In process computer design, the availability of IO lines is often insufficient for the task at hand. While GPIO extenders can be helpful, they have limitations in terms of space usage and output current capacity. However, the MIC5821YN from MICREL offers an effective solution to these challenges.

Functionality and Cascading Capability

The MIC5821YN operates similarly to other shift registers, as depicted in the figure. Notably, it features a serial data out pin, allowing multiple chips to be cascaded together. This enables the expansion of the GPIO bank to virtually unlimited sizes. For instance, linking four of these chips can provide 32 output pins. Actual data is then clocked in through the CLP and Serial Data in pins.

Functionality and Cascading Capability

High-Current Output Drivers

What sets the MIC5821YN apart is its high-current output drivers. The MICREL datasheet guarantees an output capability of up to 500mA per pin, making it suitable for powering small incandescent bulbs. However, thermal considerations necessitate output derating. The table in the datasheet specifies the maximum allowed duty cycle based on current, the number of active outputs, and ambient temperature.

High-Current Output Drivers

Performance and Housing

The shift registers demonstrate excellent performance. When supplied with a 5V TTL level, they can achieve speeds of over 5MHz. If a higher voltage is available, the datasheet claims significantly faster operation. Unfortunately, detailed information on this aspect is not provided. The MIC5821YN is available in experimenter-friendly dual inline packages, allowing easy integration into breadboarded circuits. This facilitates the prototyping process for circuits utilizing this component.

Availability and Pricing

While the MIC5821YN is not out of stock with most distributors, it is relatively expensive. OEMSecrets prices range from 1.9 to 2.5 EUR per part for quantities of 100. In comparison, normal CMOS CD4xxx shift registers are more affordable and widely available in surface mount packages (Price correct as of the date of publication).

Conclusion

When high-performance shift registers are required, the MIC5821YN offers superior capabilities compared to traditional CD4000 parts. With faster speeds and the ability to provide significant current to connected loads, it is a highly recommended choice. By opting for the MIC5821YN, users can benefit from its exceptional performance and enhanced current-handling capacity, making it an ideal solution for demanding applications.