* 91947 points

Yes there are.

0 jim s over 5 years ago in reply to jim s

TI__Guru* 91947 points

I am getting conflicting answers now from design team and you may be correct. Working from home does not allow me to test this. Can you verify you are getting 1.9V at the pins of the ADC when you see -0.5dB output codes?

0 Maurício Ferreira over 5 years ago in reply to jim s

Prodigy 150 points

I'm not entirely sure of what you mean by a -0.5dB output code. Is this with the 2^16 th bin as a reference? What would be the best way to test this?
I'm sorry if this is rather obvious. I'm not experienced in these matters.

Thank you for your answer.

0 jim s over 5 years ago in reply to Maurício Ferreira

TI__Guru* 91947 points

-0.5db output in codes would be ~ an output code of 62,260. Sorry for the confusion. What output code are you seeing with a 1.9Vp-p input at the pins?