QPNA4U25F-G/PNA4U25F, QPO-1L, QPO-1LZ

The QPO-1 is an active power filter that provides attenuation of power supply output PARD. The measured attenuation performance over frequency is shown in Figure 3 at output voltage conditions of 3.3 and 28 Vdc. The user can select and optimize the attenuation versus power dissipation by setting the headroom voltage of the active loop.

The conditions in Figure 3 were measured with a low current headroom setting of 375mV with approximately 100mV peak-to-peak ripple voltage on the input to the QPO-1. The remote sense circuit configuration was used as shown in Figure 1 with the peak detector function enabled. Some power supplies need to sense the output ripple for proper operation. Cps couples the unfiltered ripple back to the sense input while Rps provides the DC feedback to the power supply from the load.

Typical improvement in output noise and transient performance with a 3.3V converter is shown in Figure 4. This measured data demonstrates the reduction in noise and ripple at the output of the QPO-1 versus the source output as well as the transient capability stepping from 1 to 10A load current - the maximum current rating. This particular converter has sufficient output capacitance and response time to load changes such that no additional capacitance,CIN, is needed on the input of the QPO-1 to reach a 10A level and still maintain the output within ±50mV.