8.2.2.4 Input Capacitors

The LM76002/LM76003 device requires an input decoupling and, depending on the application, a bulk input capacitor. The typical recommended value for the high frequency decoupling capacitor is 10 μF to 22 μF. TI recommends a high-quality ceramic type X5R or X7R with sufficiency voltage rating. The voltage rating must be greater than the maximum input voltage. To compensate the derating of ceramic capacitors, a voltage rating of twice the maximum input voltage is recommended. Additionally, some bulk capacitance can be required, especially if the LM76002/LM76003 circuit is not located within approximately 5 cm from the input voltage source. This capacitor is used to provide damping to the voltage spiking due to the lead inductance of the cable. The optimum value for this capacitor is four times the ceramic input capacitance with ESR close to the characteristic impedance of the LC filter formed by the application input inductance and ceramic input capacitors.

For this design, two 4.7-μF, X7R dielectric capacitors rated for 100 V are used for the input decoupling capacitance. A single capacitor has equivalent series resistance (ESR) of approximately 3 mΩ, and an RMS current rating of 3 A. Include a capacitor with a value of 47 nF for high-frequency filtering and place it as close as possible to the device pins.