This design example shows how to use Altera® MAX® II, MAX V, and MAX 10 to implement voltage level shifters between different devices in a mixed-voltage design environment.

The supported Altera devices are an excellent choice to implement voltage level shifters. Their low power make them ideal for voltage level translator applications. Specifically, this applies to multi-level voltage systems where it can be critical to maintain a specific power-on sequence of the multiple voltages involved.

Devices on one circuit board can potentially use many different supply voltages, such as 5V, 3.3V, 2.5V, 1.8V, 1.5V, and 1.2V. Therefore, the buses connected to a system can have different voltage standards that can lead to voltage-level conflicts. MAX II devices are designed to interface directly with 1.5-V, 1.8-V, 2.5-V, and 3.3-V signals and can be used to eliminate these conflicts. MAX V and MAX 10 supports direct interface with 1.2-V, 1.5-V, 1.8-V, 2.5-V, and 3.3-V signals.

The supported devices can interface with other devices using different voltage levels because the core power supply voltage (V_CCINT or V_{CC_ONE} for MAX 10) is separate from the device output voltage (VCCIO). A few applications for voltage level shifting are:

• Interfacing microprocessors with peripheral devices, timers, and transceivers that are operating at different I/O standards and levels
• Driving more than one set of GPIO pins having different I/O standards

The detailed description of the implementation is based on the MAX II devices. This application can also be implemented in MAX V and MAX 10 devices.

MAX II devices are designed to tolerate all types of power-on sequences making them ideal for multiple voltage systems where it is critical to maintain a particular power-on sequence.

You can configure each I/O bank to operate at a particular voltage using its V_CCIO pin. A single device can support 1.2-V, 1.5-V, 1.8-V, 2.5-V, and 3.3-V interfaces and each individual bank can support a different standard. In addition, each I/O bank can support multiple standards with the same VCCIO for input and output pins. The number of I/O banks for a particular device depends on its part number.

The I/O buffer of the MAX II devices is programmable and supports a wide range of I/O voltage standards. Each I/O bank can be programmed to comply with a different I/O standard, such as the following:

• 3.3-V LVTTL/LVCMOS
• 2.5-V LVTTL/LVCMOS
• 1.8-V LVTTL/LVCMOS
• 1.5-V LVCMOS

In addition to these standards that are supported by all MAX II devices (on the EPM1270 and EPM2210 devices) I/O Bank 3 also includes a 3.3-V PCI I/O standard interface capability. MAX II devices with MultiVolt core I/O operation capability allow the core and I/O blocks of the device to be powered up with separate supply voltages. The VCCINT pins supply power to the device core and the VCCIO pins supply power to the device I/O buffers. Therefore, the MAX II devices can receive inputs from, or drive outputs to devices with different voltage levels by shifting from one value on one I/O bank to a different value on another I/O bank.

You can implement this design with an EPM240 device or any other MAX II devices, all of which have more than one I/O bank. Eight inputs are powered at 2.5V and eight outputs are powered at 1.8V to achieve 2.8V to 1.8V level translation. This design example is implemented in three basic steps that involve determining the physical pins (pin assignments), setting pin attributes in the Quartus® II software and relevant buffers assignment, and signal paths between input pins and output pins (this is accomplished by the source code).

Design example adapted for Altera MAX 10 FPGAs by:

Orchid Technologies Engineering and Consulting, Inc.

Maynard, Massachusetts 01754

TEL: 978-461-2000

WEB: www.orchid-tech.com

EMAIL: info@orchid-tech.com