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Texas Instruments BQ3285LSS
- Part No.:
- BQ3285LSS
- Manufacturer:
- Texas Instruments
- Category:
- Real Time Clocks
- Package:
- 24-SSOP (0.154", 3.90mm Width)
- Datasheet:
-
BQ3285LSS.pdf
- Description:
- IC REAL TIME CLOCK 24-QSOP
- Quantity:
- Payment:
- Shipping:
Inventory:148
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Product details
Overview
BQ3285LSS from Texas Instruments is a low-power, 24-pin real-time clock (RTC) IC providing time-of-day and 100-year calendar functions with alarm, battery-backup operation, and 242 bytes of nonvolatile SRAM. It operates from 2.7–3.6 V, supports Intel/Motorola bus timing via MOT pin, delivers 32.768 kHz output for power management, and draws less than 0.5 µA in battery mode - used in legacy PC motherboards, industrial controllers, and embedded systems requiring persistent timekeeping during main power loss.
For engineers reviewing the BQ3285LSS datasheet, BQ3285LSS pinout, BQ3285LSS application, or BQ3285LSS equivalent, key selection considerations include its 3V supply compatibility, wake-up alarm interrupt in backup mode, BCD/binary data format flexibility, selectable square-wave frequencies (122 µs to 500 ms), and direct functional replacement capability for DS1285 and MC146818A in AT-compatible systems.
Technical Context
The BQ3285LSS integrates a precision 32.768 kHz oscillator, frequency divider, and update cycle logic synchronized to a 1-second interval. Its register-mapped interface uses multiplexed AD0–AD7 pins with AS/DS/R/W control signals, supporting both Intel-style (ALE/RD/WR) and Motorola-style (E/Φ2/R/W) timing via the MOT pin.
Three maskable interrupt sources - periodic (122 µs–500 ms), alarm (second-to-day granularity with "don't care" byte support), and update-ended - are managed through registers A, B, and C. The SQW pin outputs programmable square waves including 32.768 kHz when OSC2–OSC0 = 011 and 32KE = 1, while INT remains active in battery-backup mode as an open-drain wake-up signal.
Key Specifications
| Parameter | Value and Actual Design Meaning |
|---|---|
| Supply Voltage | 2.7–3.6 V - enables direct integration into 3V system rails without level-shifting. |
| Battery Current | <0.5 µA at VBC = 3 V - ensures multi-year RTC operation on coin-cell backup. |
| Backup Switch-Over | VPFD = 2.53 V typical - triggers seamless transition to BC pin when main VCC drops below threshold. |
| Interrupt Sources | 3 individually maskable: periodic, alarm, update-ended - allows selective event-driven system wake-up or polling. |
| Square-Wave Output | 13 selectable frequencies (122 µs–500 ms period) + 32.768 kHz option - supports clock distribution, timer reference, or power-management signaling. |
| Data Format | BCD or binary selectable via DF bit - simplifies firmware parsing and avoids manual decimal conversion. |
| Nonvolatile Storage | 242 bytes of general-purpose SRAM - retains configuration, calibration, or logging data across power cycles. |
Pinout & Package
Package: 24-pin SSOP (Small Outline Integrated Circuit), body width 0.154 inch (3.90 mm), lead pitch 0.025 inch (0.635 mm).
