AD9283-100 reference voltage

Hi! 

I am using AD9283-100 operating at 50MHz. Ian using internal reference. I am always getting output code as all zeros. When I monitored the Vref at Pin 2 and Pin 3 shorted to ground I am getting 1.82V instead of specified 1.25V. what could be the reason.

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  • Hi Satish,

    Thanks for the additional info regarding your measurements. Please note the Analog Input Common Mode voltage is internally biased at a value of ~0.3 x VD, or 0.9V when operating from a nominal 3V supply. Please refer to datasheet figure 2 and the Analog Input Theory of operation on datasheet page 8. The Analog Input Common mode voltage is not directly influenced/biased from the fixed internal 1.25V VREF OUT voltage. The 1.25V VREF controls the Analog input full-scale span which by default is 1.024Vp-p.

    You can think of the Analog Input Common Mode Voltage (~0.9V with a 3V supply) as the fixed midpoint with the Ain signal swinging +/-0.512V (1.024Vp-p) around this CM midpoint in single-ended (SE) Mode. For SE mode you will typically drive the AIN terminal with your 1.024Vp-p AC coupled signal, while leaving the AIN/ floating, or preferably connected through a 0.1uF cap and 25ohm series resistor to Ground. I'm attaching an Ain Voltage vs output coding table to help illustrate.

    Please verify your supplies and decoupling nodes are properly configured. I will be happy to contact you offline via your EZone registration email if you would prefer to share your AD9283 schematic/layout outside of the public forum. Just let me know...

    Best Regards,

    TonyM

    8b_AD9283_ADC_Output_Coding.xls
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