Mature devices - Altera Corporation

Altera Corporation 1

Using Altera Devices in

Multiple-Voltage Systems

June 1999, ver. 1.0 Application Note 107

A-AN-107-01

Introduction

Although the 5.0-V interface has been a standard for decades, the move

towards advanced process technology requires a shift to lower voltage

levels. In today’s market, printed circuit boards (PCBs) are assembled

with a mixture of 5.0-V, 3.3-V, 2.5-V, and 1.8-V devices. To accommodate

this mixture seamlessly, it is essential that these devices interface with

systems of differing supply voltages.

Altera’s MultiVolt

I/O interface meets the increasing demand for

compatibility with devices of different voltages. The MultiVolt interface

separates the power supply voltage from the output voltage, enabling

Altera

devices to interface with other devices using different voltage

levels on the same PCB. Altera has taken further steps by incorporating

support for hot-socketing, which refers to inserting or removing cards or

boards from a back plane during operation. Hot-socketing is a common

requirement for high-reliability systems. Altera offers a variety of devices

that support hot-socketing.

This application note discusses several features that allow you to

implement Altera devices in multiple voltage systems without damaging

the device or the system, including:

■

MultiVolt Interface

■

Hot-Socketing

■

Power-Up Sequence

■

Power-On Reset (POR)

MultiVolt

Interface

Advanced-process devices require 3.3-V, 2.5-V, or 1.8-V power supplies.

However, other devices on a board may still use 5.0-V or 3.3-V supplies.

A programmable logic device (PLD) must interface with these other

devices. In the future, even lower voltage levels will be required for

smaller process geometries.

To accommodate the need to interface with a variety of devices, Altera has

developed the broadest range of MultiVolt I/O interfaces. The MultiVolt

I/O interface allows devices to communicate in a mixed-voltage design

environment. The device core and I/O pins can be powered-up with

separate supply voltages. The

VCCINT

pins power the device core and the

VCCIO

pins power the I/O buffers for most devices. All device

VCCIO

pins

that have MultiVolt capability should be supplied from the same voltage

level (e.g., 5.0 V, 3.3 V, 2.5 V, or 1.8 V). See Figure 1.

2 Altera Corporation

AN 107: Using Altera Devices in Multiple-Voltage Systems

Figure 1. MultiVolt I/O Interface Feature for Altera Devices

Note (1)

Note:

(1) The Altera device can interact with each voltage one at a time, but not

simultaneously (except APEX

20KE and MAX

7000B devices, which can have

different V

CCIO

levels simultaneously).

5.0-V Device Compatibility

5.0-V devices—FLEX

10K, MAX 9000, MAX 7000S, MAX 7000,

FLEX 8000, and 5.0-V FLEX 6000 devices—support interfaces to 3.3-V and

5.0-V devices.

3.3-V Device Compatibility

When using 3.3-V devices—FLEX

10KA, 3.3-V FLEX 6000, MAX 7000A,

and MAX 3000A devices—the

VCCINT

pins must be connected to a 3.3-V

power supply. The

VCCIO

pins can be connected to either a 2.5-V or 3.3-V

power supply, depending on the output requirements. When the

VCCIO

pins are connected to a 3.3-V power supply, the output high is 3.3 V and

is therefore compatible with 3.3-V or 5.0-V systems. The device can also

drive other 3.3-V tolerant, 2.5-V devices. Inputs for the above devices can

always be driven by 2.5-V, 3.3-V, or 5.0-V systems, except for EPF10K50V

and EPF10K130V devices, which can only be driven by 3.3-V and 5.0-V

systems.

Altera

Device 3.3-V

Device

2.5-V

Device

5.0-V

Device

Altera Corporation 3

AN 107: Using Altera Devices in Multiple-Voltag e Systems

2.5-V Device Compatibility

The

VCCINT

pins on 2.5-V APEX 20K, FLEX 10KE, and MAX 7000B devices

must be connected to a 2.5-V power supply. The

VCCIO

pins can be

connected to either a 2.5-V or 3.3-V power supply, depending on the

output requirements. When the

VCCIO

pins are connected to a 2.5-V

power supply, the output levels are compatible with 2.5-V systems. When

the

VCCIO

pins are connected to a 3.3-V power supply, the output high is

3.3 V and is therefore compatible with 3.3-V or 5.0-V systems. The device

can also drive other 3.3-V tolerant, 2.5-V devices.

