8.2.2.3 Input Capacitor

An input capacitor is required for stability. The input capacitor should be at least equal to, or greater than, the output capacitor for good load transient performance. At least a 1-µF capacitor has to be connected between the LP5907-Q1 input pin and ground for stable operation over full load current range. Basically, it is acceptable to have more output capacitance than input, as long as the input is at least 1 µF.

The input capacitor must be located a distance of not more than 1 cm from the IN pin and returned to a clean analog ground. Any good quality ceramic, tantalum, or film capacitor may be used at the input.

Important: To ensure stable operation it is essential that good PCB practices are employed to minimize ground impedance and keep input inductance low. If these conditions cannot be met, or if long leads are to be used to connect the battery or other power source to the LP5907-Q1, TI recommends increasing the input capacitor to at least 10 µF. Also, tantalum capacitors can suffer catastrophic failures due to surge current when connected to a low-impedance source of power (like a battery or a very large capacitor). If a tantalum capacitor is used at the input, it must be verified by the manufacturer to have a surge current rating sufficient for the application. The initial tolerance, applied voltage de-rating, and temperature coefficient must all be considered when selecting the input capacitor to ensure the actual capacitance is never less than 0.7 µF over the entire operating range.