BQ4845S-A4N - Parallel RTC with CPU Supervisor | Texas Instruments
MPN: BQ4845S-A4N ✗ End of Life| Qty | Unit Price | Extended |
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| 1 | $0 | $0.00 |
| 10 | $0 | $0.00 |
| 100 | $0 | $0.00 |
| 500 | $0 | $0.00 |
| 1,000 | $0 | $0.00 |
BQ4845S-A4N Overview
A real-time clock is a clock-and-calendar peripheral that maintains time independently of the system processor and continues counting during main-power loss when a backup source is present. The BQ4845 belongs to the broader hierarchy of timing ICs, real-time clocks, clock-and-calendar devices, and semiconductor system-support components. Its CPU-supervisor functions extend the role beyond timekeeping by supporting reset, watchdog, and interrupt-controlled system-management functions.
The verified manufacturer material identifies a less-than-500 nA clock-operation current in backup mode, direct support for a 32.768 kHz quartz crystal, and an on-chip battery-backup switchover circuit with nonvolatile control for external SRAM. The device also provides conditional chip-enable output CEOUT and a battery-voltage output VOUT. These features make the BQ4845S-A4N suitable for systems that need persistent timekeeping, external SRAM retention, and processor supervision in one device.
The clock/calendar registers use a parallel interface resembling standard SRAM access, allowing a host processor to read and write time and control registers while observing the required operating modes and timing. The manufacturer datasheet states that the BQ4845 has the same clock/calendar and control interface as standard SRAM. This architecture simplifies integration with processors and bus controllers, although software must handle mode selection and access timing correctly.
Typical uses include industrial control systems, data loggers, point-of-sale terminals, fax machines, copiers, computers, and embedded equipment requiring a real-time clock. A 32.768 kHz crystal provides the timebase, while the backup battery allows the RTC and associated SRAM-control function to operate when the primary supply disappears. The low backup current helps preserve standby power in unattended systems.
When laying out a design, connect the crystal and backup battery according to the manufacturer datasheet and keep the RTC bus traces short and well referenced. Confirm the device’s reset, watchdog, interrupt, and alarm configuration in software before enabling system-critical events. Because the verified data does not provide complete electrical limit values, pricing, or the full pin map, use the official BQ4845 datasheet for final schematic and timing decisions.
This product data consolidates the verified distributor identity, manufacturer function description, interface type, package information, backup-current claim, and targeted substitute information. It also distinguishes confirmed same-package candidates from unverified alternatives so engineers can validate footprint, pinout, and operating requirements before replacement.
Drop-in alternatives for BQ4845S-A4N — same package, pin-to-pin compatible. Different-package parts requiring PCB rework are excluded.
Variants in this series
Same-series models that are drop-in compatible with BQ4845S-A4N (same form factor and footprint) — differing in Package, Interface, Mounting Type, Product Type.
Quick Comparison Tool — Select alternative parts for side-by-side comparison:
BQ4845YP-A4
✅ Drop-In✓ In Stock
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View Datasheet →BQ4845YS-A4G4
✅ Drop-In📋 Reference alternative (not in catalog)
BQ4845YS-A4N
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View Datasheet →BQ4845YS-A4NTR
✅ Drop-In📋 Reference alternative (not in catalog)
BQ4845S-A4NTRG4
✅ Drop-In📋 Reference alternative (not in catalog)
BQ4845S-A4N Specifications
| Device Type | Real-time clock (RTC) with CPU supervisor |
| Timekeeping Format | Seconds through years in BCD format |
| Calendar Capability | 100-year calendar |
| Interface | Parallel SRAM-compatible clock/calendar and control interface |
| Clock Crystal Frequency | 32.768 kHz |
| Backup Battery | 3 V |
| Backup Mode Clock Current | Less than 500 nA |
| NVSRAM Control | On-chip battery-backup switchover with nonvolatile external-SRAM control |
| Supervisory Functions | CPU supervisor, watchdog timer, and microprocessor reset features |
| Programmable Interrupts | Yes |
| Alarm Support | Yes |
| Daylight Saving Time | Yes |
| Leap-Year Handling | Yes |
| Battery Low Warning | Yes |
| Package | 28-pin SOIC, 0.295 inch body width, 7.50 mm width |
| Technology | CMOS |
| Terminal Count | 28 terminals |
| Operating Temperature Range | -40 C to +85 C |
| Mounting Type | Surface mount |
| RoHS Status | unknown |
| REACH Status | unknown |
| AEC-Q100 Qualification | unknown |
BQ4845S-A4N 28-pin soic, 0.295 inch body width, 7.50 mm width Pin Configuration Guide
Pin configuration for BQ4845S-A4N (28-pin soic, 0.295 inch body width, 7.50 mm width package). Pin numbering, functions, and connection diagrams are defined in the manufacturer datasheet. Refer to it for the exact footprint and soldering guidelines.
No detailed pinout data available for BQ4845S-A4N.
Refer to the datasheet for full pin configuration.
Typical Applications
BQ4845S-A4N is suitable for 6 applications: Industrial Control Systems, Data Loggers and Environmental Recorders, Point-of-Sale Terminals, Fax Machines and Copiers, Embedded Computers and Industrial Terminals, Battery-Backup Industrial Instrumentation.
Industrial Control Systems
The BQ4845S-A4N fits industrial controllers that need continuous time-of-day tracking, calendar alarms, processor reset supervision, and data retention during power loss. Its 32.768 kHz crystal interface provides the RTC timebase, while the verified backup-mode current of less than 500 nA supports low standby consumption. The parallel SRAM-like interface can connect to an embedded processor bus, and the external-SRAM control path helps preserve operational records when system voltage disappears. The -40 C to +85 C operating range covers many industrial environments, although enclosure temperature, surge, isolation, and certification requirements still need separate system-level verification.
