BQ4842YMA-85

Overview

The BQ4842YMA-85 is a non-volatile 1,048,576-bit SRAM organized as 131,072 words by 8 bits, featuring an integrated real-time clock and CPU supervisor. It combines static storage RAM with an internal lithium battery, quartz crystal, clock circuitry, and power-fail detection in a 32-pin DIP module. The device provides automatic write protection during power failures and ensures data retention for at least 10 years without external power. It supports software calibration to maintain accuracy within ±1 minute per month.

Feature Summary

• Integrated 128K x 8 NVSRAM with accessible real-time clock and control registers
• Internal lithium battery providing minimum 10-year data retention
• Automatic power-fail deselection and write-protection circuit
• Programmable watchdog timer and microprocessor reset generator
• Software-adjustable clock calibration for temperature compensation

Applications

• Systems requiring non-volatile memory with persistent timekeeping
• Industrial controllers needing watchdog timer functionality
• Embedded systems replacing standard SRAMs with RTC capabilities
• Equipment requiring alarm and periodic interrupt features

Procurement Notes

Verify the specific speed grade suffix (-85) corresponds to the required access times of 85 ns maximum. Confirm that the 32-pin MA package matches the target socket or PCB footprint. Ensure the application design accounts for the initial battery disconnection state until VCC is first applied.

Selection Notes

Select this component when a combined SRAM and RTC solution is preferred over discrete components. The -85 speed option is suitable for systems with cycle times up to 85 ns. Consider the 0°C to +70°C operating temperature range for environmental compatibility. Verify that the system can accommodate the open-drain INT and RST outputs requiring pull-up resistors.

Part Context

This part belongs to the bq4842Y series of RTC modules from Texas Instruments. It is designed to directly replace industry-standard 128K x 8 SRAMs while adding real-time clock and supervisor functions. The module integrates all necessary components for timekeeping and memory preservation into a single plastic DIP package.

Replacement Considerations

Publicly confirmed substitute part numbers are not available in the provided documentation. When replacing standard SRAMs, ensure the host system supports the dual-port register access for clock updates without interrupting normal memory operations.