AD9106 is not working but I can't figure it out why

Question

I'm trying to configure the AD9106 to generate a sawtooth wave for driving the galvometer I use an Xillinx FPGA to generate the corresponding SPI signals to communicate with the AD9106 However, whatever I changes the settings, the output of the AD9106 remains a 0.01V DC constant. 
 I tried to change the BGDR code of the 0x03 register, the IOREF voltage is changing correspondingly as I expected, which implies that the SPI communication is working, 
 I powered the AD9106 with 2.5V, the LDO pads is 1.8V, which is as I expected, indicating that the chip is not broken( I guess). 
 I suspect that I've done somthing wrong in the output stage circuit 
 The image below is our output stage circuit and AD9106 circuit schematic. 
 The clocking is clocked by a on board LVDS oscillator, directly fed in the CLK_P CLK_N port (which I couldn't measure it on the oscilloscope) 
 I need assistance 
 I appreciate your help very much.

JMMina · Accepted Answer

Hi Evan89523 , 
 There should be an RC filter from IOUT+ and IOUT- going to the amplifier, but the difference I see is that the feedback pin (FB) in your schematic is shorted to OUT. This could be a problem because since your Op-amp supply is &plusmn;12V (output will swing along this range), the output pins will effectively be (299 &Omega;/499&Omega;)(&plusmn;12V) &asymp; &plusmn;4V, which is well above the Abs Max rating for the IOUT pins. Based on your schematic, DVDD is 2.5V. Can you check the voltage readings at the output pins (DAC_OUT1 P/N)? 
 Although, I simulated your circuit in LTSpice and got the waveform below, is this your expected output? I used 5.2V for the supply of the amplifier similar to the evaluation board. 
 
 The resistors connected to P5V2 and N5V2 can be used for configurating the common mode level going to the amplifier. Nominally, the common-mode is 0V based on the resistors (R61, R63) and P5V2 and N5V2, but modifying the resistances provides a different common-mode level. Care must be taken to ensure the DAC output must still be within compliance. 
 Regards, 
 Marco)

Electronic Design Services - PartnerZone

Products In This Thread

AD9106 is not working but I can't figure it out why