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TIVA C devices ADC do not have an internal reference?

Prad1
Genius 3825 points
Other Parts Discussed in Thread: TM4C123GH6PM

Hi,

We need some clarifications about the TIVA C ADC reference.

The "System Design Guidelines for Tiva™ C Series" mentiones as below about the internal reference

"Tiva C Series TM4C microcontrollers offer greater ADC precision and require an external reference
voltage. The TM4C circuit should provide a precision voltage source to either the VREF+ or VDDA pin.
The designer should determine whether the internal reference has sufficient accuracy or if an external
reference is needed"

1.Just wanted to clarify that,there is no internal reference for ADC in TIVA C?

In case of devices like "TM4C123GH6PM" which do not have the "VREFA+ and VREFA-" reference input,
I think VDDA and GNDA is the only option for voltage reference.

2.But the VDDA is also the supply for all of the analog circuitry on the device(including the clock circuitry)
which may be affected due to internal voltage drop, so in order to get the precise ADC measurements
what are necessary things have to be considered with VDDA(as the voltage reference)?

Best Regards.
Prad.

  • 0
    Genius 3825 points

    Please let me know if there is any comment on this question.

    Is there any plans to release ADC application note like Stellaris below?
    http://www.ti.com/lit/an/spma028/spma028.pdf

  • 0
    TI__Intellectual 2615 points

    Prad,

    On devices with no VREF pins the VDDA pins will be the reference.

    To ensure a stable VDDA and improve ADC sampling, we recommend adhering to the following guidelines:

    • During normal MCU operation the power supply rail VDDA must remain within the electrical limits listed in the datasheet Vdd(min) and Vdd(max).
    • In most cases VDDA can be connected directly to the power plane that is tied to the VDD pins. Some applications may justify separation of VDDA from VDD to allow insertion of a filter to improve analog performance. If this is the case VDDA can be separated from VDD with either a low-value resistor or inductor/ferrite to form a low-pass filter.
    • Noise sources such as audio transducers, relays and other power-switching circuits should have their own supply rails, especially if ADC performance is a factor.
    • VDDA  should be decoupled with a 0.01uF and 1uF capacitor between VDDA and GNDA close to the TM4C123x  device to provide maximum ADC precision. GNDA should be attached to GND at a single point.
    • VDDA supply rail must power up prior to or simultaneously with the VDD supply rail for proper operation.
    • There is not a maximum VDDA to VDD timing requirement which allows VDDA to be supplied from a separate high precision regulator if desired.

    Hope that helps!

    --Miles

  • 0 in reply to Prad1
    TI__Intellectual 2615 points

    Prad,

    The ADC's are the same in the Tiva parts as in the Stellaris parts.  That AN is applicable to Tiva C as well.

    --Miles