GDU DC link wrong measurement

[buch2001]

Hi,

I inherited a project and, trying to solve some problems, I found this behavior that I can't explain.

We use the internal channel 3: GDU DC link to measure the supply voltage, but the measurement is always higher than expected.

For example: I measure with the multimeter on the GHD pin 12.5V but the ADC always returns 520bits, which corresponds to 520*5/1024*5=12.69V (bits*full_range/max_bit*divider)

I know that the result is compliant with the divider tolerance (4.9/5.1), but the error is systematic and I have tried different boards and so I don't think is a divider problem..

Is there something I am missing?

Any help is greatly appreciated.

Thanks in advance

Marco

[lama]

Hi,

I would like to share what came into my mind....

incorrect vrh, vrl (vrhsel, vrlsel) + used/unused external PNP which defines reference (Ref. manual Chapter B.1 VREG Electrical Specifications itm 4a,4b, 4c)
incorrect atd clock
not solved unused ATD pins (from AN4867.pdf: ADC unused pins should be grounded to reduce leakage currents.)

Best regards,

Ladislav

[buch2001]

Hi lama,

thank you for your reply.

I have checked and everything seems fine. But anyway, if there was something wrong as you said, I would have errors in any ADC conversion, but in my case only the battery voltage coming from the GDU DC Link has this mismatch.

Thanks again,

Marco