TMS320F28069: The input circuits for analog ADC input channel.

Shuai Yuan

Part Number: TMS320F28069
Other Parts Discussed in Thread: ADS8319

Tool/software:

Hi Team,

My customers want to use TMS320F28069 internal ADC for current signal sampling, however they need to decrease the voltage which is the output from the filter AMP by divided resistors before it connects to the ADC input. Then the input signal voltage range will be falls in the power range of 28069.

Could you please help to show some guidance with the divided resistors value? These values shall not affect the internal input impedance.

Best regards

Shuai

1 month ago

0 Benjamin Collier 1 month ago

TI__Mastermind 21901 points

Hi Shuai,

Shuai Yuan said:
These values shall not affect the internal input impedance.

What do you mean by this? Could you provide a schematic for this ADC input circuit? That might be easier for me to understand.

We have these app notes:

https://www.ti.com/lit/an/spract6/spract6.pdf

https://www.ti.com/lit/an/spracv0/spracv0.pdf

These are targeting newer devices, but the concepts apply to F2806X as well.

Best Regards,

Ben Collier

0 Shuai Yuan 1 month ago in reply to Benjamin Collier

TI__Intellectual 2290 points

Hi Ben Collier,

Below is the block diagram of current sampling circuits, as the power rail of ADS8319 is higher than F2806x, customer wants to use R1 and R2 divided resistors to decrease the voltage range within 3.3V

As there need to impedance balancing, Could you please help recommend the R1 and R2 value level?

Best regards

Shuai

0 Benjamin Collier 1 month ago in reply to Shuai Yuan

TI__Mastermind 21901 points

Hi Shuai,

What is the output voltage of the amplifier?

Best Regards,

Ben Collier

0 Shuai Yuan 1 month ago in reply to Benjamin Collier

TI__Intellectual 2290 points

Hi Ben Collier,

The Max. Voltage of R1 left side is 4.096V

Regards

Shuai

0 Benjamin Collier 1 month ago in reply to Shuai Yuan

TI__Mastermind 21901 points

Shuai,

I would like for the customer to design the circuit themselves, but here is the guidance that I can give:

They should use this page of the first app note that I linked as a reference.

(5.23K Ohm + R1) will be their Rs in the above model. This will affect the time for sample and hold capacitor to charge and thus their maximum sampling rate. There are more details in the app note.

I would also recommend that the customer does a TINA Spice simulation as discussed in the app note.

Best Regards,

Ben Collier

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TMS320F28069: The input circuits for analog ADC input channel.