PROASIC3E datasheet(23/37 Pages) ACTEL

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I/O Structures in IGLOOe and Pro ASIC3E Devices

v1.4

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.

Figure 13 • Solution 4

Solution 4

2.5 V

5.5 V

2.5 V

Requires one board resistor.

Available for LVCMOS 2.5 V / 5.0 V.

I/O Input

Rext

On-Chip

Clamp

Diode

Table 14 • Comparison Table for 5 V–Compliant Receiver Solutions

Solution

Board Components

Speed

Current Limitations

Two resistors

Low to High1 Limited by transmitter's drive strength

Resistor and Zener 3.3 V

Medium

Limited by transmitter's drive strength

Bus switch

High

N/A

Minimum resistor value2,3,4,5

R = 47

Ω at TJ = 70°C

R = 150

Ω at TJ = 85°C

R = 420

Ω at TJ = 100°C

Medium

Maximum diode current at 100% duty cycle, signal

constantly at 1

52.7 mA at TJ = 70°C / 10-year lifetime

16.5 mA at TJ = 85°C / 10-year lifetime

5.9 mA at TJ = 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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