PROASIC3E Datasheet, PDF (23/37 Pages) Actel Corporation – I/O Structures in IGLOOe and ProASIC3E Devices

I/O Structures in IGLOOe and Pro ASIC3E Devices
Solution 4
The board-level design must ensure that the reflected waveform at the pad does not exceed the
voltage overshoot/undershoot limits provided in the datasheet. This is a requirement to ensure
long-term reliability.
Solution 4
I/O Input
5.5 V
Rext
2.5 V _On-Chip
Clamp
Diode
2.5 V
Requires one board resistor.
Available for LVCMOS 2.5 V / 5.0 V.
Figure 13 • Solution 4
Table 14 • Comparison Table for 5 V–Compliant Receiver Solutions
Solution
Board Components
1
Two resistors
Speed
Current Limitations
Low to High¹ Limited by transmitter's drive strength
2
Resistor and Zener 3.3 V
Medium Limited by transmitter's drive strength
3
Bus switch
High
N/A
4
Minimum resistor value^2,3,4,5 Medium Maximum diode current at 100% duty cycle, signal
constantly at 1
R = 47 Ω at T_J = 70°C
R = 150 Ω at T_J = 85°C
R = 420 Ω at T_J = 100°C
52.7 mA at T_J = 70°C / 10-year lifetime
16.5 mA at T_J = 85°C / 10-year lifetime
5.9 mA at T_J = 100°C / 10-year lifetime
For duty cycles other than 100%, the currents can be
increased by a factor of 1 / (duty cycle).
Example: 20% duty cycle at 70°C
Maximum current = (1 / 0.2) × 52.7 mA = 5 × 52.7 mA =
263.5 mA
Notes:
1. Speed and current consumption increase as the board resistance values decrease.
2. Resistor values ensure I/O diode long-term reliability.
3. At 70°C, customers could still use 420 Ω on every I/O.
4. At 85°C, a 5 V solution on every other I/O is permitted, since the resistance is lower (150 Ω ) and the current
is higher. Also, the designer can still use 420 Ω and use the solution on every I/O.
5. At 100°C, the 5 V solution on every I/O is permitted, since 420 Ω are used to limit the current to 5.9 mA.
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