Intel® Celeron® Processor for PGA370 up to 1.40 GHz on 0.13 µ Process
3.3.1
Overshoot/Undershoot Guidelines
Overshoot (or undershoot) is the absolute value of the maximum voltage above the nominal high
voltage or below VSS. The overshoot guideline limits transitions beyond VCC or VSS due to the fast
signal edge rates (see Figure 21 for non-AGTL signals). The processor can be damaged by repeated
overshoot events on 1.25 V or 1.8 V tolerant buffers if the charge is large enough (i.e., if the
overshoot is great enough). Permanent damage to the processor is the likely result of excessive
overshoot/undershoot. Violating the overshoot/undershoot guideline will also make satisfying the
ringback specification difficult. The overshoot/undershoot guideline is 0.3 V and assumes the
absence of diodes on the input. These guidelines should be verified in simulations without the on-
chip ESD protection diodes present because the diodes will begin clamping the 1.25 V and 2.5 V
tolerant signals beginning at approximately 0.7 V above the appropriate supply and 0.7 V below
VSS. If signals are not reaching the clamping voltage, this will not be an issue. A system should not
rely on the diodes for overshoot/undershoot protection as this will negatively affect the life of the
components and make meeting the ringback specification very difficult.
Table 28. 33 MHz CMOS Signal Group Overshoot/Undershoot Tolerance
Maximum Pulse Duration at
Tcase = 69 °C (ns)
Maximum Pulse Duration at
Tcase = 71 °C (ns)
Maximum Pulse Duration at
Tcase = 72 °C (ns)
Overshoot/
Undershoot
Magnitude
(V)
AF =
0.01
AF =
0.1
AF =
1
AF =
0.01
AF =
0.1
AF =
1
AF =
0.01
AF =
0.1
AF =
1
2.38
2.33
2.28
2.23
2.18
2.13
2.08
35
60
60
60
60
60
60
3.5
8.0
18
41
60
60
60
0.35
0.8
1.8
4.1
9.0
21
19
40
60
60
60
60
60
1.9
4.0
8.0
18
0.19
0.40
0.80
1.80
3.75
8.00
16.00
17
36
60
60
60
60
60
1.7
3.6
7.7
16
0.17
0.36
0.77
1.60
3.42
7.12
14.5
37.5
60
34
60
60
60
60
Note: The undershoot guideline limits transitions exactly as described for the ATGL signals. See
Figure 20.
3.3.2
Ringback Specification
Ringback refers to the amount of reflection seen after a signal has switched. The ringback
specification is the voltage that the signal rings back to after achieving its maximum absolute
value. See Figure 21 for an illustration of ringback. Excessive ringback can cause false signal
detection or extend the propagation delay. The ringback specification applies to the input pin of
each receiving agent. Violations of the signal ringback specification are not allowed under any
circumstances for non-AGTL signals.
Ringback can be simulated with or without the input protection diodes that can be added to the
input buffer model. However, signals that reach the clamping voltage should be evaluated further.
See Table 29 for the signal ringback specifications for non-AGTL signals for simulations at the
processor pins.
48
Datasheet
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