Hot-Socketing Feature Implementation in Cyclone II Devices
Figure 4–1. Hot-Socketing Circuit Block Diagram for Cyclone II Devices
Power-On
Reset
Monitor
Output
Weak
Pull-Up
R
Output Enable
Resistor
Voltage
Tolerance
Control
Hot Socket
PAD
Output
Pre-Driver
Input Buffer
to Logic Array
The POR circuit monitors VCCINT voltage level and keeps I/O pins
tri-stated until the device is in user mode. The weak pull-up resistor (R)
from the I/O pin to VCCIO keeps the I/O pins from floating. The voltage
tolerance control circuit permits the I/O pins to be driven by 3.3 V before
VCCIO and/or VCCINT are powered, and it prevents the I/O pins from
driving out when the device is not in user mode.
f
For more information, see the DC Characteristics & Timing Specifications
chapter in Volume 1 of the Cyclone II Device Handbook for the value of the
internal weak pull-up resistors.
Figure 4–2 shows a transistor level cross section of the Cyclone II device
I/O buffers. This design ensures that the output buffers do not drive
when VCCIO is powered before VCCINT or if the I/O pad voltage is higher
than VCCIO. This also applies for sudden voltage spikes during hot
socketing. The VPAD leakage current charges the voltage tolerance control
circuit capacitance.
4–4
Cyclone II Device Handbook, Volume 1
Altera Corporation
February 2007
ALTERA [ ALTERA CORPORATION ]
