
Lattice Semiconductor FPGA
Lattice Semiconductor
Successful Place and Route
16-5
Board trace AC loading (Cbac): 60 pf.
Board trace parasitic capacitance (Cb): 5 pf.
Port controller input capacitance (Cp) :9 pf.
FPGA device input capacitance (Co): 9 pf.
The above information was specified under the following environmental conditions:
Maximum ambient temperature (Ta): 70 (C.
Estimated Power Consumption (Q): 2 W.
680 PBGAM Package Thermal resistance (
j) at 0 feet per minute (fpm) airflow: 13.4 °C/W.
The goal of this exercise is to compute the following device I/O constraints:
1. Input setup specification.
2. Input hold specification.
3. Maximum output propagation delay.
4. Minimum output propagation delay.
5. Output loading.
6. Temperature.
The only parameter which can be obtained from the above is the device junction temperature:
Tj =
j * Q - Ta
= 13.4 * 2 + 70
= 96.8 °C
The required constraints can be computed as follows:
1. Input setup specification
= P - PDMAXp - PDMAXb - Tskew
= 30 - 18 - 2 - 1
= 9 ns
2. Input hold specification
= PDMINp + PDMINb - Tskew
= 3 + 1 - 1
= 3 ns
3. Output maximum propagation delay requirement
= P - TSp - PDMAXb - Tskew
= 30 - 5 - 6 - 1
= 18 ns
4. Output minimum propagation delay requirement
= Thp - PDMINb + Tskew
= 3 - 1 + 1
= 3 ns
5. Output loading
= Cbac + Cb + Cp
= 60 + 5 + 9
= 74 pf
The preference file to use for this example is shown in
Figure 16-3. For more preference language syntax and
examples, refer to the Constraints & Preferences section of the ispLEVER on-line help system.