During operation, it is possible for V_EXT to deviate from the nominal DC value due to external factors such as line transients, load transients (if V_EXT is loaded), and single-event transients caused by radiation. The SEE report for the TPS7H4104-SEP, Single-Event Effects (SEE) Radiation Report of the TPS7H4104-SEP shows and discusses the results of testing the TPS7H4104-SEP under a heavy-ion beam. While no SET events 3% or greater in magnitude were observed, a theoretical 3% transient can be induced on V_EXT in simulation to observe the effects on V_OUT with different nominal levels of V_EXT.

In the simulation, a -3% transient was injected directly onto the V_EXT rail with rise and fall times of 10µs. Three different nominal V_EXT levels were tested, and transient magnitude was adjusted for each V_EXT condition to -3% of nominal. Figure 4-3 shows the results for all three V_EXT levels displayed on a single plot.

The plot above shows that for larger values of V_EXT, the same percentage deviation from the nominal voltage will produce a smaller disturbance on V_OUT. The cause of this unintuitive relationship is the voltage drop across R_B1, and the V_REF voltage. The current flowing through R_B1 is not determined by the total potential between GND and V_EXT, but rather between V_EXT and V_REF. Since the magnitude of the upset on V_EXT was determined by the V_EXT to GND voltage, after V_REF is subtracted from V_EXT, smaller values of V_EXT will end up with larger percentage upsets because V_REF is a larger portion of the value.

In addition, a modified TPS7H4104EVM with V_EXT and a low-voltage output channel in a similar configuration as described in section 3 and simulated in section 4 was exposed to a heavy ion beam with an LET of 75MeV. No SET events with a magnitude greater than 2.5% were observed on V_OUT.