Hello,
I want to adjust VREFHIGH for a design which uses F28M35H52C.
In "Hardware Design Guidelines for TMS320F28xx and TMS320F28xxx DSCs " it is mentioned that "The F280x ADC accepts 2.048 V, 1.5 V, or 1.024 V on the ADCREFIN pin." However, in conceto ControlCard design 3.3 V is used as VREF. I will appreciate if some one helps me to find out the correct value for VREFHIGH.
Thanks in advance.
The hardware design guidelines have not been updated to include new ADC architectures. The ADCREFIN levels mentioned in the guidelines apply to (older) devices with one ADC architecture such as the F2812x, F2808x, and F2833x. Even though there aren't electrical specs for the ADC yet in the Concerto datasheet, the architecture is similar to Piccolo series devies (e.g. F2803x) so you can get some information from the Piccolo documentation.
From the Piccolo ADC datasheet electrical specifications below, you can see that there is a range of values you can set for VREFHI. This ADC architecture will scale the conversion range with VREFHI, so if you want conversions to correspond to 0 to 3.3V, you should set VREFHI to 3.3V. You could also achieve conversions corresponding to 0 to 3V by setting VREFHI to 3V.
The ADC also has an internal reference, so you are not required to use VREFHI at all (although you still need to connect the pin on your PCB, probably to VDDA). The internal reference will always give a conversion range of 0 to 3.3V. There are some performance tradeoffs when using internal vs. external reference (internal has potentially higher gain error) so take a look at the Piccolo datasheet to get an idea of the performance.
Hello,
Whats about the internal reference 3.3V if the voltage supply VDDA falls below 3.3V ?
Why VREFLO input voltage is mentioned in the datasheet ? In the datasheet on Page 83 VREFLO = VSSA so VREFLO is always 0V !?
Thanks in advance.
Best Regards,
Jo
