Waveform distortion encountered in the output of the AD5543 DAC. How can this signal be improved?
The internal output capacitance of the DAC introduces a pole into the open loop response which can cause ringing or instability in the closed loop ramp profiling circuit. This can be compensated using an external feedback capacitor, C1 , usually connected in parallel with the internal RFB of the DAC. Too small values can produce waveform distortion at the output, while too large values can adversely affect the bandwidth of the system. Since the internal output capacitance of the DAC varies with code, it is difficult to fix a precise value for C1. The value is best approximated according to the equation:
Where GBW is the small signal unity gain bandwidth product of the op-amp in use and CO is the output capacitance of the DAC.