TMS320F28335 ADC: Digital vs Analog Supplies

Yes. Hence, use ferrit beads and decoupling capacitors for the analog supply pins.

Best regards,
Edwin Krasser

I've seen the ferrite/capacitor setup on the controlCARD development kits.

Is there a document describing this type of layout for the F28335 chips?

Hi,

I suggest to use ferrit beads and capacitors as in the reference design (e.g. control card).

And about layout, four layers with ground and power (3.3V and 1.9V) plane, all parts on top side, we never had problems. Of course, place the decoupling capacitors as close as possible. But that's obvious.

Best regards,
Edwin Krasser

pls don't waste too much time on C2000 on-chip ADC. sometimes its evaluation board even gives bad results, with or without ferrite beads.

if you need any predictable behavior of ADC, use off-chip ADC. make your layout wires as clean as possible. DGND apart from AGND,

DVDD away from AVDD, digital wires far away from analog input. that's all.

Analog power supply is also 3.3v supply. If you analog supply is noisy it could cause erroneous results.

-Manoj

Yu Cai62050 said:

pls don't waste too much time on C2000 on-chip ADC. sometimes its evaluation board even gives bad results, with or without ferrite beads.

if you need any predictable behavior of ADC, use off-chip ADC. make your layout wires as clean as possible. DGND apart from AGND,

The choice to use the on chip ADC was made for reasons of simplicity and cost. It's too late to change it for this design, but now that we know there can be issues, an off-chip ADC is definitely going to be considered.

Rowan,

Were you able to resolve this issue?  If not, your local TI sales office may be able to provide you with direct support.

-Tommy