On-Chip Hot-Socketing and Power-Sequencing Support

Hot socketing refers to the capability to insert a board into, or remove a board from, a system during operation without causing negative effects to the system or the board. It is also referred to as “hot swapping” or “hot plug-in.”

Devices in the Stratix® series and Cyclone® series FPGAs, and the MAX® series CPLDs, are designed and tested to offer robust support for on-chip hot-socketing and power-sequence protection without needing additional external devices or board manipulation.

A device must meet three criteria to be considered hot-socketable:

  • It can be driven before power up without any damage.
  • It does not drive out before power up.
  • It does not drive out during power up.

To find out more about the advantages of the on-chip hot-socketing support in Intel® FPGA devices, refer to the Intel FPGA Hot-Socketing & Power-Sequencing advantages white paper that details Intel FPGA’s hot-socketing advantages. For detailed characterization data, refer to the Hot-Socketing & Power-Sequencing Feature & Testing for Intel FPGA devices white paper.

For detailed characterization data, refer to the white paper detailing hot-socketing features and testing for Stratix, Stratix® GX, Stratix® II, Stratix® II GX, Stratix® III, Cyclone® and Cyclone® II FPGA families, and MAX® V, MAX® II, MAX® 7000AE and MAX® 3000A CPLD families.

Protection in PLDs for High-Availability Systems

Hot socketing is a critical requirement for systems that require high availability (constant system uptime), such as network storage servers or carrier-class telecommunication infrastructures, where each second of system downtime translates directly into revenue losses.

Protection in PLDs for Multi-Voltage Systems

In multi-voltage systems for which hot socketing is not required, hot-socketing and power-sequence protection capability for the PLD is still critical. In these systems, regulators are used to provide different voltage levels and can cause the power-up sequence to become unpredictable; devices that require a predetermined power-up sequence may no longer function properly.

The hot-socketing support in PLDs can alleviate problems in multi-voltage system designs because normal PLD functionality will not be influenced by the system power-up sequence. This can be vital for the common application where CPLDs are used to control the power up of other devices in very complex systems.

Table 1 outlines some example systems in different market segments that benefit from hot socketing in Intel FPGA devices.

Table 1. Examples of Systems Requiring Hot Socketing

Market Segment

Application Examples


  • Hubs
  • Routers
  • Switches

Computing Services

  • Workstations
  • Computer servers

Data Storage

  • Data switches
  • Tape automation system
  • Storage system data centers

Wireless Communications

  • Cellular basestation infrastructure

Wireline Communications

  • PBX and central office infrastructure

On-Chip Hot-Socketing and Power-Sequencing Support Advantages

There are several techniques used to ensure that PLDs function properly during hot socketing, including sequence connectors and discrete hot-swap controllers. Table 2 compares hot socketing in Intel FPGA PLDs versus using other techniques.

Table 2. Intel FPGA PLDs Vs. Alternatives

  Intel FPGA Hot-Socketable PLD1 Sequenced Connectors Hot-Swap Controller
  • Includes no-hassle, drop-in implementation
  • Normal PLD functionality not influenced by power-up sequence2
  • Includes on-chip support (no external devices or board manipulation required)3
  • Guarantees that ground and power pins mate with the backplane before signal pins
  • Includes in-rush current protection
  • Includes power-up sequence control
  • May not work for multi-voltage systems
  • Requires careful on-board power distribution
  • Requires additional external device
  • Uses more board space
  • Contradicts with the pin-mating sequence requirements
  • Requires additional investments
  • May not guarantee hot-socketing capability of the PLD I/O buffers


  1. For the actual hot-socketing specification for each PLD family, refer to the handbook or data sheet of each respective family.
  2. The hot-socketing support in the Stratix, Stratix GX, and Cyclone FPGA families and the MAX 7000AE and MAX 3000A CPLD families is verified against different power-up sequences. Detailed test set up and procedures can be found in the characterization report in the Hot-Socketing & Power-Sequencing Feature & Testing for Intel FPGA devices white paper. The Stratix II, Stratix II GX, Stratix III, Stratix® IV, Stratix® V, Cyclone II, Cyclone® III, Cyclone® IV, MAX V and MAX II device families will also support the hot-socketing feature.
  3. The APEX™ II, APEX 20K, ACEX™ 1K, Mercury™, FLEX® 10KA, FLEX 10KE, and 3.3-V FLEX® 6000 FPGA families, and the MAX 7000B CPLD family also support hot socketing. For more information, refer to AN 107: Using Intel FPGA devices in multiple-voltage systems.