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AD9705 is not work properly

I’m using AD9705 with AVDD=3.3V, CLKVDD=3.3V and DVDD=3.3V power supply according to data sheet. The DAC_CLK and DB0~9 is controled by FPGA.

In my project, the DAC_CLK is 16Mhz, and IOUTA is connect to 400Ω resister to GND, IOUTB is connect to 400Ω resister to GND. whatever the DB0~9 data is,the voltage of the two 400Ω register is 3.3V。 It looks like AD9705 is not work.

May I ask what's going on here?

Regards.

hcl.

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  • Hello:

    I think you need to change how the OTCM (pin19) is being driven. As stated on page 35 of the datasheet.:

    "The OTCM pin demands dynamically changing current and should be driven by a low source impedance to prevent a common-mode signal from appearing on the DAC outputs."

    I don't think a 4.7k ohm resistor meets that definition of a low source impedance. Try shorting pin 19 directly to ground with a 0 ohm resistor.

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  • Hello:

    I think you need to change how the OTCM (pin19) is being driven. As stated on page 35 of the datasheet.:

    "The OTCM pin demands dynamically changing current and should be driven by a low source impedance to prevent a common-mode signal from appearing on the DAC outputs."

    I don't think a 4.7k ohm resistor meets that definition of a low source impedance. Try shorting pin 19 directly to ground with a 0 ohm resistor.

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