TIBPAL16R4-5C, TIBPAL16R6-5C, TIBPAL16R8-5C

HIGH-PERFORMANCE IMPACT-X

™ PAL® CIRCUITS

SRPS011D – D3359, OCTOBER 1989 – REVISED SEPTEMBER 1992

POST OFFICE BOX 655303

• DALLAS, TEXAS 75265

24

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 TIBPAL16’-5C operating at 1 MHz.

0

1020

3040

506070

10 1

10 2

10 3

10 4

10 5

10 6

10 7

10 8

10 9

∆t – Time Difference – ns

fclk = 1 MHz

fdata = 500 kHz

10 yr

1 yr

1 mo

1 day

1 wk

1 hr

1 min

10 s

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

+ f

SCLK

xf

data

xC1e (*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

+ f

SCLK

xf

data

x4.37x 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.

fSCLK (system clock frequency): Actual clock frequency for the DUT.

fdata (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.

trec (metastability recovery time): Minimum time required to guarantee recovery from metastability, at a given

MTBF failure rate. trec = ∆t – tpd (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 TIBPAL16R4/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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