| Pin/Terminal | Circuit Role | Design Meaning |
|---|---|---|
| VCC | Primary power supply input | Accepts 2.7–3.6 V; powers RTC core, registers, and I/O during normal operation. |
| VSS | Ground reference | Common return path for all internal circuits and I/O signals. |
| AD0–AD7 | Multiplexed address/data bus | Carries address during AS strobe phase, then bidirectional data during transfer phase - reduces pin count vs. dedicated lines. |
| MOT | Bus architecture select | High = Motorola timing (DS/E); low = Intel timing (RD/WR/ALE) - sets compatible control signal interpretation. |
| CS | Chip select enable | Active-low signal enabling register access only when asserted during data-transfer phase. |
| AS | Address strobe | Falling edge latches address from AD0–AD7 and EXTRAM - decouples address capture from CS timing. |
| DS | Data strobe / RD/WR proxy | In Motorola mode: controls data transfer timing; in Intel mode: substitutes for RD or WR depending on R/W state. |
| R/W | Read/write direction control | High = read cycle (outputs enabled); low = write cycle (inputs sampled) - defines data flow direction on AD0–AD7. |
| INT | Open-drain interrupt output | Asserts low on enabled events (alarm, periodic, update); remains active in battery mode - enables wake-up without VCC. |
| SQW | Programmable square-wave output | Outputs selected frequency (e.g., 32.768 kHz, 1 Hz) when SQWE = 1 - serves as system clock source or timing reference. |
| EXTRAM | Extended RAM enable | Low = access RTC registers; high = access additional 128-byte SRAM block - toggles between function and storage space. |
| RCL | RAM clear input | Pull low ≥125 ms to set all 242 storage bytes to 0xFF - provides user-initiated nonvolatile memory reset. |
| BC | 3V backup cell input | Connects to coin-cell; powers RTC and preserves registers when VCC falls below VPFD. |
| RST | Reset input | Pull low to reset control bits and place INT in high-impedance state - optional for controlled initialization. |
| X1/X2 | Crystal oscillator inputs | Accepts 32.768 kHz crystal (e.g., Daiwa DT-26, 6 pF load) - establishes precise timebase independent of system clock. |
Key Features
| Feature | Design Value |
|---|---|
| Direct IBM AT-compatible replacement | Pin- and function-compatible with DS1285 and closely matches MC146818A layout - enables drop-in upgrade in legacy PC designs. |
| Wake-up alarm in battery mode | INT remains active and functional when VCC = 0 and BC supplies power - allows low-power systems to resume operation on scheduled events. |
| Selectable data format | BCD or binary mode for time/alarm/calendar bytes via DF bit - eliminates firmware conversion overhead and reduces CPU load. |
| Automatic leap-year correction | Hardware-calculated calendar updates February length based on year modulo 4 and century rules - ensures long-term date accuracy without software intervention. |
| Daylight saving toggle | DSE bit enables automatic spring-forward/fall-back on first Sunday in April/last Sunday in October - maintains local time compliance without host processor scheduling. |
| Write protection during power fail | Auto-locks clock, calendar, and SRAM registers when VCC drops below VPFD - prevents corruption during brown-out or shutdown sequences. |
Applications
| Industrial PLC Time Stamping | Legacy PC Motherboard RTC |
|---|---|
Use Scenario: Recording sensor event timestamps in programmable logic controllers operating in unattended environments with intermittent power. IC Role / Device Role / Timing Role: Primary real-time clock and calendar with battery-backed SRAM storing last-event time and operational logs. Use Value: Maintains accurate wall-clock time and preserves timestamp history across extended outages using <1 µA battery current. |
Use Scenario: Providing BIOS-managed timekeeping and wake-on-alarm functionality in IBM AT-compatible desktop motherboards. IC Role / Device Role / Timing Role: System-level RTC replacing MC146818A with enhanced alarm and low-power features. Use Value: Enables scheduled boot, hardware-based alarm interrupts, and seamless transition to 3V operation without board redesign. |
| Medical Device Power Management | Smart Meter Calendar Scheduling |
Use Scenario: Controlling sleep/wake cycles in portable diagnostic equipment to extend battery life between charges. IC Role / Device Role / Timing Role: Low-power wake-up timer generating periodic interrupts and alarm-triggered resumption from deep sleep. Use Value: Draws <0.5 µA during backup operation and delivers precise 32.768 kHz reference for system clock recovery. |
Use Scenario: Managing tariff-based billing intervals and seasonal rate changes in electricity meters with decade-long deployment. IC Role / Device Role / Timing Role: Calendar engine with automatic leap-year and daylight saving adjustment for accurate time-of-use accounting. Use Value: Hardware-accelerated date math eliminates firmware bugs and ensures regulatory-compliant timekeeping over 10+ years. |
Equivalent & Alternatives
The following parts are listed as comparable options for similar real-time clock applications.