The APEX 20K device family incorporates a wider variety of I/O

standards. This device family is covered in

Application Note 117

(Using Selectable I/O Standards in Altera Devices)

Table 1 summarizes Altera MultiVolt I/O support.

Table 1. Altera MultiVolt I/O Support

Notes (1)

(2)

Device V

CCINT

(V)

CCIO

(V)

Input Signal (V) Output Signal (V)

1.8 2.5 3.3 5.0 1.8 2.5 3.3 5.0

FLEX 10K,

FLEX 8000,

FLEX 6000 (5.0 V),

MAX 7000S,

MAX 9000

5.0 5.0

vv v

3.3

vv vv

EPF10K50V,

EPF10K130V 3.3 3.3

vv vv

FLEX 10KA,

FLEX 6000 (3.3 V),

MAX 7000A,

MAX 3000A

3.3 3.3

vvv vv

2.5

vvv v

FLEX 10KE 2.5 3.3

vvv vv

2.5

vvv v

APEX 20K

(3)

2.5 3.3

vv v

2.5

vv v

APEX 20KE

(3)

(4)

1.8 3.3

vvv v

2.5

vvv v

1.8

vvv v

MAX 7000B 2.5 3.3

vvv v

2.5

vvv v

1.8

vvv v

4 Altera Corporation

AN 107: Using Altera Devices in Multiple-Voltage Systems

Notes:

(1) All

FLEX 10K devices support 3.3-V I/O pins with a 5.0-V core, except 84-pin plastic J-lead chip carrier (PLCC) and 240-pin

quad ﬂat pack (QFP) packages. All MAX 7000S devices—e xcept EPM7032S and EPM7064S de vices in the 44-pin PLCC and

thin quad ﬂat pack (TQFP) packages—support 3.3-V I/O pins with a 5.0-V core.

(2) The EPF8282V I/O pins are not 5.0-V tolerant. Altera does not recommend driving 5.0-V signals to these 3.3-V devices.

(3) APEX 20K and APEX 20KE I/O pins are not 5.0-V tolerant.

(4) For more information on APEX 20KE MultiVolt support, see

Application Note 117 (Using Selectable I/O Standards in Altera

Devices)

5.0-V TTL Compatibility

Altera 5.0-V tolerant devices are 5.0-V TTL compatible. For example, a

3.3-V device can drive a 5.0-V device, and in return, can be driven by a

5.0-V device. Additionally, when the

VCCIO

pins on a 5.0-V device are

connected to 3.3 V, the I/O pins can still be driven by 5.0-V signals

because the I/O buffers are still 5.0-V tolerant.

5.0-V CMOS Compatibility

Altera’s 5.0-V devices with NMOS-only output buffers meet 5.0-V TTL

levels. When the voltage at the output pin exceeds approximately

3.8 V, the NMOS pull-up transistor goes to cut-off mode. Therefore, you

can use an external pull-up resistor to pull up the signal to 5.0 V. See

Figure 2.

Figure 2. 5.0-V Altera Device Compatibility with 5.0-V CMOS Devices

Note (1)

Note:

(1) When V

OUT

≥

3.8 V, transistor M1 is cut-off. As a result, the external resistor (R

EXT

)

can pull up the output node (V

OUT

) to a full rail level of 5.0 V.

VSS

VOUT

REXT

5.0-V CMOS

Device

5.0 V

VCCIO = 5.0 V or 3.3 V

Altera Corporation 5

AN 107: Using Altera Devices in Multiple-Voltag e Systems

To make Altera low-voltage device outputs compatible with 5.0-V CMOS

devices, configure the output pins as open-drain pins and use an external

pull-up resistor. The low-voltage devices have a CMOS driver; if V

OUT

CCIO

, the PMOS pull-up transistor still conducts if the pin is driving

high, preventing an external pull-up resistor from pulling the signal to

5.0 V (see Figure 3). 5.0-V tolerant, 3.3-V and 2.5-V devices can also drive

5.0-V CMOS devices.

Figure 3. CMOS Output Buffer for Altera Low-Voltage Devices

Note (1)

Note:

(1) When V

OUT

> V

CCIO

, the current will flow as shown above. As a result, the V

OUT

node cannot be pulled to 5.0 V.

To pull the output of a low-voltage device up to the V

(input high) level

of a 5.0-V CMOS device, use an open-drain pin driving a trace that is

pulled up to 5.0 V through an external pull-up resistor (see Figure 4).

