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Dac - 16 bit; 0-5V ; DAC8568

VT
Genius 3300 points
Other Parts Discussed in Thread: DAC8568, OPA703, OPA333

I am looking for 16 bit dac & 16 channel with 0-5V.
Also application is battery powered, so I need DAC to put in sleep when not required.

I had found this octal dac;low power DAC8568 with SPI interface.

Its 8 channel so I need to use two dacs in parallel. But I didn't find CS pin there.
Is there any other alternative to use 2 dacs in parallel . I have only one SPI in my MCU.

  • 0
    TI__Mastermind 46290 points
    Vindhyachal,

    I think the DAC8568 is your best option for this. There is not CS pin in the interface, but the SYNC pin behaves in much the same way.

    Using your single SPI interface, you would connect the CLK and MOSI lines appropriately and use two GPIO pins to connect to each DAC8568 SYNC pin. Use the SPI interface to write the 32-bit frame to the device, then pull the SYNC pin connected to the device of interest low in order to latch the 32-bit data while keeping the other SYNC pin on the other device high.

    Please let me know if you have questions.
  • 0 in reply to Kevin Duke
    Genius 3300 points

    Dear Kevin,

    I have selected DAC8568C, since I need 0-5V output with 0V on power up.

    I have queries (attached is the schematic using two DAC with single SPI.) (applicaiton is battery powered so power is issue)

    1. I don't need LDAC pin. That I will handle in software. I had grounded it directly, or I should pull down with 10K?

    2. Similarly CLR pin is not reuqired. Pin is pulled up with 10K. Should I connect 0.1uF decouple cap here?

    3. Do you have any sample code available for interfacing with MCU over SPI?

    4. I need to put  buffer opamp at output. Which one will be best?

    I am looking for opa333 or opa703. opa333 has very low offset & low power consumption but lesser output drive while opa703 have higher output drive.

    Or you can suggest other opmap.

    7522.ckt.pdf

  • 0 in reply to VT
    TI__Mastermind 46290 points
    Hello,

    1) Tie to GND directly is okay.
    2) No need for extra decoupling capacitor.
    3) I do not believe so, but I will double-check and update this thread if I find something. Are you looking for a flow-chart or code to initialize a specific SPI peripheral?
    4) Can you elaborate on your requirements for this buffer?
  • 0 in reply to Kevin Duke
    Genius 3300 points
    1. Since I have to interface it with MCU so I was thinking of some sample code in C would have helped.
    2. I have to drive a current control circuit(plus additional functionality) which need to be controlled by dac output.
    I don't want to overload dac in any case. So I am thinking of opamp as buffer in between.
  • 0 in reply to VT
    TI__Genius 10615 points
    Hi Vindhyachal,

    Kevin is out of office today attending a work event.

    2) I think we might need some more detailed info on your requirements for the buffer. What is the load of the input of the current control circuit? Do you have an error budget that you are trying to stay under?
  • 0 in reply to Eugenio Mejia
    Genius 3300 points
    I have to give +10mA max at output.
    I have to give full 0 to 5V at output.
    I will operate my circuit from 0-5V. So I have to select some rail to rail opamp for this purpose.
  • 0 in reply to VT
    TI__Genius 10615 points

    Vindhyachal Takniki said:
    I have to give +10mA max at output.

    Out of these two amplifiers, I would recommend using the OPA703. The OPA333 has very low output voltage swing at high output currents. The OPA703 has better swing performance at high output current, but even then voltage drop will be around 1 V.

    This means that if you are sourcing 10mA, you will get ~4 V when you are expecting 5 V. You can see this on page 7 of the OPA703 datasheet.

    I could not find a low-power DAC that had better output voltage swing performance at 10 mA. Maybe you would have a better chance posting this question in the amplifier forum.

    Vindhyachal Takniki said:
    I will operate my circuit from 0-5V. So I have to select some rail to rail opamp for this purpose.

    Keep in mind that even when amplifiers are called "rail-to-rail" they can't quite reach the rail even when unloaded. The best amplifiers will get ~80 mV from the rail.

  • 0 in reply to Eugenio Mejia
    Genius 3300 points
    Thanks for reply.

    I will post the opamp query in amplifier forum.

    1. Will the dac output wll be able to touch rails. Like if I set 0V or 5V full.
    I have read that full scale error = +-0.2% of fsr.

    2. As I had earlier asked, any sample codes with interfacing MCU?