Frequently Asked Question
If I violate the proper logic level of the REF CLK (that is, underdrive or overdrive it), what can I expect?
If you overdrive the REF CLK input(s), you may forward bias diodes that are present at the input for ESD protection. These diodes terminate to VCC and GND; therefore forward biasing them could dump digital noise on power or GND busses. It is important to maintain a good AC ground at both GND and all power pins.
If you underdrive the REF CLK input(s) you may experience intermittent problems such as glitches on the DAC output; or the part may not respond at all. The presence of a sufficient REF CLK signal on the device can be quickly checked by monitoring the power supply current (digital). If the input REF CLK circuitry is not switching, the total current will be significantly reduced. This is because the DDS consists of mostly CMOS digital circuitry which does not draw much current when not switching.