Question
I have a new design where I use the AD9117. I am not getting the expectedvoltage swing on the output.
I configure the device via the SPI interface, and change xRSET to 2 kohm.xOUTN is connected to RLxN and xOUTP to RLxP. CMLx is connected to GND. WhenI write the full code rate of 0x0000 to 0x3FFF to the device, then I get anoutput voltage swing of 55 mV to 410 mV. I expected a swing from 0 V to 1 V,as explained in the datasheet.
I’ve confirmed that REFIO has a voltage of 1 V.
What could be the reason why I am not seeing a 1 V swing on the output?
Answer
Setting IRSET and QRSET to 0x80 enables on chip IRCML and QRCML full scalecurrent set resistors. IRSET[5:0] = QRSET[5:0] = 0x00 sets these resistors to4k?. This results in an IOUTFS of 8ma. (See figure 98 in the data sheet). Thecustomer is using 62.5? on chip IOUT and QOUT load resistors and a board level560? resistor for an equivalent load of 56.224? load on each DAC output. Thepeak voltage is IOUTFS x 56.224?. This is 0.45V with their IRSET and QRSETsettings. With IRSET[5:0] = QRSET[5:0] = 0x23 (setting of 35 decimal toachieve 18ma IOUTFS as shown in figure 98) the peak voltage is .018 x 56.224 =1.012V.