7.3.3 GATE

Provides the high side (above VCC) gate drive for Q1. It is controlled by the internal gate drive amplifier, which provides a pull-up of 22 µA from an internal charge pump and a strong pulldown to ground of 75 mA (minimum). The pulldown current is a nonlinear function of the amplifier overdrive; it provides small drive for small overloads, but large overdrive for fast reaction to an output short. There is a separate pull-down of 2 mA to shut Q1 off when EN or UVLO cause this to happen. An internal clamp protects the gate of Q1 (to OUT) and generally eliminates the need for an external clamp in almost all cases for devices with 20-V V_GS(MAX) ratings; an external Zener may be required to protect the gate of devices with V_GS(MAX) < 16 V. A small series resistance (R5) of 10 Ω must be inserted in the gate lead if the C_ISS of Q1 > 200 pF, otherwise use 33 Ω for small MOSFETs.

A capacitor can be connected from GATE to ground to create a slower inrush with a constant current profile without affecting the amplifier stability. Add a series resistor of about 1 kΩ to the gate capacitor to maintain the gate clamping and current limit response time. Adding capacitance across Q1 gate to source requires some series damping resistance to avoid high-frequency oscillations.