TMS320F28335: ADC Function

Hi,

Is this a custom board? Can you please share your schematic for ADCREFP and ADCREFM? 

Toshimasa Kurakake said:

Vadcrefp-ADCREFP：Specification 1.275V⇒Measurement value 1.4094V
Vadcrefm-ADCREFM：Specification 0.525V⇒Measurement value 0.5977V

Best Regards,

Ben Collier

Hi Ben,

Yes.Custom boards designed by us.
An excerpt of the schematic is attached.

Best Rgards,

Toshimasa Kurakake

Tohsimasa,

Toshimasa Kurakake said:

Vadcrefp-ADCREFP：Specification 1.275V⇒Measurement value 1.4094V
Vadcrefm-ADCREFM：Specification 0.525V⇒Measurement value 0.5977V

When you are using external reference and measuring these values, what voltage do you see at ADCREFIN? 

Thanks,

Ben Collier

Ben,

✕　ADCREFSEL：Specification 2.048V⇒Measurement value 2.048V

〇　ADCREFIN：Specification 2.048V⇒Measurement value 2.0479V

Thank you,

Toshimasa Kurakake

Toshimasa,

Could you also please check the other power pins like VDDA and VDDIO/VDD? 

I'm trying to figure out why REFP and REFM are incorrect. 

Thanks,

Ben Collier

Ben,

VDD    (29)    1.9110V
VSS    (30)    -0.0002V
VDD1A18    (31)    1.7991V
VSS1AGND    (32)    0.0000V
VSSA2    (33)    0.0000V
VDDA2    (34)    3.3286V
ADCLO    (43)    0.0000V
VSSAIO    (44)    0.0000V
VDDAIO    (45)    3.3287V
ADCREFIN    (54)    2.0479V
ADCREFM    (55)    0.5975V
ADCREFP    (56)    1.4094V
ADCRESEXT    (57)    0.8690V
VSS2AGND    (58)    0.0000V
VDD2A18    (59)    1.7984V
P3.3V　　3.3309V
P1.9V　　1.9111V
DGND　　-0.0015V
* ( ) Pin No

Thank you,

Toshimasa Kurakake

Hi,

Do all of your boards have this problem, or is it only one? 

Ben,

All boards have this problem.

Thank you,

Toshimasa Kurakake

Could you try adding a 1uF - 10uF capacitor on the ADCREFIN pin? 

What are using to supply the ADC reference? Can you share that circuit? 

Thanks,

Ben Collier

Hi Ben,

I added a 10uF capacitor to the ADCREFIN pin, no change.

Thank you,

Toshimasa Kurakake

Hi, 

Is there any chance that the PCB manufacturer has made a mistake with the values of the passive components? 

Also, just curious, did you start your development with a control card? 

Thanks,

Ben Collier

Hi Ben,

Which component value would be considered incorrect to cause this phenomenon?

Thank you,

Toshimasa Kurakake

R36, C39, C40, C41? 

Also could you see if there is any effect from shorting L5 and L6? 

Thanks,

Ben Collier

Hello,

I will check by Friday.

Can this happen with register settings?

Thank you,

Toshimasa Kurakake

Toshimasa,

If you are using a TI example, this InitAdc() function will be called as a part of initialization. It is key for loading trims into ADC registers. 

I assumed you have done this if you started with TI software, but please use the InitAdc() function if you are not already. 

Best Regards,

Ben Collier

Hi Ben,

I did not use software samples.
However, I don't see how register settings could cause this problem.
I will check the components you mentioned and will implement a short circuit for L.

Thank you,

Toshimasa Kurakake

Hi,

Please try using the InitAdc() function. It is necessary for loading trims to the ADC. The performance in the datasheet is only guaranteed if you are using the trims programmed to the device during test. The InitAdc() function will do that for you.

Best Regards,

Ben Collier

Hi,

R36, C39, C40, C41? ⇒OK

Also could you see if there is any effect from shorting L5 and L6?⇒ Unchanged

Thank you,

Toshimasa Kurakake

Toshimasa,

Could you try using one of our ADC examples? This will make sure that your trims are loaded correctly.

Thanks,

Ben Collier