TIBPAL20L8-5C Datasheet, PDF (24/35 Pages) Texas Instruments – HIGH-PERFORMANCE IMPACT-X PAL CIRCUITS

TIBPAL20R4-5C, TIBPAL20R6-5C, TIBPAL20R8-5C
HIGH-PERFORMANCE IMPACT-X ™ PAL^® CIRCUITS
SRPS010F – D3353, OCTOBER 1989 – REVISED SEPTEMBER 1992
By using the described test circuit, MTBF can be determined for several different values of ∆t (see Figure 9).
Plotting this information on semilog scale demonstrates the metastable characteristics of the selected flip-flop.
Figure 11 shows the results for the TIBPAL20’-5C operating at 1 MHz.
10 ⁹
10 yr
10 ⁸
1 yr
10 ⁷
1 mo
10 ⁶
1 wk
10 ⁵
1 day
10 ⁴
1 hr
10 ³
10 ²
1 min
10 ¹
10 s
fclk = 1 MHz
fdata = 500 kHz
0 10 20 30 40 50 60 70
∆ t (ns)
Figure 11. Metastable Characteristics
From the data taken in the above experiment, an equation can be derived for the metastable characteristics at
+ ^{* other clock frequencies.}
The metastable equation: ¹
MTBF
fSCLK x fdata x C1 e ^{( C2 x Dt)}
The constants C1 and C2 describe the metastable characteristics of the device. From the experimental data,
these constants can be solved for: C1 = 4.37 X 10^–3 and C2 = 2.01
+ ^{* * Therefore}
1
MTBF
fSCLK x fdata x 4.37 x 10 ³ e ^{( 2.01 x Dt)}
definition of variables
DUT (Device Under Test): The DUT is a 5-ns registered PLD programmed with the equation Q : = D.
MTBF (Mean Time Between Failures): The average time (s) between metastable occurrences that cause a
violation of the device specifications.
f_SCLK (system clock frequency): Actual clock frequency for the DUT.
f_data (data frequency): Actual data frequency for a specified input to the DUT.
C1: Calculated constant that defines the magnitude of the curve.
C2: Calculated constant that defines the slope of the curve.
t_rec (metastability recovery time): Minimum time required to guarantee recovery from metastability, at a given
MTBF failure rate. t_rec = ∆t – t_pd (CLK to Q, max)
∆t: The time difference (ns) from when the synchronizing flip-flop is clocked to when its output is sampled.
The test described above has shown the metastable characteristics of the TIBPAL20R4/R6/R8-5C series. For
additional information on metastable characteristics of Texas Instruments logic circuits, please refer to TI
Applications publication SDAA004, ”Metastable Characteristics, Design Considerations for ALS, AS, and LS
Circuits.’’
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