Choose a pull-up resistor that is small enough for a sufficient signal rise

time, but large enough that it does not violate the I

(output low)

specifications of devices driving that trace.

VSS

VOUT

REXT

5.0-V CMOS

Device

5.0 V

VCCIO = 3.3 V or 2.5 V

6 Altera Corporation

AN 107: Using Altera Devices in Multiple-Voltage Systems

Figure 4. Low-Voltage Altera Device Compatibility with 5.0-V CMOS

Devices

Note (1)

Note:

(1) To pull the V

OUT

to the rail of 5.0 V, ensure that the output is an open drain.

Therefore, the external pull-up resistor (R

EXT

) pulls V

OUT

to 5.0 V.

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 device operates successfully because a 5.0-V input is within

its input specification.

Hot-Socketing

Hot-socketing, hot-swap, or hot plug-in refers to inserting or removing a

board or device into or out of a system board while system power is on.

For a system to support hot-socketing, plug-in or removal of a board must

not damage the system or interrupt system operation.

Hot-Socketing in Altera Devices

The following Altera 3.3-V, 2.5-V, and 1.8-V devices are designed to

support hot-socketing without special design requirements:

■

APEX 20K

■

APEX 20KE

■

FLEX 10KA

■

FLEX 10KE (except EPF10K100B devices)

■

3.3-V FLEX 6000

■

MAX 7000AE

■

MAX 7000B

■

MAX 3000A

VCCIO

VSS

VOUT

REXT

5.0-V CMOS

Device

5.0 V

VIN

Open Drain

Altera Corporation 7

AN 107: Using Altera Devices in Multiple-Voltag e Systems

The following features have been implemented in Altera devices to ease

the hot-socketing process:

■

Devices can be driven before power-up with no damage to the device.

■

Devices do not drive out before or during power-up.

■

Signal pins do not drive the V

CCIO

or V

CCINT

power supplies.

Devices Can Be Driven before Power-Up

Devices that do not support hot-socketing may be damaged if the pins are

driven before the device is powered-up. For Altera devices that support

hot-socketing, the device I/O pins, dedicated input pins, and dedicated

clock pins can be driven before or during power-up without damaging

the device.

Devices Do Not Drive Out before or during Power-Up

Devices that do not support hot-socketing may interrupt system

operation or cause contention by driving out before or during power-up.

In Altera devices that support hot-socketing, I/O pins are tri-stated before

and during power-up and configuration, and will not drive out.

Signal Pins Cannot Drive the V

CCIO

or V

CCINT

Power Supply

Devices that do not support hot-socketing may be powered-up through

their signal pins (when plugged into a live board) causing the power

supplies to short-out. This irregular power-up can damage both the

driving and driven devices and can disrupt card power-up.

For Altera devices that support hot-socketing, there is no current path

from the I/O, dedicated input, or dedicated clock pins to the

VCCIO

VCCINT pins before and during power-up; therefore, these devices cannot

be powered-up through the I/O pins. Some Altera devices have weak

pull-up resistors; these resistors are activated as the device is powered by

the VCCIO and VCCINT pins. As a result, Altera devices that support hot-

socketing may be inserted into (or removed from) a powered-up system

board without damage or without interfering with the operation of the

system board. During hot-socketing, these devices will not affect signal

integrity of the back plane.