| Alternative Part | Technical Difference | Application Difference | Selection Advice |
|---|---|---|---|
| DS1285 | 5V-only operation (4.5–5.5 V); no 3V variant; identical pinout and register map to BQ3285LSS. | Requires level-shifting or separate 5V rail in 3V systems; lacks BQ3285LSS's ultra-low battery current. | Select DS1285 only for existing 5V designs where voltage compatibility is guaranteed and backup current is secondary. |
| M41T85 | 3.3V operation; I²C interface (vs. parallel); 56 bytes NV SRAM (vs. 242 bytes); integrated trickle-charge controller. | Requires I²C host interface and external charging circuitry; smaller memory limits logging depth. | Choose M41T85 for space-constrained, I²C-based designs prioritizing integration over memory size and parallel bus compatibility. |
Compared with DS1285 and M41T85, the BQ3285LSS uniquely combines 3V parallel-bus RTC functionality, 242-byte nonvolatile storage, sub-0.5 µA battery draw, and direct AT-compatible replacement capability - making it optimal for legacy 3V embedded systems needing maximal register compatibility and long-term data retention.
Availability
BQ3285LSS is available at Aetrix Electronics and suitable for industrial PLC time stamping, legacy PC motherboard RTC upgrades, medical device power management, smart meter calendar scheduling, and embedded system wake-up timer applications requiring stable component supply and long-lifecycle support.
Supply support for BQ3285LSS includes scheduled delivery planning, volume procurement assistance, BOM continuity management, traceable sourcing, and lifecycle availability coordination for OEM customers, industrial embedded developers, connected-device designers, and electronics production programs.
Manufacturer
Texas Instruments is a global semiconductor leader specializing in analog, embedded processing, and real-time control technologies, with decades of expertise in precision timing solutions.
The BQ3285LSS belongs to TI's real-time clock product line, designed specifically for reliable, low-power timekeeping in industrial, computing, and medical applications where battery-backed accuracy and legacy system compatibility are critical.
FAQ
What is the primary function of the BQ3285LSS?
The BQ3285LSS is a real-time clock IC that provides accurate time-of-day and 100-year calendar functions with alarm, battery-backup operation, and 242 bytes of nonvolatile SRAM. It maintains precise timing during main power loss using a 3V backup cell and supports both Intel and Motorola bus protocols via the MOT pin. Its design targets legacy PC and industrial systems requiring drop-in compatibility with DS1285 and MC146818A.
How does the BQ3285LSS handle power failure and battery switchover?
The BQ3285LSS monitors VCC and triggers automatic switchover to the BC pin when voltage drops below VPFD = 2.53 V (typical). During this transition, it write-protects clock, calendar, and SRAM registers to prevent corruption. With VBC = 3 V, the device draws less than 0.5 µA, sustaining RTC operation and data integrity for years. The BQ3285LSS also asserts the INT pin in battery mode to enable system wake-up.
Can the BQ3285LSS generate a 32.768 kHz output signal?
Yes, the BQ3285LSS can output a 32.768 kHz square wave on the SQW pin. This requires setting OSC2–OSC0 = 011 in register A, enabling SQWE = 1 in register B, and setting 32KE = 1 in register C. Unlike standard square-wave frequencies derived from the divider chain, this 32.768 kHz output is sourced directly from the oscillator - making it suitable as a stable reference for power management or external clock synchronization.
What are the interrupt capabilities of the BQ3285LSS?
The BQ3285LSS supports three individually maskable interrupt sources: periodic (122 µs to 500 ms), alarm (second-to-day granularity with "don't care" byte support), and update-ended (once per second). Each has dedicated enable and flag bits in registers B and C. The open-drain INT pin remains active in battery-backup mode, allowing wake-up from deep sleep without main power - a key feature for energy-sensitive applications using the BQ3285LSS.
