7.3.2 VCC Regulator

The LM5161 contains an internal high voltage linear regulator with a nominal output voltage of 7.3 V (typical). The VCC regulator is internally current limited to 30 mA (minimum). This regulator supplies power to internal circuit blocks including the synchronous FET gate driver and the logic circuits. When the voltage on the VCC pin reaches the undervoltage lockout (V_CC(UV)) threshold of 3.98 V (typical), the IC is enabled. An external capacitor at the VCC pin stabilizes the regulator and supplies transient VCC current to the gate drivers. An internal diode connected from VCC to the BST pin replenishes the charge in the high-side gate drive bootstrap capacitor when the SW pin is low.

In high input voltage applications, the power dissipated in the regulator is significant and can limit the efficiency and maximum achievable output power. The LM5161 allows the internal VCC regulator power loss to be reduced by supplying the VCC voltage via a diode from an external voltage source regulated between 9 V and 13 V. The external VCC bias can be supplied from the LM5161 converter output rail if the regulation voltage is within this range. When the VCC pin of the LM5161 is raised above the regulation voltage (7.3 V typical), the internal regulator is disabled and the power dissipation in the IC is reduced.