The LM25149 operational input voltage range is from 3.5 V to 42 V. The device is intended for step-down conversions from 12-V, 24-V, and 48-V supply rails. The application circuit in Figure 9-5 shows all the necessary components to implement an LM25149 based wide-V_IN, single-output, step-down regulator using a single supply. The LM25149 uses an internal LDO to provide a 5-V VCC bias rail for the gate drive and control circuits (assuming the input voltage is higher than 5 V with additional voltage margin necessary for the subregulator dropout specification).

In high input voltage applications, take extra care to ensure that the VIN and SW pins do not exceed their absolute maximum voltage rating of 47 V during line or load transient events. Voltage excursions that exceed the applicable voltage specifications can damage the device.

Care should be taken in applications where there are fast transients at VIN that cause the voltage at VIN to suddenly drop more than 2 V below the VOUT setpoint. The LM25149 has an internal ESD diode from the VOUT to the VIN pins that can conduct under such conditions causing the output to discharge. To prevent damage to the internal ESD diode under the said conditions, TI recommends adding a Schottky diode in series with the VIN pin of the LM25149 to prevent reverse current flow from VOUT to VIN.