The LM5002 VCC low dropout (LDO) regulator allows the LM5002 to operate at the lowest possible input voltage. The VCC pin voltage is very nearly equal to the input voltage from 2.8 V up to approximately 6.9 V. As the input voltage continues to increase, the VCC voltage is regulated at the 6.9 V set-point. The total input operating range of the VCC LDO regulator is 3.1 V to 75 V.

The output of the VCC regulator is current limited to 20 mA. During power-up, the VCC regulator supplies current into the required decoupling capacitor (0.47 µF or greater ceramic capacitor) at the VCC pin. When the VCC voltage exceeds the VCC UVLO threshold of 2.8 V and the EN pin is greater than 1.26 V the PWM controller is enabled and switching begins. The controller remains enabled until VCC falls below 2.7 V or the EN pin falls below 1.16 V.

An auxiliary supply voltage can be applied to the VCC pin to reduce the IC power dissipation. If the auxiliary voltage is greater than 6.9 V, the internal regulator essentially shuts-off, and internal power dissipation is decreased by the VIN voltage times the operating current. The overall converter efficiency also improves if the VIN voltage is much higher than the auxiliary voltage. Do not exceed 14 V with an externally applied VCC voltage. The VCC regulator series pass MOSFET includes a body diode (see Section 7.2) between VCC and VIN that must not be forward biased in normal operation. Therefore, the auxiliary VCC voltage must never exceed the VIN voltage.

In high voltage applications take extra care to ensure the VIN pin does not exceed the absolute maximum voltage rating of 76 V. Voltage ringing on the VIN line during line transients that exceeds the Absolute Maximum Ratings can damage the IC. Both careful PCB layout and the use of quality bypass capacitors placed close to the VIN and GND pins are essential.