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AD9280 REFTF/REFBF

Anonymous
Anonymous

Hi,

I am using AD9280 device in my design. I have a question about the voltages I am seeing on REFTF and REFBF pins. I am using this device in external ref mode - 1Vp-p Input span as per Figure 21 on page 12 in the device datasheet. Connections to the device are listed below:

AVDD/REFSENSE/MODE tied to 5V

DRVDD powered from separate 3V3 supply

REFTS connected to external 1V ref

VREF, CLAMP, CLAMPIN, OTR are no connect

REFTF and REFBF are connected as per figure 21

STBY, DRVSS, AVSS are connected to ground

when I turn the supply on I read 3V on REFTF and 2V on REFBF. What values should I see on these pins? Can someone point me on how can I calculate this. Is "A2" in figure 1 an OP-AMP? If it's just a buffer then should I not see the same voltage as REFTS and REFBS respectively?? Thanks.