AN1009

Anatomy of a parasitic bipolar transistor

Figure 2: "Substrate VCC versus negative undershoots" superimposes three pairs of curves:

three negative undershoot pulses of 100, 500 and 1000 ns duration; and the corresponding

Thus, we see that the effect on the substrate voltage is proportional to the duration of the

negative undershoot pulse. It is also proportional to its magnitude (its amplitude). It is also

proportional to the number of pins that receive the negative undershoot pulse (the example,

above, is the effect of just one pin on the chip going negative).

DocID006391 Rev 2

3/7

Negative Undershoot

-1V

5

8

.

3

s

n

0

2

4

-

µs

-1.2 volts for 1

-1.2 volts for 500ns

-1.2 volts for 100ns

Substrate VCC

4V

not

trig'd

M

C1

500mV

400ns

µs