The device is designed to operate from a wide input supply voltage range . The input supply must be capable of delivering the required input supply current to the fully loaded regulator over the wide input voltage range. Estimate the average input supply current using Equation 46.

If the regulator is connected to an input supply through long wires or PCB traces with a large impedance, take special care to achieve stable performance. The parasitic inductance and resistance of the input cables can have an adverse affect on converter operation. The parasitic inductance in combination with the low-ESR ceramic input capacitors form an underdamped resonant circuit. This circuit can cause overvoltage transients at the regulator input each time the input supply is cycled ON and OFF. The parasitic resistance causes the input supply voltage to dip during a load transient. The best way to solve such issues is to reduce the distance from the input supply to the regulator and use an aluminum or tantalum input capacitor in parallel with the ceramics. The moderate ESR of the electrolytic capacitors helps damp the input resonant circuit and reduce any voltage overshoots.

An EMI input filter is often used in front of the regulator that, unless carefully designed, can lead to instability as well as some of the effects mentioned above. The AN-2162 Simple Success With Conducted EMI From DCDC Converters application note provides helpful suggestions when designing an input filter for any switching regulator.