BQ3285LDSSTRG4

Overview

The Texas Instruments BQ3285LDSSTRG4 is a low-power CMOS real-time clock (RTC) and calendar designed for battery-backed operation in 3V systems. It provides time-of-day counting, a 100-year calendar with automatic leap-year adjustment, and programmable alarm features. The device includes 242 bytes of general nonvolatile storage accessible via a multiplexed address/data bus. Key electrical parameters include a supply voltage range of 2.7V to 3.6V, a typical standby current of 100µA, and a battery backup current of less than 0.5µA. It supports selectable Intel or Motorola bus timing and offers three maskable interrupt sources: periodic, alarm, and update-ended.

Feature Summary

• Functionally compatible with DS1285 and closely matches MC146818A pin configuration for direct replacement in IBM AT-compatible computers.
• Provides 242 bytes of general nonvolatile SRAM and 14 bytes of clock/calendar registers with BCD or binary format options.
• Features a 32.768kHz output for power management and system wake-up capability via alarm interrupt active in battery-backup mode.
• Supports selectable Intel or Motorola bus timing with multiplexed AD0–AD7 address/data lines.

Applications

• IBM AT-compatible computers requiring direct RTC replacement.
• Battery-powered embedded systems needing low-power timekeeping.
• Industrial controllers utilizing alarm interrupts for system wake-up.
• Data logging devices requiring nonvolatile storage for timestamps.

Procurement Notes

Verify the specific suffix 'DG4' indicates lead-free status and RoHS compliance as per Texas Instruments documentation. Confirm the package type corresponds to the SSOP variant associated with this part number. Ensure the application circuit includes a 32.768kHz crystal with 6pF load capacitance and a dedicated 3V backup cell on the BC pin for proper operation during power failures.

Selection Notes

Select the bq3285L variant for systems operating between 2.7V and 3.6V; use the bq3285E for 4.5V to 5.5V systems. Ensure the host processor supports the required multiplexed bus interface or can emulate the necessary AS, DS, and R/W signals. Verify that the external crystal meets the specified load capacitance and aging requirements to maintain accuracy within the commercial temperature range of 0°C to +70°C.

Part Context

The bq3285E/L series serves as a legacy real-time clock solution for microprocessor-based systems. The bq3285L specifically targets lower voltage applications compared to the bq3285E. This component bridges the gap between standard RTC functions and nonvolatile memory needs, eliminating the need for separate battery-backed RAM chips in many PC-compatible designs.

Replacement Considerations

The datasheet states functional compatibility with the DS1285 and close matching of the MC146818A pin configuration. Direct pin-for-pin replacement should be verified against the specific system's bus timing requirements (Intel vs. Motorola). Ensure the replacement part supports the same voltage range (2.7V–3.6V for L variant) and package footprint.