DAC80508: Overshoot or Peaking observed in Waveform outputs of DAC

Vijetha HN

Part Number: DAC80508

Hi We are using DAC80508 in our design. We are seeing an over shoot or peaking at leading edge while generating waveforms. This is irrespective of loads (we isolated loads and checked, we see peaking at that condition too).
We see the peaking consistantly from 0V to 4V. Beyond 4V, this peaking disappears. Also the peaking is seen only in the first pulse of waveform sequence.

If we introduce offset to the waveforms then the peaking disapperas.

This observation is seen in all channels of the DAC. This is not accepted for our requirement. So we would like to know reason for this behaviour of DAC. Is this expected from DAC or do you think there is some other reasons for this observation.
Also suggest any changes needed in the circuit.

The schematics of DAC is attached here. The waveform of peaking observed is also shown here.

over 2 years ago

0 Anbu Mani over 2 years ago

TI__Expert 4100 points

Hi Vijetha HN,

Could you please share following information to understand issue better

1. What type of waveform generating ? frequency and amplitude?

2. explain scope plot condition ? Driving voltage amplitude, frequency

Regards

Anbu M

0 Vijetha HN over 2 years ago in reply to Anbu Mani

Intellectual 610 points

1. Square waveform with Frequency : 5KHz, Amplitude : 0.625V, 1V, 4V.

2. I did not get what you are asking.

Here the point is simple : We are generating 5KHz Square waveform ay 0.625V, 1V and 4V amplitude. The raising edge of first pulse exhibits a peaking. Next pulses do not show any peaking. Also if you introduce an offset, then also peaking not observed. Question is why this peak is seen for every first pulse when it makes a transition from 0V.

I hope I provided you enough details to understand our issue and provide a suitable solution.

0 Anbu Mani over 2 years ago in reply to Vijetha HN

TI__Expert 4100 points

Hi ,

1. Understood the problem, could you please share you code sequence. Do you see enough time after SPI configuration before firing square wave ?

2. Output is measured at TP50 ? It is open circuit or connected some other circuit?

0 Vijetha HN over 2 years ago in reply to Anbu Mani

Intellectual 610 points

1. I need to check ith Software team for code sequence and SPI timing.

2. The 7 OUTPUTs are connected to 7 different circuits (amplifiers, buffers etc) for differemt requirements. When we probed at all those 7 channels, we isolated those circuits from DAC output and checked. OUTPUT0 is not used for any purpose and hence we did not check at TP50.

0 Anbu Mani over 2 years ago in reply to Vijetha HN

TI__Expert 4100 points

OK, will see code sequence and SPi timing for any violation.

0 Vijetha HN over 2 years ago in reply to Anbu Mani

Intellectual 610 points

DO you see any issue with schematics?

Also Do you think this is an expected behaviour of DAC part?

0 Anbu Mani over 2 years ago in reply to Vijetha HN

TI__Expert 4100 points

1. Schematic seems good.

2. I think not enough timing before initiate toggling DAC. can you please give some delay (10ms)before firing (toggling) code and check peaking happening on 1st pulse?

0 Vijetha HN over 2 years ago in reply to Anbu Mani

Intellectual 610 points

Hi ANbu,

I checked with SW team about your concern.

SPI is configured at boot time and square wave generation is started when the user selects the sequence generation.There is enough time given to DAC (in seconds) before firing code .