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DAC8775: SPI interface, Power Supply

Sushant Patil25
Prodigy 205 points
Part Number: DAC8775
Other Parts Discussed in Thread: , DAC8760

I have some questions about DAC8775

1. Is is possible to control full functionality of DAC8775 with 4-wire SPI interface(SCLK, SDIN, SDO, SYNC\) ? or  LDAC\, CLR, RESET\, ALARM\ signals also should be connected to controller ?

2. In DAC8775EVM schematic, IOUT_x and VOUT_x are combined and VSENSEP_x, CCOMP_x are connected to this pins. (please check the DAC8775EVM board schematic). I want to use VOUT_x and IOUT_x separately (as a separate channels). kindly let me know the connection for  VSENSEP_x, CCOMP_x and protection circuit for IOUT_x AND VOUT_x.

3. In DAC8775EVM schematic Input supply voltage is converted to fixed 12V and given to DAC8775 (AVDD/PVDD) chip. Is it possible to connect directly 28V DC to DAC8775 (AVDD/PVDD) without much changes in power dissipation and performance.

  • 0
    Prodigy 205 points
    waiting for response.........
  • 0
    TI__Genius 11750 points

    Hello Sushant,

    Please find the information below:

    Is is possible to control full functionality of DAC8775 with 4-wire SPI interface(SCLK, SDIN, SDO, SYNC\) ? or  LDAC\, CLR, RESET\, ALARM\ signals also should be connected to controller ?

    MS: Leaving other digital inputs floating (High-Z) is not recommended, as this would put them in an unknown state, allowing any environmental noise to couple to the pin and may create unwanted transitions on these pin states.

    In DAC8775EVM schematic, IOUT_x and VOUT_x are combined and VSENSEP_x, CCOMP_x are connected to this pins. (please check the DAC8775EVM board schematic). I want to use VOUT_x and IOUT_x separately (as a separate channels). kindly let me know the connection for  VSENSEP_x, CCOMP_x and protection circuit for IOUT_x AND VOUT_x.

    MS: This information closely resembles the information given on page 18 of the DAC8760 design in the link below:

    www.ti.com/.../sbau229.pdf

    In DAC8775EVM schematic Input supply voltage is converted to fixed 12V and given to DAC8775 (AVDD/PVDD) chip. Is it possible to connect directly 28V DC to DAC8775 (AVDD/PVDD) without much changes in power dissipation and performance.

    MS: It is very possible to power AVDD/PVDD directly from a 28V supply. The device can operate with a single external power supply of 12V to 36V when using the integrated buck/boost converters. Most of the data involving device performance versus power supply value can be seen on page 17 and page 25 of the DAC8775 datasheet. Additionally, the schematic included in the datasheet features an application circuit from TIPD (TI Design) 215. The datasheet also reveals that a 12V supply produces better results, in terms of efficiency and power disspation, than other supply values.

    Please let me know if you have any other questions.

    Best Regards,

    Matt

  • 0 in reply to Matthew Sauceda
    Prodigy 205 points
    Hi Matt,

    1. In our schematic we have connected 4 SPI lines to controller and other signals are as follow,
    LDAC\ is pulled down to ground, RESET\ and ALARM\ is pulled up to DVDD, CLR is pulled down to ground and also pull up to DVDD provision has been provided.

    With this we can control full functionality of DAC8775?

    2. And one more point not clear from datasheet is, how much current it will consume on PVDD and AVDD rail when internal buck boost converters are enabled?

    Kindly share me your contact mail id so i can forward the schematic.

    Thanks & Regards
    Sushant
  • 0 in reply to Sushant Patil25
    TI__Genius 11750 points

    Howdy Sushant,

    Please find the answers to your questions below:

    1. LDAC\ is pulled down to ground, RESET\ and ALARM\ is pulled up to DVDD, CLR is pulled down to ground and also pull up to DVDD provision has been provided.

    MS: This sounds mostly correct to me, however, I'll examine your schematic in detail when I receive the PDF through email.  One thing to note is that after power up it is required that a hardware reset is issued using the RESET pin -- this information is listed on page 5 and on page 39 of the datasheet.  Since this is required for correct device operation, you may need to include a general purpose I/O on the RESET pin that is responsible for this toggling the pin.  

    2. And one more point not clear from datasheet is, how much current it will consume on PVDD and AVDD rail when internal buck boost converters are enabled?

    MS: This information is included in page 11 of the datasheet, listed under Power Requirements.  Additionally, there are several graphs which illustrate the relationship between Power Supply Current with Digital Input Code, Temperature, Power Supply Voltages.  These are listed in graphs from page 18-33.

    3.Kindly share me your contact mail id so i can forward the schematic

    MS: I've recently sent you a friend invite, and have shared my email address through an e2e message.