In most applications, the body diode of the external low-side power MOSFET clamps the HS node to ground. In some situations, board capacitances and inductances can cause the HS node to transiently swing several volts below ground, before the body diode of the external low-side MOSFET clamps this swing. When used in conjunction with the UCC27288, the HS node can swing below ground as long as specifications are not violated and conditions mentioned in this section are followed.

HS must always be at a lower potential than HO. Pulling HO more negative than specified conditions can activate parasitic transistors which may result in excessive current flow from the HB supply. This may result in damage to the device. The same relationship is true with LO and VSS. If necessary, a Schottky diode can be placed externally between HO and HS or LO and VSS to protect the device from this type of transient. The diode must be placed as close to the device pins as possible in order to be effective.

Ensure that the HB to HS operating voltage is 16 V or less. Hence, if the HS pin transient voltage is –5 V, then VDD (and thus HB) is ideally limited to 11 V to keep the HB to HS voltage below 16 V. Generally when HS swings negative, HB follows HS instantaneously and therefore the HB to HS voltage may not significantly overshoot.

Low ESR bypass capacitors from HB to HS and from VDD to VSS are essential for proper operation of the gate driver device. The capacitor should be located at the leads of the device to minimize series inductance. The peak currents from LO and HO can be quite large. Any series inductances with the bypass capacitor causes voltage ringing at the leads of the device which must be avoided for reliable operation.

Based on application board design and other operating parameters, along with HS pin, other pins such as inputs, HI and LI, might also transiently swing below ground. To accommodate such operating conditions UCC27288 input pins are capable of handling absolute maximum of -5V. As explained earlier, based on the layout and other design constraints, some times the outputs, HO and LO, might also see transient voltages for short durations. Therefore, UCC27288 gate drivers can also handle -2 V 100 ns transients on output pins, HO and LO.