SNVSBZ3 June 2021 LM5168-Q1
The LM516x-Q1 "F" version is designed for fly-buck applications by operating in FPWM mode. Figure 9-1 shows the schematic for a 10-V output fly-buck regulator with a 10-V auxiliary output, capable of delivering 300 mA from each output, used as an example application. Note that the secondary output ground can be floating with respect to the input supply ground. See Table 9-1 for a description of fly-buck terminology used in the this example.
|VOUT1||Primary output voltage, as for a buck regulator. This output is tightly regulated by the LM516x-Q1.|
|VOUT2||Secondary output voltage from couple inductor secondary winding. This voltage is not tightly regulated, but depends on parasitic voltage drops on the primary and secondary sides.|
|IOUT1||Primary output current, as for a buck regulator|
|IOUT2||Secondary output current from coupled inductor secondary winding|
In this data sheet, the effective value of capacitance is defined as the actual capacitance under D.C. bias and temperature, not the rated or nameplate values. Use high-quality, low ESR, ceramic capacitors with an X5R or better dielectric throughout. All high value ceramic capacitors have a large voltage coefficient in addition to normal tolerances and temperature effects. Under D.C. bias, the capacitance drops considerably. Large case sizes and higher voltage ratings are better in this regard. To help mitigate these effects, multiple capacitors can be used in parallel to bring the minimum effective capacitance up to the required value. This can also ease the RMS current requirements on a single capacitor. A careful study of bias and temperature variation of any capacitor bank must be made to ensure that the minimum value of effective capacitance is provided.