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DAC9881: DAC9881 Vout does not match SPEC

user5008633
Prodigy 70 points
Part Number: DAC9881

Hi,

Please can any one help me abort  input DAC Code to DAC9881.

I through the SPI transmission DAC code to DAC9881 , but Vout value does not match SPEC.

I confirm all circuit is correct and SPI  format.

How do I do the same with SPEC Vout?

Please help me,thanks.

DAC Code

Ideal value

Measure value

3FFFFH

4.99998V

6mV

30000H

3.75000V

1.251V

20000H

2.50000V

2.503V

10000H

1.25000V

3.755V

00000H

0.00000V

4.747V

Test Condition:

1. AVDD=5V

2. IOVDD=5V

3. VREFH=5V

4. VREFL=GND

5. LDAC=GND

6. SDOSEL=IOVDD=5V

7. RST=5V

8. PDN=GND

9.USB/BTC=IOVDD=5V

10. GAIN=GND

11. RSTSEL=GND

SY

  • 0
    TI__Mastermind 46290 points
    SY,

    It almost looks like there is some shift being applied to the data along with the device somehow being in binary two's complement mode. Could we see an oscilloscope capture of the SPI lines during communication?
  • 0 in reply to Kevin Duke
    Prodigy 70 points

    Hi Kevin,

    Thanks your reply.

    The following SPEC DAC Code corresponds to the SPI format:

    Definition:

    CH4:CS；CH3:SDI；CH2:SCLK

    1. DAC Code=00000h

    2. DAC code=10000h

    3. DAC code=20000h

    4. DAC code=30000h

    5. DAC Code=3FFFFh

    The following is a summary of the measured data:

    DAC Code

    (Straight Binary Code)

    SPEC Vout

    (USB/BTC=IOVDD)

    Measure Vout

    3FFFFH

    4.99998V

    5.6mV

    30000H

    3.75000V

    1.251V

    20000H

    2.50000V

    2.503V

    10000H

    1.25000V

    3.755V

    00000H

    0.00000V

    4.754

    DAC Code

    (Twos Complement Code)

    SPEC Vout

    (USB/BTC=GND)

    Measure Vout

    1FFFFH

    4.99998V

    5.8mV

    10000H

    3.75000V

    1.250V

    00000H

    2.50000V

    2.501V

    3FFFFH

    2.49998V

    2.501V

    30000H

    1.25000V

    3.752V

    20000H

    0.00000V

    4.754V

    Above data reference,

    Please help me again,thanks.

    SY

  • 0 in reply to user5008633
    TI__Genius 14220 points
    Hi SY,

    The waveforms look ok to me. Let me test it out on the EVM myself and get back to you.

    Are you checking this on your hardware or EVM?

    Regards,
    Uttam Sahu
    Applications Engineer, Precision DACs
  • 0 in reply to Uttam Sahu
    Prodigy 70 points

    Hi Uttam,

    Thank you reply,

    I check my hrdware again, I consider my DAC9881 board VREFH-F and VREFH-S .

    I Refer SPEC
    1. www.ti.com/.../dac9881.pdf
    2. www.ti.com/.../slau279a.pdf

    I would be these two pins connect together without OPA(High Precision Dual Operational Amplifier).

    I do not know if there is any impact my Vout. (DAC code input DAC9881 ,output negative Vout from DAC9881)

    Please help me again,thanks.

    SY

  • 0 in reply to user5008633
    TI__Genius 14220 points
    Hi SY,

    Can you try out the DAC9881EVM and see if you see similar behavior?

    Regards,
    Uttam