FG256 datasheet(37/108 Pages) ACTEL

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SX-A Family FPGAs

v5.3

2-17

Timing Characteristics

Timing characteristics for SX-A devices fall into three

categories: family-dependent, device-dependent, and

design-dependent.

The

input

and

output

buffer

characteristics are common to all SX-A family members.

Internal routing delays are device-dependent. Design

dependency means actual delays are not determined

until after placement and routing of the user’s design are

complete. The timing characteristics listed in this

datasheet represent sample timing numbers of the SX-A

devices. Design-specific delay values may be determined

by using Timer or performing simulation after successful

place-and-route with the Designer software.

Critical Nets and Typical Nets

Propagation delays are expressed only for typical nets,

which are used for initial design performance evaluation.

Critical net delays can then be applied to the most

timing-critical paths. Critical nets are determined by net

property assignment prior to placement and routing. Up

to 6 percent of the nets in a design may be designated as

critical, while 90 percent of the nets in a design are

typical.

Long Tracks

Some nets in the design use long tracks. Long tracks are

special routing resources that span multiple rows,

columns, or modules.

Long tracks employ three to five

antifuse connections. This increases capacitance and

resistance, resulting in longer net delays for macros

connected to long tracks. Typically, up to 6 percent of

nets in a fully utilized device require long tracks. Long

tracks contribute approximately 4 ns to 8.4 ns delay. This

additional delay is represented statistically in higher

fanout routing delays.

Timing Derating

SX-A devices are manufactured with a CMOS process.

Therefore, device performance varies according to

temperature, voltage, and process changes. Minimum

timing parameters reflect maximum operating voltage,

minimum

operating

temperature,

and

best-case

processing.

Maximum

timing

parameters

reflect

minimum

operating

voltage,

maximum

operating

temperature, and worst-case processing.

Temperature and Voltage Derating Factors

Table 2-13 • Temperature and Voltage Derating Factors

(Normalized to Worst-Case Commercial, TJ = 70°C, VCCA = 2.25 V)

VCCA

Junction Temperature (TJ)

–55°C

–40°C

0°C

25°C

70°C

85°C

125°C

2.250 V

0.790.800.870.89

1.001.04

1.14

2.500 V

0.740.750.820.83

0.940.97

1.07

2.750 V

0.680.690.750.77

0.870.90

0.99

FG256 Datasheet(PDF) 37 Page - Actel Corporation

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