Is the BQ3285LSS pin-compatible with the DS1285?
Yes, the BQ3285LSS is functionally compatible with the DS1285 and shares the same 24-pin DIP/SOIC/SSOP footprint and register-level interface. However, the BQ3285LSS operates at 2.7–3.6 V (vs. DS1285's 4.5–5.5 V), includes enhanced low-power features like <0.5 µA battery current, and adds selectable BCD/binary data format and daylight saving adjustment - making it a direct upgrade path for 3V systems while retaining full software and hardware compatibility with DS1285-based designs.
BQ3285LSS Specifications
- Product attributes
- Attribute value
- Manufacturer:
- Texas Instruments
- Series:
- -
- Package/Case:
- 24-SSOP (0.154", 3.90mm Width)
- Packaging:
- Tube
- Product Status:
- Obsolete
- Programmable:
- Not Verified
- Type:
- Clock/Calendar
- Features:
- Alarm, Daylight Savings, Leap Year, NVSRAM, Square Wave Output
- Memory Size:
- 242B
- Time Format:
- HH:MM:SS (12/24 hr)
- Date Format:
- YY-MM-DD-dd
- Interface:
- Parallel
- Voltage - Supply:
- 2.7V ~ 3.6V
- Voltage - Supply, Battery:
- 2.4V ~ 4V
- Current - Timekeeping (Max):
- -
- Operating Temperature:
- -
- Mounting Type:
- Surface Mount
- Grade:
- -
- Qualification:
- -
- Supplier Device Package:
- 24-SSOP
BQ3285LSS FAQ
1.How can I place an order for BQ3285LSS through Aetrix?
Please submit a Request for Quotation (RFQ) for BQ3285LSS on Aetrix. Our sales agent will provide a competitive quotation and guide you through the order confirmation once you accept the terms.
2.Are the price and stock information for BQ3285LSS reliable?
The price and inventory of BQ3285LSS are updated periodically and may fluctuate due to market conditions. Stock and pricing data are typically refreshed every 24 hours. Quotation validity for BQ3285LSS is usually 5 days.
3.What payment methods are accepted for BQ3285LSS?
We accept Wire Transfer, PayPal, Credit Card, Western Union, MoneyGram, and Escrow for BQ3285LSS transactions.
Note: Certain payment methods may incur a processing fee.
4.How is shipping managed for BQ3285LSS?
BQ3285LSS orders can be shipped via leading logistics carriers, including DHL, UPS, FedEx, TNT, or Registered Mail.
Once your BQ3285LSS order is processed, you will receive an email with the shipment details and tracking number.
Note: Tracking information may take up to 24 hours to appear. Express delivery typically takes 3–5 business days.
5.How can I obtain technical support or documentation for BQ3285LSS?
For technical support, including BQ3285LSS datasheets, pinout diagrams, or application guidance, please contact our engineering support team. They can provide detailed documentation and assistance for your BQ3285LSS requirements.
6.How does Aetrix verify that BQ3285LSS is sourced from the original manufacturer or authorized distributors?
All BQ3285LSS products on Aetrix are procured from qualified distributors and authorized channels. Our dedicated quality assurance team conducts strict verification, including traceability checks and, if necessary, third-party testing. This ensures that BQ3285LSS meets industry standards.
7.What is the process for return or replacement of BQ3285LSS?
All BQ3285LSS units undergo pre-shipment inspection (PSI). If there is an issue with BQ3285LSS, returns or replacements are accepted under the following conditions:
1.Quantity discrepancies, incorrect items, or visible external defects (such as breakage or corrosion), acknowledged by Aetrix.
2.The issue is reported within 90 days of delivery.
3.The BQ3285LSS part is unused and in its original packaging.
Return procedure for BQ3285LSS:
1.Submit a request within 90 days.
2.Obtain a Return Material Authorization (RMA) from Aetrix.
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