Digital isolators with overvoltage tolerant inputs improve robustness against signal overshoot caused by parasitic elements in the system. PCB trace inductance, package parasitics, connector capacitance, and other related effects can produce transient voltage spikes that exceed the supply voltage.

On a digital isolator without overvoltage-tolerant inputs, the input structure operates within a specified input-voltage range relative to its supply (Figure 1-1). During fast signal transitions, parasitic inductance and capacitance can cause the input voltage to temporarily exceed the supply rail. These transient overvoltage conditions can stress the input circuitry, particularly when the overshoot occurs repeatedly at high switching frequencies.

On a digital isolator with overvoltage-tolerant inputs, the input voltage is completely independent from the supply voltage (Figure 2-1) and allows the isolator to tolerate input voltages above their supply voltage within a specified range. This provides additional design margin against PCB and system-level parasitics and can improve robustness in applications with fast switching signals, long traces, connectors, etc. that may generate signal overshoots.

Figure 3-4 illustrates this behavior for an ISO6441 digital isolator. The waveforms show three simultaneous signals (Table 3-5):