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TMS320F28379D: X-BARs, eCAPs, CMPSS and ADCs

Nikola Djordjevic
Prodigy 220 points

Part Number: TMS320F28379D
Other Parts Discussed in Thread: TL431, OPA320, OPA350

Hello all.

I should use Delfino F28379D, so in the mean time some questions has appeared.

I realized that INPUT X-BAR is essential for using eCAP function (this periphery was independent and phisically availible on Piccolo 28027 and 28035). 

OUTPUT X-BAR is using for output of CMPSS comparators among the others.

Questions:

1) Could I use any six GPIOs for eCAP1 - eCAP6 via INPUT X-BAR simultaneously?

2) Could I use CTRIPOUTxH and CTRIPOUTxL for all of 8 CMPSS outputs via OUTPUT X-BAR simultanously? I saw that there are only OUTPUTXBAR1 - OUTPUTXBAR8, but 16 is needed. I assume that I have not understood something.

3) In my application, I am using almost all ADCs (almost all free ADCs where CMPSS aren't used). Need I provide external VREFHI 3.3V from my custom board because many of ADCs are used? I use ADCs in single-ended mode. Could somebody to clarify in which cases an external VREFHI is using?

Thanks in advance!

Regards,

Nikola.

  • 0
    Prodigy 220 points

    I didn't say that I should use Delfino F28379D Control Card on my custom board and isolated JTAG connection with the PC.

    I will provide 5V power supply on HSEC pins from my board, so the refference 3.3V (VDDA_MCU_3V3) I could get via SW2 and SW3 configuration, and in this case, the reference is provided from the IC_LDO_TPS62420DRC linear voltage regulator from the control card.

    Is this configuration enough for using all of 24 ADCs when it comes to power consumption? Also, does the IC_LDO_TPS62420DRC have enough power when using a lot of peripherals? I read in some datasheet that maximal power consumption of the control card is about 400 mA, but in case where all peripherals are unused, as I understood.

    On the other side, I would provide external 3.3V on HSEC_ADC-VREFHI pin with TL431 (Iout_max = 100mA).

    Is there somebody to advice me about this?

    Regards, Nikola.

  • 0 in reply to Nikola Djordjevic
    TI__Guru 60865 points
    Hi Nikola,

    1) Yes, you can use any GPIOs as eCAP inputs via input X-bar lines 7 through 12
    2) There are only 8 output X-bar paths, so only 8 CMPSS signals will come out directly. If you need more to come out your best bet is to use the CMPSS signals to trip ePWM modules to cause an ePWM pin state toggle. You would need unused ePWM modules for this.
    3) Regardless of how many pins are used on a given ADC, if you use an ADC you need to provide an external reference voltage for it. This voltage will probably be 2.5V or 3.0V instead of 3.3V. Using a shunt reference directly will likely result in poor performance; you will want to drive the reference signal in with a high-bandwidth buffer like OPA350 or OPA320 similar to the design on the CCard and LaunchPad.
  • 0 in reply to Devin Cottier
    Prodigy 220 points

    Hi Devin.

    Thank you on your feedback.

    I know that I need reference voltage voltage for ADCs, but I would use Control Card 28379D. This card has own linear voltage regulator (5V input, 3.3V output). This 3.3V is used for voltage reference IC REF5030IDGKT to generate reference 3.0V on the CCard. With switches SW2 and SW3 I could choose between that 3.0V provided by REF5030IDGKT and VDDA_MCU_3V3 that is also provided on CCard (in the initial case where resistor 0 ohm R60 is populated, and R59 is not populated).

    My input signals to ADCs are 0 to 3.3V, and the resolution 3.3/4096 is ok for me. So I need to have reference 3.3V.

    My question that I am still not clear is:

    Could I use VDDA_MCU_3V3 provided from CCard, or I have to use an external reference (reference provided on my custom board and connected via 0 ohm resistor R59 to HSEC_ADC-VREFHI pin of CCard)? As I could see on the schematic of CCard, in the case of using HSEC_ADC-VREFHI by populating od R59, and DNP R60, output of 3.3V reference from my board will be connected to VREFHIA -VREFHID via OPA350 buffer amplifiers (when SW2 and SW3 are configured correctly).

    My questions was going to the side of power consumption in the case of using almost all ADCs.

    Thanks a lot on your effort to clarify that issue.

  • 0 in reply to Nikola Djordjevic
    TI__Guru 60865 points
    Hi Nikola,

    It is possible to use the VDDA voltage as the VREFHI input, but this will probably result in pretty noisy ADC results since any noise on the VREFHI pin will directly couple to the ADC output.

    Using a precision 3.3V reference is possible, but tricky. The issue is that VREFHI < VDDA must be met at all times (see Table 5-43 ADC Operating Conditions (12-Bit Single-Ended Mode) in the datasheet www.ti.com/.../specifications . Since VDDA is nominally 3.3V it wouldn't be allowed to drift at all in the negative direction. Therefore you would have to set the nominal VDDA voltage somewhere in between 3.3V and the max VDDA voltage of 3.47V such that the negative tolerance in the VDDA supply will always remain above 3.3V.

    ADC current consumption (on VREFHI, VDDA, and VDD) will be maximized with maximum ADC sample rate. The VREFHI average current draw isn't particularly large (~130uA, see Table 5-44 "ADC Characteristics (12-Bit Single-Ended Mode)") but the transient currents are large and need a strong driver and large capacitance to be handled.
  • 0 in reply to Devin Cottier
    Prodigy 220 points

    Hi Devin.

    As I understood, I can't use VDDA 3.3V in combination with external precise 3.3V reference because I use CCard (not the 28379D chip but CCard on HSEC connector on my custom board). VDDA voltage is provided from LDO on the CCard and 3.3V is fixed.

    So, my solutions are:

    1) to use VDDA 3.3V with possible noise problems or

    2) to use internal precise 3.0V, but in that case my input signals to ADCs must be in range 0 - 3.0V.

    Am I write?

    What will happen if some signal at the input of ADC exceed 3.0V in solution No.2?

    Regards, Nikola.

  • 0 in reply to Nikola Djordjevic
    TI__Guru 60865 points

    Hi Nikola,

    Yeah, that is correct.

    In the case of (2)

    • If the input is in the range of [3.0V, VDDA + 0.3V] then the ADC will produce the maximum output code
    • If the input is greater than VDDA + 0.3V, the input will start to clamp to VDDA via internal ESD diodes.  If the total clamping current on all pins (including digital) exceeds 20mA, then the device could be permanently damaged.

    (3) Would be that you supply VDDA with about 3.4V @ 2% tolerance and then use a 3.3V precision reference voltage.  

  • 0 in reply to Devin Cottier
    Prodigy 220 points
    It is now fully clarified!

    Thanks a lot!