8 Altera Corporation
AN 107: Using Altera Devices in Multiple-Voltage Systems
The DC operating conditions in each device data sheet specify the device 
input leakage current. For most devices, this leakage current is 10 µA. 
During hot-socketing, DC leakage current into an I/O pin may be higher. 
Table 2 shows this value for Altera devices that support hot-socketing.
Notes:
(1) These devices are 5.0-V tolerant.
(2) Includes current from the weak pull-up resistors in the I/O cell.
(3) The OE1 and GCLRn pins in MAX 7000AE and MAX 3000A devices may be driven 
up to 3.6 V during hot-socketing. After VCCINT and VCCIO reach the 
recommended operating conditions, these pins are 5.0-V tolerant.
(4) All other pins in MAX 700AE and MAX 3000A devices may be driven up to 5.75 V 
during hot-socketing.
(5) These 2.5-V devices are 3.3-V tolerant.
A possible concern regarding hot-socketing is the potential for latch-up. 
Latch-up can occur when electrical subsystems are hot-socketed into an 
active system. During hot-socketing, the signal pins may be connected 
and driven by the active system before the power supply can provide 
current to the device’s VCC and ground planes. This condition can lead to 
latch-up and cause a low-impedance path from VCC to ground within the 
device. As a result, the device expends a large amount of current, possibly 
causing electrical damage. All Altera devices are immune to latch-up 
when operated within device specifications, including hot-socketing.
Power-Up 
Sequence
Altera devices are designed to operate in multiple-voltage environments 
where it may be difficult to control power sequencing. Therefore, the 
devices are designed to accommodate any possible power-up sequence. 
The following sections address the power-up sequence for different 
voltage levels.
When VCCIO and VCCINT are supplied from different power sources to an 
Altera device, a delay between VCCIO and VCCINT may occur. Normal 
operation does not occur until both power supplies are in their 
recommended operating range.
Table 2. Hot-Socket DC Leakage Current for Altera Devices
Device Condition Max Unit
FLEX 10KA,
FLEX 10KE,
FLEX 6000 (3.3 V)
VCC = 0 V
VIN ≤ 5.75 V (1)
300 (2) µA
MAX 7000AE,
MAX 3000A VCC = 0 V
VIN ≤ 3.6 V (3)
300 (2) µA
VCC = 0 V
VIN ≤ 5.75 V (1), (4)
300 (2) µA
APEX 20K
MAX 7000B VCC = 0 V
VIN ≤ 4.1 V (5)
300 (2) µA

Altera Corporation 9

AN 107: Using Altera Devices in Multiple-Voltag e Systems

When VCCINT is powered-up, the IEEE Std. 1149.1 Joint Test Action Group

(JTAG) circuitry is active. If TMS and TCK are connected to VCCIO and

VCCIO is not powered-up, the JTAG signals are left floating. Thus, any

transition on TCK can cause the state machine to transition to an unknown

JTAG state, leading to incorrect operation when VCCIO is finally powered-

up. To disable the JTAG state during the power-up sequence, TCK should

be pulled low to ensure that an inadvertent rising edge does not occur on

TCK.

fFor more information, refer to Application Note 100 (In-System

Programmability Guidelines).

3.3-V, 2.5-V, or 1.8-V APEX, FLEX & MAX Devices

Because APEX 20K, APEX 20KE, FLEX 10KA, FLEX 10KE,

MAX 7000B, 3.3-V FLEX 6000, MAX 7000AE, and MAX 3000A devices can

be used in a multi-voltage environment, they are designed specifically to

tolerate any possible power-up sequence (where appropriate). VCCINT

and VCCIO can supply power in either sequence. 5.0-V, 3.3-V, 2.5-V, or

1.8-V input signals can drive these devices before VCCINT or VCCIO is

applied without special precautions; the only exception is that the OE1 and

nGCLR pins on MAX 7000AE and MAX 3000A devices must not exceed

3.6 V until VCCIO and VCCINT reach the recommended operating level.

You can change the VCCIO supply voltage from 3.3 V to 2.5 V or vice-versa

while the board is powered-up. However, you must ensure that the

VCCINT and VCCIO power supplies stay within the correct device

operating conditions.

FLEX and configuration devices can power-up in either order, but you

must ensure that the nSTATUS and CONF_DONE pull-up resistors are

connected to the same voltage as the configuration device. This

connection avoids driving signals into a configuration device that is not

powered.

2.5-V and 1.8-V devices are the only Altera devices that can have a VCCIO

voltage level higher than the VCCINT level.

5.0-V FLEX & MAX Devices

When VCCIO powers-up, MAX devices can drive out without the core

being powered-up. This power-up sequence does not damage MAX

devices and their functionality is not affected, but it may interfere with the

function of the system that contains MAX devices.

10 Altera Corporation

AN 107: Using Altera Devices in Multiple-Voltage Systems

Because of possible interference with system functionality, Altera does

not recommend driving 5.0-V MAX device input signals or relying on the

output of the device before VCCINT is powered-up.

FLEX and configuration devices can power-up in either order, but you

must ensure that the nSTATUS and CONF_DONE pull-up resistors are

connected to the same voltage as the configuration device. This

connection avoids driving signals into a configuration device that is not

powered.

Power-On

Reset

The state of a system at power-up is an important consideration in

designing a circuit. When power is applied to an Altera device, the POR

event occurs only if VCC reaches the recommended operating range

within a certain period of time (specified as a maximum VCC rise time). A

POR event does not occur if these conditions are not met because slower

rise times can cause incorrect device initialization and functional failure.

