BQ4850YMA-85

Overview

The bq4850Y is a non-volatile SRAM module integrating 524,288 words by 8 bits of static RAM with an accessible real-time clock (RTC). It features an internal lithium battery and quartz crystal. The device operates at +5V with a typical standby current of 3 mA. Data retention is guaranteed for a minimum of 10 years without power. It includes automatic power-fail deselection and write protection when VCC falls below the power-fail detect voltage of 4.37V typical. The RTC counts seconds through years in BCD format using dual-port registers updated once per second.

Feature Summary

• Integrated 512K x 8 SRAM with non-volatile data retention via internal battery
• Real-time clock with calendar functionality (seconds to year) in BCD format
• Automatic power-fail detection and write-protection circuitry
• Software clock calibration capability for improved accuracy

Applications

• Industrial control systems requiring persistent timekeeping
• Data logging applications needing non-volatile storage
• Embedded systems replacing standard SRAMs with added clock functions

Procurement Notes

Verify that the internal battery remains disconnected until the first application of VCC to ensure maximum capacity. Confirm that the system design accommodates the 32-pin DIP module dimensions and pinout compatibility with industry-standard 512K x 8 SRAM sockets.

Selection Notes

Select this component when a combined non-volatile memory and real-time clock solution is required in a single package. Ensure the operating environment stays within the 0°C to +70°C temperature range. Verify that the 5V supply voltage meets the recommended operating conditions of 4.5V to 5.5V.

Part Context

The bq4850Y is part of Texas Instruments' RTC Module family designed to directly replace industry-standard SRAMs. It fits into many EPROM and EEPROM sockets without special write timing requirements. The device eliminates limitations on the number of write cycles associated with traditional non-volatile memories.

Replacement Considerations

The datasheet notes pin-compatibility with industry-standard 512K x 8 SRAMs. No specific substitute part numbers are listed in the provided documentation.

FAQ

How is clock accuracy maintained over time?

The bq4850Y offers onboard software clock calibration. Users can adjust calibration bits in the control register to compensate for frequency shifts due to temperature, achieving greater than ±1 minute per month accuracy.

What happens during a power failure?

When VCC falls below the power-fail detect voltage (VPFD), the device automatically deselects and write-protects itself. The internal battery switches on to preserve data, and outputs go high impedance.

How does the device handle clock updates during read operations?

The clock registers are dual-port. To prevent reading data in transition, users can set the read bit (D6) in the control register to 1 to halt updates. Once the frozen time is retrieved, the bit should be reset to 0 to resume updates.