The RT/SD pin provides ON and OFF control for the LM5008A. When VSD is below approximately 0.7 V, the device is in shutdown mode. Both the internal LDO and the switching regulator are off. The quiescent current in shutdown mode drops to 110 µA (typical) at VIN = 48 V. The LM5008A also employs VCC bias rail undervoltage protection. If the VCC bias supply voltage is below its UV threshold, the regulator stays off.