SNVS953G December 2012 – May 2021 LM25018
The LM25018 device contains an internal high voltage linear regulator with a nominal output of 7.6 V. The input pin (VIN) can be connected directly to the line voltages up to 48 V. The VCC regulator is internally current limited to 30 mA. The regulator sources current into the external capacitor at VCC. This regulator supplies current to internal circuit blocks including the synchronous MOSFET driver and the logic circuits. When the voltage on the VCC pin reaches the undervoltage lockout threshold of 4.5 V, the IC is enabled.
The VCC regulator contains an internal diode connection to the BST pin to replenish the charge in the gate drive boot capacitor when SW pin is low.
At high input voltages, the power dissipated in the high voltage regulator is significant and can limit the overall achievable output power. As an example, with the input at 48 V and switching at high frequency, the VCC regulator can supply up to 7 mA of current, resulting in 48 V × 7 mA = 336 mW of power dissipation. If the VCC voltage is driven externally by an alternate voltage source, between 8.55 V and 13 V, the internal regulator is disabled. This reduces the power dissipation in the IC.