8.1.1 HS Transient Voltages Below Ground
The HS node will always be clamped by the body diode of the lower external FET. In some situations, board resistances and inductances can cause the HS node to transiently swing several volts below ground. The HS node can swing below ground provided:
- HS must always be at a lower potential than HO. Pulling HO more than -0.3V below HS can activate parasitic transistors resulting in excessive current to flow from the HB supply possibly resulting in damage to the IC. 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 GND to protect the IC from this type of transient. The diode must be placed as close to the IC pins as possible in order to be effective.
- HB to HS operating voltage should be 15V or less . Hence, if the HS pin transient voltage is -5V, VDD should be ideally limited to 10V to keep HB to HS below 15V.
- A low ESR bypass capacitor between HB to HS as well as VDD to VSS is essential for proper operation. The capacitor should be located at the leads of the IC to minimize series inductance. The peak currents from LO and HO can be quite large. Any series inductances with the bypass capacitor will cause voltage ringing at the leads of the IC which must be avoided for reliable operation.