Due to the very low forward resistance of the DMOS switching transistors, high current demands are placed upon the input supply for a short time. By using a good-quality low Equivalent Series Resistance (ESR) capacitor of 2.2 μF (minimum) for the 5-V input devices and a 0.47-μF capacitor for the 12-V and 24-V devices, placed close to the IC supply input pins, the effects on the power supply can be minimized.

The high switching frequency of 400 kHz allows relatively small values of capacitors to be used for filtering the rectified output voltage. A good-quality, low-ESR, 1-μF ceramic capacitor placed close to the VREC pin and output ground is required and reduces the ripple. The output at VREC is full wave rectified and produces a ripple of 800 kHz.

TI recommends that a 0.1-μF, low-ESR, ceramic capacitor is connected close to the output pin and ground to reduce noise on the output. The capacitor values listed are minimum values. If lower ripple is required, the filter capacitor must be increased in value to 2.2 μF.

As with all switching power supplies, the best performance is obtained with low-ESR, ceramic capacitors connected close to the device pins. If low-ESR, ceramic capacitors are not used, the ESR generates a voltage drop when the capacitor is supplying the load power. Often a larger capacitor is chosen for this purpose, when a low-ESR, smaller capacitor performs as well.