SNVA427C January 2010 – December 2021 LMZ12003
Soft-start capacitor: The soft-start capacitor controls the rise time of the output voltage when power is first applied and following the clearing of a fault mode.
Feedback divider: Regulator output voltage is programmed though the selection of the two resistors, RFBT (aka RFB1) and RFB (aka RFB2). A feedforward capacitor (CFF) is located in parallel with the upper feedback divider resistor. This capacitor improves the step response to abrupt changes in load current. For a different output voltage, see Table 6-1 when modifying the board. Resistor values shown will minimize error in output voltage setting.
RON Resistor: The primary function of the RON resistor is to set the on-time interval of the internal control section switching cycle. The secondary function of the RON resistor is to create a nearly constant operating frequency over the input operating voltage range. If the output voltage of the regulator is changed by adjusting the feedback divider, then it is generally required that the RON resistor value also be changed in order to maintain the same operating frequency.
Cout: A parallel connection of a 1-µF, 50-V and a 100-µF, 6.3-V multilayer ceramic are used for the output capacitor. Locations are provided on the PCB assembly for experimenting with additional output capacitors..
Cin: A 10-μF, 50-V multilayer ceramic is connected as the input filter. Locations are provided on the PCB assembly for experimenting with additional input capacitors.