DS1221S

The DS1221S from Analog Devices is a CMOS nonvolatile controller chip that addresses the challenge of making CMOS RAM nonvolatile. It continuously monitors incoming power and automatically protects data during power loss by inhibiting chip enable outputs and switching to battery power. This controller integrates a 2-to-4 decoder, enabling the management of up to four CMOS RAM chips.

The device operates over a voltage range of 4.5V to 5.5V and is specified for an operating temperature range of 0°C to 70°C. It is available in a 16-pin SOIC surface mount package, saving valuable PC board space. An optional security feature can prevent unauthorized access to the memory space. The low-leakage CMOS process ensures precise voltage detection with minimal battery consumption, making it suitable for applications requiring reliable data retention.

This nonvolatile controller is designed to work in conjunction with standard CMOS RAMs and a lithium battery to achieve nonvolatile operation. Its features include automatic power-fail detection, write protection during power loss, and the ability to test battery condition on power-up. The DS1221S is a solution for applications needing to preserve critical data even when primary power is interrupted.