FSTU32X800QSP

Overview

The FSTU32X800QSP is a 20-bit high-speed CMOS bus switch manufactured by Fairchild Semiconductor, now part of onsemi. It features precharged outputs and -2V undershoot protection via the UHC circuit. The device consists of two 10-bit switches controlled by an OE signal. When enabled, it provides a low on-resistance connection between ports A and B. In the disabled state, Port B is precharged to a selectable BiasV voltage through a 10-kΩ resistor. It operates with a supply voltage (VCC) range of 4.0V to 5.5V and supports input voltages from 0V to 5.5V.

Feature Summary

• Undershoot Hardened Circuit protects I/Os against negative voltage excursions down to -2.0V.
• Output precharge function minimizes live insertion noise by biasing Port B when the switch is open.
• Soft enable turn-on mechanism reduces bus-to-bus charge sharing during activation.
• Control inputs are TTL level compatible for flexible logic interfacing.

Applications

• High-speed data bus switching in digital systems
• Live insertion applications requiring noise reduction
• TTL-compatible interface buffering

Procurement Notes

Verify that the component corresponds to the MQA48A package variant. Confirm the manufacturer lineage from Fairchild Semiconductor to onsemi for documentation accuracy. Ensure the specific QSP suffix matches the required quarter-size very small outline package specifications for your design integration.

Selection Notes

Select this component when designing circuits requiring 20-bit parallel bus switching with integrated undershoot protection. It is suitable for applications needing precharged outputs to mitigate noise during hot-swap scenarios. Verify that the operating voltage requirements align with the 4.0V to 5.5V VCC range and that the 48-lead QVSOP package fits the board layout constraints.

Part Context

This device belongs to the Fairchild Switch family, utilizing proven CMOS technology similar to the FST3384 series. It is designed for high-speed applications where minimal propagation delay and ground bounce noise are critical. The integration of the UHC circuit distinguishes it from standard bus switches by providing robust protection against signal undershoot.

Replacement Considerations

The FSTU32X384 is a similar 20-bit low-power bus switch with undershoot protection but lacks the precharged output feature. Verify functional compatibility regarding the absence of the precharge capability if substituting.

FAQ

How does the device handle live insertion?

It precharges the B Port to a selectable BiasV voltage through a 10-kΩ resistor when the switch is open, which minimizes live insertion noise.

What is the maximum negative voltage the I/Os can withstand?

The integrated Undershoot Hardened Circuit allows the I/Os to withstand undershoot down to -2.0V without turning the switch on or causing damage.