TMS320F28377S: TMS320F28377S

Hi Vadim,

The minimum VREFHI value for TMS320F2837x family of devices is 2.4V. It is not advisable to have a VREFHI setting that is lower than this minimum specified value. If you are sampling a signal that is between 1 to 2V, you can still do that with a typical VREFHI of 2.5V. I'm stating 2.5V as this reference voltage is more commonly supported. You can sample this signal on one of the ADCs.

If you can describe what signal you are trying to measure and how many of these signals you are trying to sample, maybe I can help guide you on how to get started.

Regards,
Joseph

Hi Joseph,
This is an audio signal with max p-p around 1 V. I was looking into several options but it seems the reference scaling is the most economical with good resolution.
thanks vadim

Hi Vadim,

With 1V p-p and signal not going over 2V, best VREF to use is 2.5V. Using 12-bit mode, resolution would be ~610uV and you can sample the audio signal at a maximum rate of 3.5MSPS. For the 1V p-p signal that you are measuring, you will have about 1638 discrete values. Not sure if this is sufficient for your application. However, since you are using LAUNCHXL-F28377S, the on-board reference is set at 3.0V and step resolution will be ~732uV and this will reduce the discrete points to 1365 for the 1V p-p signal.

If your application requires better resolution, you can switch to 16-bit mode ADC conversion. This would improve the resolution to ~46uV per step and you can produce about 21,845 discrete samples for the 1V p-p signal. This would reduce sampling rate to 1.1MSPS though. One caveat in switching to 16-bit mode is that you would have to add an external amplifier for the audio signal that converts the single-ended source (which I assume is what you have) to a differential pair as the TMS320F283xx device family requires a differential input for the 16-bit ADC mode (for improved noise cancelling). If you choose this option though and are OK to use an external amp, you can manipulate amplifier's offset and gain so that the output will be centered around 1.5V with allowance of around 3V p-p. You can then take advantage of the full range of the ADC and further improving the number of discrete point you can convert (close to 65536 points, but you would have to limit the gain to avoid clipping).

You did not indicate how many audio channels you will be sampling but the TMS320F28377S device should have multiple ADC channels and modules that can be used to sample as single-ended or differential.

Lastly, depending on the ADC mode or reference chosen, the factory trims would be applied properly as long as the function AdcSetMode is used. Use of this function is available as part of the ControlSUITE / C2000Ware examples.

Let me know if you have other concerns with your application.

Best regards,
Joseph

Thanks Joseph,

Can 
Can I set  a low reference to some value different from gnd to have a better resolution of the range?

thanks vadim

Hi Vadim,

We did a limited characterization with elevated VREFLO and found that at around 300-400mV, the SNR meets spec but starts to degrade beyond 400mV of VREFLO. It is possible to set VREFLO up to 400mV but you still have to maintain a minimum VREFHI - VREFLO difference of 2.4V as per spec. Having an offset to VREFLO would still not improve resolution in this case.

Best regards,
Joseph