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DAC80501: DAC80501 SPI communication Query

chandrashekhar challur
Prodigy 10 points
Part Number: DAC80501


Dear TI Team,

I am raising this query regarding the the SPI communication of DAC80501 part.

In our application, we have connected cs(Chip select) pin to DAC and shift register parally. I want to  Send 40 bit data frame with 40 clock cycle contneoulsy without any gap.  So that 24 bit(MSB) will be send to DAC and 16bit(LSB) will be send to shif register. 

we thought that DAC will accept first 24 bit (MSB), ( 8 bit commond + 16 bit data) and convert to digital to analog,  The other 16 bit (LSB) will be not be accepted by DAC. 

but when we are sending the 40 bit frame, the digital to analog conversion is not happening. if we try with 24 bit, the conversion is working fine.

In data sheet also, there is no information on what will happen if more than 24 bit frame sent.

could you please clarify, is it mandorty to send 24 bit frame  to DAC always ? or will it work for more than 24 of bits also. (Accept 1st 24 bit(MSB) and igonore remaining bits)

Attached tha waveform for your reference.  (wave form from Evaluation board DAC80502-01 EVM)

Your  quick response will be appcriatated. Thank you.

 image_24_Bit_Frame.pngimage_40_bit_Frame.png

 

  • 0
    TI__Guru 54703 points

    Hi Chandrashekhar,

    The SPI interface is only expecting 24-bits.  Now, it might be possible that the DAC can latch only the last 24bits  of a 40 bit frame.  I dont have the EVM handy to confirm, but you could try sending 16+24bits and see if that works.  The DAC8050x family was never designed with daisy-chain support, so your use-case might not be supportable.

    Thanks,

    Paul

  • 0 in reply to Paul_Frost
    Prodigy 10 points

    Hi Paul,

    Thanks for your reply.

    We tried on the EVM by sending the 40 bit frame. where 16 bit (MSB) dummy data + 24 bit (LSB) (8 bit command and 16 bit data). we got the expected output voltage.

    Now we are working on the our application board by changing the HW circuit.  hence  i would like to keep this ticket open. if we face any issue in our application board, then here we will post it.

    Thanks,

    Chandrashekhar.