Recommended
Data Loggers and Environmental Recorders
A data logger can use the BQ4845S-A4N to timestamp measurements across days and years, alarm at scheduled intervals, and retain records during battery backup. The 100-year calendar and BCD timekeeping provide application-readable time information, while the 32.768 kHz crystal establishes the long-term timebase. The CPU supervisor and watchdog functions help a microcontroller recover from stalled firmware or power disturbances. For remote or unattended deployments, the less-than-500 nA backup clock-operation current is useful, but battery-life calculations must include external SRAM leakage, sensor standby current, and the backup cell’s own leakage.
Recommended
Point-of-Sale Terminals
The BQ4845S-A4N is suitable for point-of-sale equipment that must preserve transaction timestamps and maintain a real calendar through power interruptions. Its alarm, daylight-saving, leap-year, interrupt, and watchdog functions support scheduled operations and processor supervision without requiring a separate timing IC. CEOUT can help manage an external SRAM when transaction data must remain available during backup operation. The 28-pin SOIC package and parallel interface are appropriate for a controller board with adequate routing space, but the designer must verify signal timing, reset behavior, and battery fail-safe requirements in the final firmware and schematic.
Recommended
Fax Machines and Copiers
Office equipment can use the BQ4845S-A4N to retain document timestamps, scheduled service events, and system time across unexpected power loss. The RTC’s 100-year calendar and alarm support are useful for maintenance logging, while the CPU supervisor and watchdog help recover embedded controller operation after faults. The external-SRAM control function is valuable when buffered print or scan data must remain available during standby. The manufacturer specifically identifies fax machines and copiers as target applications. Keep the backup battery electrically isolated from the main rail as required by the reference design and verify all write-protection states before enabling critical print jobs.
Recommended
Embedded Computers and Industrial Terminals
The BQ4845S-A4N provides a consolidated timing and supervision block for embedded computers, terminals, and compact industrial interfaces. A processor can read and write the clock/calendar locations through the SRAM-like parallel interface, while watchdog and reset support improve recovery after firmware or bus faults. Backup operation preserves RTC state and supports external-SRAM retention when the primary supply fails. Because the supplied package information identifies a 28-pin SOIC, PCB planners should reserve routing and decoupling according to the official datasheet and verify signal levels against the host processor. The part is intended for low-power systems, not as a substitute for a high-speed digital timer.
Recommended
Battery-Backup Industrial Instrumentation
In battery-backed instrumentation, the BQ4845S-A4N helps preserve event timing and controller state when the main supply drops. The 3 V backup-battery connection, battery-backup switchover, VOUT monitoring output, and external-SRAM control support a controlled retention architecture. Its less-than-500 nA backup clock-operation current helps limit standby demand, but the complete power budget must include external memory and support circuitry. The watchdog and reset functions add supervisory value in remote installations where maintenance visits are expensive. Validate the backup-source capacity for the required outage duration and ensure the battery chemistry and protection network match the manufacturer reference design.
Recommended
Recommended Products Summary
Engineering reference data for BQ4845S-A4N — comparison, design guidance, and compliance information.
Selection Guide
Comparison with Alternatives
| Parameter | This Product | BQ4845YP-A4 | BQ4845YS-A4G4 | BQ4845YS-A4N | BQ4845YS-A4NTR | BQ4845S-A4NTRG4 |
|---|---|---|---|---|---|---|
| Brand | Texas Instruments | Texas Instruments | Texas Instruments | Texas Instruments | Texas Instruments | Texas Instruments |
| Package | 28-pin SOIC | SOIC-28; same-package candidate | SOIC-28; related family candidate | PDSO28; related family candidate | 28-pin SOIC; related family candidate | SOIC-28; related family candidate |
Key Differentiators
- Consolidates RTC and CPU-supervision functions (vs BQ4845YS-A4N)
- Verified low backup-mode clock current (vs BQ4845YP-A4)
- Direct external-SRAM retention support (vs BQ4845YS-A4N)
- Explicit same-package replacement evidence (vs BQ4845YP-A4)
Design Notes
Design the backup path around the manufacturer’s 3 V battery connection and confirm the exact VCC, VOUT, and battery-current limits from the official datasheet. The verified less-than-500 nA figure describes clock-operation current in backup mode, not total board standby current. Include external-SRAM leakage, pull networks, supervisor load, and battery self-discharge in the power budget. Use a protected battery source and verify that the main supply and backup source cannot back-drive each other outside the manufacturer’s intended operating condition.
Route the 32.768 kHz crystal connection as short as practical and follow the manufacturer’s grounding and capacitor-placement guidance. Keep the RTC timebase away from noisy switching nodes, high-current return paths, and communication edges. Place required decoupling capacitors close to the supply pins, and provide a clean ground reference for the crystal oscillator. The verified web data confirms the crystal frequency and package family but does not specify the exact layout values, so final placement must follow the BQ4845 datasheet reference layout.
Do not substitute an RTC solely because the package is called 28-pin SOIC. Confirm pin numbering, signal direction, reset polarity, watchdog timing, interrupt behavior, crystal requirements, and supply limits for the exact ordering suffix. The supplied web data specifically supports BQ4845YP-A4 as a same-package replacement candidate, while other related BQ4845YS variants are not fully characterized in the excerpts. Validate the replacement with a schematic diff, timing review, and bench power-fail test before production release.
Compliance Information
The supplied verified web data does not state RoHS, REACH, AEC-Q100, lead-free, halogen-free, or conflict-minerals status. These fields must be confirmed from the current manufacturer product documentation or supplier certificates.
