When the external MOSFETs turn OFF during the conditions, such as overvoltage cut-off, reverse current blocking, EN causing an interruption of the current flow, the input line inductance generates a positive voltage spike on the input and output inductance generates a negative voltage spike on the output. The peak amplitude of voltage spikes (transients) depends on the value of inductance in series to the input or output of the device. These transients can exceed the Absolute Maximum Ratings of the device if steps are not taken to address the issue.

Typical methods for addressing transients include:

• Minimizing lead length and inductance into and out of the device
• Using large PCB GND plane
• Using a Schottky diode across the output and GND to absorb negative spikes
• Using a low value ceramic capacitor (C_(IN) to approximately 0.1 μF) to absorb the energy and dampen the transients.

The approximate value of input capacitance can be estimated with Equation 7.

Equation 7.

where

• V_(IN) is the nominal supply voltage
• I_(LOAD) is the load current
• L_(IN) equals the effective inductance seen looking into the source
• C_(IN) is the capacitance present at the input

Some applications can require additional Transient Voltage Suppressor (TVS) to prevent transients from exceeding the Absolute Maximum Ratings of the device. These transients can occur during EMC testing such as automotive ISO7637 pulses.

The circuit implementation with optional protection components (a ceramic capacitor, TVS, and Schottky diode) is shown in Figure 10-1.

^* Optional components needed for suppression of transients

Figure 10-1 Circuit Implementation With Optional Protection Components for LM74720-Q1