The maximum VCC rise time for FLEX 10K, FLEX 8000, and

FLEX 6000 devices is 100 ms and should be monotonic (during VCC rise

time, the slope is zero or positive). For MAX devices, the maximum VCC

rise time is infinite as long as it is monotonic.

Altera’s device registers are cleared or set (MAX 7000AE, MAX 7000B, and

MAX 3000A devices) during power-on reset. If you are using the

NOT-Gate Push-Back option in the QuartusTM and MAX+PLUS® II

software, the registers power-up active-high. The NOT-Gate Push-Back

option is an advanced logic synthesis option, which allows the compiler’s

logic synthesizer module to push an inversion (i.e., a NOT gate) back

through a register and implement it on that register’s D input.

Once the VCCINT power supply reaches the specified operating range, it

must remain at that range. If VCCINT does not remain in the range, the

operation is not guaranteed until VCCINT re-enters the specified operating

range.

APEX & FLEX Devices

Before the VCC supply reaches the recommended operating range, the

I/O pins are tri-stated, with the exception of APEX 20K and FLEX 10KE

devices that have pull-up resistors at the I/O pins. During POR, the

registers are cleared and the tri-state is released. Once the VCC power

supply reaches a stable and reliable operating voltage and after nCONFIG

has gone high, the actual device configuration begins. During

configuration, the I/O pins are tri-stated.

Altera Corporation 11

AN 107: Using Altera Devices in Multiple-Voltag e Systems

MAX Devices

Before the VCC supply reaches the recommended operating range for

MAX 7000AE, MAX 7000B, and MAX 3000A devices, the I/O pins are tri-

stated. During POR, the registers are cleared or set. After POR, the tri-state

is released and the I/O pins are in user mode and function as

programmed (if the device has been previously programmed

successfully).

For other MAX 7000—including MAX 7000E, MAX 7000S, and

MAX 7000A—and MAX 9000 devices, the I/O pins are undefined until

VCC reaches the recommended operating range. During POR, the

registers are cleared and the tri-state is released. After POR, the I/O pins

are in user mode and function as programmed.

1The power-up state of latches is undefined in all Altera devices

except MAX 5000 devices. In MAX 5000 devices, latches

power-up low.

During POR, the device configures I/O pins, clears device registers, and

releases tri-states.

Conclusion PCBs often contain a mix of 5.0-V, 3.3-V, 2.5-V, and 1.8-V devices. The

MultiVolt interface enables the device core to run at a specific voltage

(5.0 V, 3.3 V, 2.5 V, or 1.8 V), while keeping the I/O pins compatible with

5.0-V, 3.3-V, 2.5-V, or 1.8-V logic levels. Altera’s MultiVolt interface allows

you to incorporate newer generation devices with devices of varying

voltage levels seamlessly. Altera has taken further steps by designing

devices which allow VCCINT and VCCIO to power-up in either sequence

and by incorporating support for hot-socketing.

Altera, APEX, APEX 20K, APEX 20KE, EPF10K50V, EPF10K130V, EPF8282V, EPM7032S, EPM7064S, FLEX,

FLEX 10K, FLEX 10KA, FLEX 10KE, FLEX 8000, FLEX 6000, MAX, MAX 9000, MAX 7000, MAX 7000A,

MAX 7000AE, MAX 7000B, MAX 7000S, MAX 3000A, MAX 5000, MAX+PLUS, MAX+PLUS II, MultiVolt, and

Quartus are trademarks and/or service marks of Altera Corporation in the United States and other countries.

Altera acknowledges the trademarks of other organizations for their respective products or services

mentioned in this document, specifically: Synplify is a registered trademark of Synplicity. Altera products are

protected under numerous U.S. and foreign patents and pending applications, maskwork rights, and

copyrights. Altera warrants performance of its semiconductor products to current specifications in accordance

with Altera’s standard warranty, but reserves the right to make changes to any products and services at any

time without notice. Altera assumes no responsibility or liability arising out of the application

or use of any information, product, or service described herein except as expressly agreed to

in writing by Altera Corporation. Altera customers are advised to obtain the latest version of

device specifications before relying on any published information and before placing orders

for products or services.

101 Innovation Drive

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(408) 544-7000

http://www.altera.com

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AN 107: Using Altera Devices in Multiple-Voltage Systems

12 Altera Corporation

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