Hot Socketing & Power-On Reset
IIOPIN is the current at any user I/O pin on the device. This specification
takes into account the pin capacitance, but not board trace and external
loading capacitance. Additional capacitance for trace, connector, and
loading needs must be considered separately. For the AC specification,
the peak current duration is 10 ns or less because of power-up transients.
For more information, refer to the Hot-Socketing & Power-Sequencing
Feature & Testing for Altera Devices white paper.
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 extends a large amount of current, possibly
causing electrical damage. Nevertheless, Stratix II devices are immune to
latch-up when hot-socketing.
The hot socketing feature turns off the output buffer during the power-up
event (either VCCINT, VCCIO, or VCCPD supplies) or power down. The hot-
socket circuit will generate an internal HOTSCKTsignal when either
VCCINT, VCCIO, or VCCPD is below threshold voltage. The HOTSCKTsignal
will cut off the output buffer to make sure that no DC current (except for
weak pull up leaking) leaks through the pin. When VCC ramps up very
slowly, VCC is still relatively low even after the POR signal is released and
the configuration is finished. The CONF_DONE, nCEO, and nSTATUSpins
fail to respond, as the output buffer can not flip from the state set by the
hot socketing circuit at this low VCC voltage. Therefore, the hot socketing
circuit has been removed on these configuration pins to make sure that
they are able to operate during configuration. It is expected behavior for
these pins to drive out during power-up and power-down sequences.
Hot Socketing
Feature
Implementation
in Stratix II
Devices
Each I/O pin has the following circuitry shown in Figure 4–1.
Altera Corporation
May 2007
4–3
Stratix II Device Handbook, Volume 1
ALTERA [ ALTERA CORPORATION ]
