I am using 3 AD9910 to synthesize RF. I am facing a strange throuble, the current output does not exceed 5mA, against the typical 20 mA expected from datasheet. The measures have been done on an impedance of 50 Ohm, which corrispond to the charge that the DDS will load.
I am not using the evaluation board. In the developped home-made board pin 84 (DAC_RSET) is grounded through a 10 KOhm resistance. This fact should allow to reach the "DAC full-scale reference current". OSK is disabled, and I write the Amplitude Scale Factor in single tone prorfile register to modulate the amplitude. I do not write register 0x09, bacause it shouldn't care.
Since the 3 DDSs work simultaneously, and are power up with the same power supply, I tested if the power supply was under dimensioned by setting in sleeping mode 2 of the 3 DDS, but output current of the remaining DDS didn't change.
The AD9910 is used in single Tone mode, is controlled via serial I/O, and is apparently working properly because amplitude and frequency modulations occur when I change the single tone profile contentes.
Would you suggest me some test to do? Or there is any control tha I am not setting?
Thanks in advance