5–4
Chapter 5: Using MAX V Devices in Multi-Voltage Systems
5.0-V Device Compatibility
Figure 5–3 shows MAX V device compatibility with 5.0-V CMOS devices.
Figure 5–3. MAX V Device Compatibility with 5.0-V CMOS Devices
5.0 V 0.5 V
3.3 V
V
V
CCIO
CCIO
V
CCIO
(1)
REXT
Open Drain
VOUT
Model as RINT
5.0-V CMOS
Device
A
VIN
VSS
Note to Figure 5–3:
(1) This diode is only active after power-up. MAX V devices require an external diode if driven by 5.0 V before
power-up.
The open-drain pin never drives high, only low or tri-state. When the open-drain pin
is active, it drives low. When the open-drain pin is inactive, the pin is tri-stated and
the trace pulls up to 5.0 V by the external resistor. The purpose of enabling the I/O
clamp diode is to protect the MAX V device’s I/O pins. The 3.3-V VCCIO supplied to
the I/O clamp diodes causes the voltage at point A to clamp at 4.0 V, which meets the
MAX V device’s reliability limits when the trace voltage exceeds 4.0 V. The device
operates successfully because a 5.0-V input is within its input specification.
1
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 in the
5M1270Z and 5M2210Z devices and all the I/O pins in the 5M40Z, 5M80Z, 5M160Z,
5M240Z, and 5M570Z devices.
The pull-up resistor value must be small enough for a sufficient signal rise time, but
large enough so that it does not violate the IOL (output low) specification of the
MAX V devices.
The maximum MAX V device IOL depends on the programmable drive strength of the
I/O output. Table 5–1 lists the programmable drive strength settings that are available
for the 3.3-V LVTTL/LVCMOS I/O standard for MAX V devices. The Quartus II
software uses the maximum current strength as the default setting. The PCI I/O
standard is always set to 20 mA with no alternate setting.
Table 5–1. 3.3-V LVTTL/LVCMOS Programmable Drive Strength (Part 1 of 2)
I/O Standard
IOH/IOL Current Strength Setting (mA)
16
8
3.3-V LVTTL
MAX V Device Handbook
December 2010 Altera Corporation
INTEL [ INTEL ]
