S1L60000 Datasheet, PDF (144/230 Pages) Epson Company – GATE ARRAY

Chapter 10: Pin Layout Considerations
b) Overshoot, undershoot and ringing
The equivalent inductance in the output pins causes noises known as “overshoot,”
“undershoot” and “ringing.” This equivalent inductance is marked by L₃ in Figure
10-1. Because inductance has the property of storing energy, this overshoot,
undershoot or ringing is the result of the output becoming either low or high. When
there is a transition, the overshoot and undershoot is proportional to the size of the
current to the rate of change of the current.
The most effective way to reduce overshoot and undershoot is to use output cells with
relatively small drive current, and there is a tendency for the overshoot and undershoot
to be reduced when there is a relatively large load capacitance. Because of this, there
is a need for caution when using cells with especially large current driving capabilities.
(3) Isolating Input Pins and Output Pins
Separating the input pin group from the output pin group in the pin layout is an important
technique for reducing the impact of noise.
Because input pins and bi-directional pins in the input state are especially susceptible to
noise, one should avoid mixing these pins with output pins whenever possible, and the
input pin group, the output pin group, and the bi-directional pin group should be separated
from each other by the power supply pins (V_DD, V_SS).
Output pins
V_DD
V_SS
V_SS
V_DD
V_SS
V_DD
Bid pins
Figure 10-2 Example of Separating Input Pins and Output Pins
GATE ARRAY S1L60000 SERIES
DESIGN GUIDE
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