Chapter 5: Using MAX V Devices in Multi-Voltage Systems
5–7
Recommended Operating Conditions for 5.0-V Compatibility
As shown in Figure 5–5, R1 = 5.0 V/135 mA.
The values usually shown in the data sheets reflect typical operating conditions.
Subtract 20% from the data sheet value for guard band. When you subtract the 20%
from the previous example, the R1 value is 30.
Select R2 so that the MAX V device’s IOH specification is not violated. For example, if
the above device has a maximum IOH of 8 mA, given the I/O clamp diode,
VIN = VCCIO + 0.7 V = 3.7 V. Given that the maximum supply load of a 5.0-V device
(VCC) is 5.5 V, calculate value of R2 as follows:
Equation 5–2.
5.5 V – 3.7 V – 8 mA 30
R2 = ----------------------------------------------------------------------------------- = 194
8 mA
This analysis assumes worst-case conditions. If your system does not see a wide
variation in voltage-supply levels, you can adjust these calculations accordingly.
Because 5.0-V device tolerance in MAX V devices requires the use of the I/O clamp,
and this clamp is activated only after power-up, 5.0-V signals may not be driven into
the device until it is configured. The I/O clamp diode is only supported in the
5M1270Z and 5M2210Z devices’ I/O Bank 3. You must have an external protection
diode for the other I/O banks for the 5M1270Z and 5M2210Z devices and all the I/O
pins in the 5M40Z, 5M80Z, 5M160Z, 5M240Z, and 5M570Z devices.
Recommended Operating Conditions for 5.0-V Compatibility
As mentioned earlier, a 5.0-V tolerance can be supported with the I/O clamp diode
enabled with external series/pull-up resistance. To guarantee long term reliability of
the device’s I/O buffer, there are restrictions on the signal duty cycle that drive the
MAX V I/O, which is based on the maximum clamp current. Table 5–3 lists the
maximum signal duty cycle for the 3.3-V VCCIO given a PCI clamp current-handling
capability.
Table 5–3. Maximum Signal Duty Cycle
VIN (V) (1)
4.0
ICH (mA) (2)
5.00
Max Duty Cycle (%)
100
90
50
30
17
10
5
4.1
11.67
4.2
18.33
4.3
25.00
4.4
31.67
4.5
38.33
4.6
45.00
Notes to Table 5–3:
(1) VIN is the voltage at the package pin.
(2) The ICH is calculated with a 3.3-V VCCIO. A higher VCCIO value will have a lower ICH value with the same VIN.
December 2010 Altera Corporation
MAX V Device Handbook
ALTERA [ ALTERA CORPORATION ]
