7.3.2 V_CC Regulator

The LM34925 device contains an internal high voltage linear regulator with a nominal output of 7.6 V. The input pin (V_IN) can be connected directly to the line voltages up to 100 V. The V_CC regulator is internally current limited to 30 mA. The regulator sources current into the external capacitor at V_CC. This regulator supplies current to internal circuit blocks including the synchronous MOSFET driver and the logic circuits. When the voltage on the V_CC pin reaches the Undervoltage Lockout threshold of 4.5 V, the IC is enabled.

The V_CC 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 V_CC regulator may supply up to 7 mA of current resulting in 48 V × 7 mA = 336 mW of power dissipation. If the V_CC 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.