Real-Time Clock RTC Module# BQ3287EMT Technical Documentation
## 1. Application Scenarios
### Typical Use Cases
The BQ3287EMT is a real-time clock (RTC) with integrated battery-backed SRAM , primarily designed for system timekeeping and data retention applications. Key use cases include:
- Server and workstation motherboards requiring accurate timekeeping during power cycles
- Industrial automation systems needing persistent configuration storage
- Medical equipment requiring reliable time-stamped data logging
- Network infrastructure devices maintaining synchronization during power loss
- Point-of-sale systems preserving transaction data during power interruptions
### Industry Applications
- Enterprise Computing : Server racks, data center equipment, and high-availability systems
- Industrial Control : PLCs, SCADA systems, and process control equipment
- Telecommunications : Network switches, routers, and base station controllers
- Medical Devices : Patient monitoring systems and diagnostic equipment
- Automotive : Infotainment systems and telematics units (non-safety critical)
### Practical Advantages
- Integrated Solution : Combines RTC, calendar, and 256-byte non-volatile RAM
- Battery Backup : Maintains timekeeping and RAM data for over 10 years
- Low Power Consumption : Typical backup current of <1μA
- Wide Temperature Range : Operates from -40°C to +85°C
- Automatic Leap Year Compensation : Accurate calendar through 2100
### Limitations
- Limited RAM Capacity : 256 bytes may be insufficient for large data sets
- Battery Dependency : Requires external battery for backup functionality
- Interface Speed : I²C interface limits data transfer rates
- No On-chip Oscillator : Requires external 32.768kHz crystal
## 2. Design Considerations
### Common Design Pitfalls and Solutions
Power Supply Sequencing
- Pitfall : Improper power-up sequencing causing data corruption
- Solution : Implement proper power monitoring and ensure VCC stabilizes before accessing RTC
Battery Backup Issues
- Pitfall : Battery voltage drop during high current events
- Solution : Include decoupling capacitors near battery input and limit battery current
Crystal Oscillator Problems
- Pitfall : Incorrect crystal loading capacitors causing frequency drift
- Solution : Use specified 12.5pF load crystals and follow manufacturer recommendations
### Compatibility Issues
Microcontroller Interfaces
- I²C Compatibility : Works with standard I²C interfaces (100kHz/400kHz)
- Voltage Levels : 3.3V operation compatible with most modern microcontrollers
- Pull-up Requirements : Requires external I²C pull-up resistors (typically 4.7kΩ)
Power Management Integration
- Backup Switching : Compatible with most power management ICs
- Battery Types : Supports standard 3V lithium coin cells (CR2032, etc.)
- System Reset : Integrates with system reset circuits for proper initialization
### PCB Layout Recommendations
Crystal Placement
- Place crystal within 10mm of X1 and X2 pins
- Use ground plane under crystal circuit
- Keep crystal traces short and symmetrical
- Avoid routing other signals near crystal traces
Power Supply Decoupling
- Place 100nF ceramic capacitor within 5mm of VCC pin
- Use 1μF tantalum capacitor for bulk decoupling
- Implement separate decoupling for battery input
Signal Routing
- Route I²C signals as differential pair when possible
- Keep SDA and SCL traces equal length
- Minimize trace lengths to reduce noise susceptibility
- Use vias sparingly in critical signal paths
Grounding Strategy
- Use solid ground plane beneath component
- Connect all ground pins directly to
