The A54SX-A and RTSX-SU series devices are quite similar in many ways. However, there are significant differences in a number of aspects. Those differences will be the subject of this application note. This application note applies to UMC produced devices only.
The A54SX-A series of devices are used for commercial, industrial and automotive, and military high-reliability applications, as well as for usage in spaceflight prototypes. The RTSX-SU series of devices is designed specifically for spaceflight usage or in other radiation environments.
Architecture and Performance
Architecturally, the A54SX-A and the RTSX-SU devices are very similar. One significant difference is that the RTSX-SU supports a 5V CMOS input standard, raising the input threshold, and giving the designer improved noise immunity for a logic '0' on the input pin. A second difference is in implementation of the IEEE 1149.1 JTAG TRST* pin. For the space grade RTSX-SU device, the TRST* pin is both a dedicated pin and hardwired directly to the TAP controller. For the A54SX-A series of devices the TRST* pin is programmable via an antifuse as either the TRST* or a user I/O function.
From a performance perspective, each model of device must be analyzed separately, as there are both circuit differences as well as process differences. In general, the A54SX-A devices have higher performance and tighter control of delays for parameters such as clock skew. For the power on transient, there is an additional delay in the space grade RTSX-SU device which delays the output buffers coming out of tri-state by approximately 50 ns that is not present in the A54SX-A series devices.
Total Dose: The RTSX-SU devices have modifications that support increased total ionizing dose capability. Without these modifications, it was found in the RTSX-SU/MEC devices that propagation delay was very sensitive to total ionizing dose and limited the performance rating.
Single Event Upset and Transient: The R-Cell in the space grade RTSX-SU devices are implemented with the K-Latch that provides redundancy and an asynchronous feedback network such that the flip-flops are effectively made single event upset (SEU) hard without the need for any clock to scrub the triplet. The clock distribution circuits in the RTSX-SU devices incorporate design features to harden them against single event transients (SETs).
Single Event Latchup: Some models of the A54SX-A series devices are very sensitive to single event latchup (SEL). This sensitivity is on a lot-specific basis.
One measure of antifuse stress, for this class of device, is the ratio of the peak operating current through the antifuse to the programming current through the antifuse.
The RTSX-SU series devices have lower stress levels for the programmed antifuse than their commercial/industrial/military A54SX-A counterparts. Specifically:
- One factor which reduces the stress levels is that the RTSX-SU series devices incorporate series resistors at the output of each R-Cell, C-Cell, and I/O Cell which are not present in the A54SX-A series devices. This reduces the peak usage current through the programmed antifuse in the space grade devices. The peak usage current in the A54SX-A is 24% to 55% higher in the A54SX-A series FPGAs when compared to the RTSX-SU devices.
- Note that the RTSX-SU devices are built using the 0.25 Ám design rules while the A54SX-A devices were scaled down to 0.22 Ám. As a result, the RTSX-SU antifuses' programming current is 14% higher then the A54SX-A devices. Additional current during programming will develop a stronger and more robust programmed antifuse for the "low current antifuses."
The above two factors contribute to a lower stress level (ratio of peak operating current to programming current) for the RTSX-SU programmed antifuse when compared with its A54SX-A counterpart, providing additional reliability margin for the space grade device.
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Last Revised: February 03, 2010
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