I/O Structures in IGLOO and ProASIC3 Devices
7- 18
v1.1
be avoided by driving the input LOW when a weak pull-down resistor is used and driving it HIGH
when a weak pull-up resistor is used.
This current draw can occur in the following cases:
In Active and Static modes:
–
Input buffers with pull-up, driven LOW
–
Input buffers with pull-down, driven HIGH
–
Bidirectional buffers with pull-up, driven LOW
–
Bidirectional buffers with pull-down, driven HIGH
–
Output buffers with pull-up, driven LOW
–
Output buffers with pull-down, driven HIGH
–
Tristate buffers with pull-up, driven LOW
–
Tristate buffers with pull-down, driven HIGH
In Flash*Freeze mode:
–
Input buffers with pull-up, driven LOW
–
Input buffers with pull-down, driven HIGH
–
Bidirectional buffers with pull-up, driven LOW
–
Bidirectional buffers with pull-down, driven HIGH
Electrostatic Discharge Protection
Low-power flash devices are tested per JEDEC Standard JESD22-A114-B.
These devices contain clamp diodes at every I/O, global, and power pad. Clamp diodes protect all
device pads against damage from ESD as well as from excessive voltage transients.
All IGLOO and ProASIC3 devices are tested to the following models: the Human Body Model (HBM)
with a tolerance of 2,000 V, the Machine Model (MM) with a tolerance of 250 V, and the Charged
Device Model (CDM) with a tolerance of 200 V.
Each I/O has two clamp diodes. One diode has its positive (P) side connected to the pad and its
negative (N) side connected to VCCI. The second diode has its P side connected to GND and its N side
connected to the pad. During operation, these diodes are normally biased in the off state, except
when transient voltage is significantly above VCCI or below GND levels.
In 30 k gate devices, the first diode is always off. In other devices, the clamp diode is always on and
cannot be switched off.
By selecting the appropriate I/O configuration, the diode is turned on or off. Refer to
on page 7-19 for more information about the I/O standards and the clamp diode.
The second diode is always connected to the pad, regardless of the I/O configuration selected.