8.2.2.3.1 Output Voltage Setting

A resistor divider network from V_OUT to the FB pin determines the desired output voltage as follows:

Equation 20.

R_fbt is defined based on the voltage loop requirements and R_fbb is then selected for the desired output voltage. Resistors are normally selected as 0.5% or 1% tolerance. Higher accuracy resistors such as 0.1% are also available.

The feedback voltage (at V_OUT = 2.5 V) is accurate to within –2.5% / +2.5% over temperature and over line and load regulation. Additionally, the LMZ10504EXT contains error nulling circuitry to substantially eliminate the feedback voltage variation over temperature as well as the long-term aging effects of the internal amplifiers. In addition the zero nulling circuit dramatically reduces the 1/f noise of the bandgap amplifier and reference. The manifestation of this circuit action is that the duty cycle will have two slightly different but distinct operating points, each evident every other switching cycle.