Cyclone® V Device Handbook: Volume 1: Device Interfaces and Integration

ID 683375
Date 10/18/2023
Document Table of Contents

10.3. Hot-Socketing Implementation

The hot-socketing feature tri-state the output buffer during power up and power down of the power supplies. When these power supplies are below the threshold voltage, the hot-socketing circuitry generates an internal HOTSCKT signal.

Hot-socketing circuitry prevents excess I/O leakage during power up. When the voltage ramps up very slowly, I/O leakage is still relatively low, even after the release of the POR signal and configuration is complete.

Note: The output buffer cannot flip from the state set by the hot-socketing circuitry at very low voltage. To allow the CONF_DONE and nSTATUS pins to operate during configuration, the hot-socketing feature is not applied to these configuration pins. Therefore, these pins will drive out during power up and power down.
Figure 181. Hot-Socketing Circuitry for Cyclone® V Devices

The POR circuitry monitors the voltage level of the power supplies and keeps the I/O pins tri-stated until the device is in user mode. The weak pull-up resistor (R) in the Cyclone® V input/output element (IOE) is enabled during configuration download to keep the I/O pins from floating.

The 3.3-V tolerance control circuit allows the I/O pins to be driven by 3.3 V before the power supplies are powered and prevents the I/O pins from driving out before the device enters user mode.