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TMS320F280049: PLC with AFE031

Gunter Schmer
Genius 14312 points
Part Number: TMS320F280049
Other Parts Discussed in Thread: AFE031, OPA521

Hi,

a customer was looking at the PLC PHY implementation with the AFE031, where the C2000 device is using precise PWM to generate the fundamental frequencies for FSK based PLC.

http://www.ti.com/lit/an/sprac94c/sprac94c.pdf

The customer was wondering if it is possible with the new F280049 to use the 12-bit buffered DAC which can achieve max 500 ksps, to actually generate the sine waves as inputs to the AFE031. is this possible? 

Thanks!

--Gunter

  • 0
    TI__Mastermind 45606 points

    Hi Gunter,

    Yes, I believe this should be possible. I'll ping someone from the amplifier team to comment on the specifics of their devices.

    You're thinking of using the AFE03x TX path described in the "DAC mode" section of the app note, correct? Just replacing the AFE031's 10 bit DAC with the F28004x's 12-bit DAC?

    There may be an alternative option to use the F28004x's DAC with a Power Amp (such as the OPA521) along with any necessary external filtering circuitry. However this has not been proven out at this time.

    Best,

    Kevin

  • 0 in reply to Kevin Allen18
    TI__Guru* 77541 points

    Hi Gunter,

    C2000 is definitely able to modulate 500kps PWM based Sine wave. And AFE031's transmitter has the BW to handle it, see p.8 of AFE031's datasheet. However, PWMed at 500kbps may not be necessary; and it is going to generate a quite bit harmonics, and the generated sine signals still have to go through LPF before entering programmable Tx  amplifier, then it is sent out via power amplifier. 

    Best,

    Raymond

  • 0 in reply to Raymond Zhang1
    TI__Genius 14312 points

    Hi Kevin and Raymond,

    yes, I was referring to the "DAC mode" section of the appnote, but rather than sending values over SPI and using the internal AFE031 DAC, instead using the F28004x 12-bit DAC. 

    This could then potentially lead to a design with F280049 and discrete OpAmp and Filtering.

    It sounds like you are saying it could be possible, but has not been proven.

    Thanks!

    --Gunter

  • 0 in reply to Gunter Schmer
    TI__Guru* 77541 points

    Hi Gunter, 

    Yes, you can do it. However, you have disable AFE031's internal DAC switch (connected to SPI--> DAC); and you will have to connect and feed MCU's DAC signal to  Tx_PGA_In pin, see the attached image. It has been done among many current customers.  

    If you use the external DAC, then AFE031's internal DAC mode is bypassed completely. This is similar to PWM-mode when it is implemented with AFE031. PWM-mode is a lower cost approach when interfacing with AFE031, because lower speed MCU is required. PWM mode is to add two offset PWM signals in phase, and use LPFs to generate the specific sine transmission frequencies over the power line. 

    Your approach is similar, but with higher resolution DAC to accomplish the same thing.  Of course, we can short out the external unused LPF filters, except with one LPF, which is to minimize the harmonics from PWM generated sine frequencies. 

    Best,

    Raymond