TMS320F280049C: Abnormalities of ADC sampling spike

Katherine Wang

Hi Team,

I have encountered some problems when using ADC.

The figure below shows the waveform of the measurement, where Iout refers to the output current, obc_curr_adc is the signal entering the DSP, and DAC_obc_curr_adc is the value directly converted from the obc_curr_adc pin, which is generated by the DAC, and the DAC output interval time, the same as the ADC value, stands at 50us(20kHz).

It can be observed that the DAC output maintains a spike at an interval, but at the same time the signal entering the DSP does not achieve a spike. When testing other ADC pins, the same situation exists. I would like to know what may have caused the problem, thank you.

Kind regards,

Katherine

over 3 years ago

0 Santosh Jha over 3 years ago

TI__Guru 50611 points

Hi Katherine,

The subject matter expert is out of office due to holiday break. We will get back to you in 1st week of January. Sincere apology for inconvenience.

Regards, Santosh

0 Joseph Casuga over 3 years ago in reply to Santosh Jha

TI__Mastermind 43070 points

Hi Katherine,

What is the width of the spike in DAC_obc_curr_adc? I cannot tell it from the picture due to resolution. Also, can you let me know the SH (ACQPS) of obc_curr_adc? It would also help to see the schematics showing here the DAC output goes and biases the adc network to derive the currents with the resistors/dividers/input caps.

Thanks,

Joseph

0 Katherine Wang over 3 years ago

TI__Intellectual 2210 points

Hi Joseph,

The spike width is 50us, because the value is updated through a 50us interrupt. In addition, ACQPS is set to 100 cycles. thanks.

Regards,

Katherine

0 Joseph Casuga over 3 years ago in reply to Katherine Wang

TI__Mastermind 43070 points

Hi Katherine,

ACQPS of 100 is around 1uS of sampling time if SYSCLK is set at the maximum operating frequency of 100MHz. This should be sufficient to sample a 50uS signal. Can you share the schematics that shows how the DAC is biasing the obc_curr_adc pin, along with any resistor dividers and input/filter caps and values?

Thanks,

Joseph

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TMS320F280049C: Abnormalities of ADC sampling spike