Professional IC Distribution & Technical Solutions

The MK48T87B-24 is a real-time clock (RTC) and NVRAM (Non-Volatile RAM) integrated circuit manufactured by STMicroelectronics (ST).

Key Specifications:

• Memory: 8KB of non-volatile SRAM
• RTC Functionality:
• Seconds, minutes, hours, day, date, month, year (with leap year compensation up to 2100)
• 12-hour or 24-hour time format
• Automatic daylight saving time adjustment
• Supply Voltage: 4.5V to 5.5V
• Operating Temperature Range: 0°C to +70°C
• Clock Accuracy: ±2 minutes per month at 25°C
• Battery Backup: Integrated lithium energy source (retains data for at least 10 years)
• Interface: Parallel (8-bit)
• Package: 28-pin DIP (Dual In-line Package)

Features:

• Non-Volatile Storage: Maintains data without external power
• Battery-Backed SRAM: Ensures continuous operation during power loss
• Low Power Consumption: Optimized for battery backup
• Industrial-Grade Reliability: Suitable for embedded systems

Applications:

• Embedded systems
• Industrial controls
• Point-of-sale (POS) terminals
• Medical equipment
• Data logging

This device is designed for applications requiring reliable timekeeping and non-volatile memory storage.

# Technical Analysis of the MK48T87B-24 Timekeeping RAM

## Practical Application Scenarios

The MK48T87B-24, manufactured by ST, is a non-volatile timekeeping RAM (NVSRAM) that integrates a real-time clock (RTC) with a static RAM (SRAM). This component is widely used in applications requiring persistent timekeeping and data retention during power loss.

Industrial Automation Systems

In industrial environments, the MK48T87B-24 ensures accurate timestamping for event logging, process synchronization, and fault diagnostics. Its non-volatile nature prevents data loss during power interruptions, making it ideal for PLCs (Programmable Logic Controllers) and SCADA systems.

Embedded Computing

Embedded systems, such as point-of-sale (POS) terminals and medical devices, rely on the MK48T87B-24 for maintaining real-time clock data and critical configuration settings. The integrated battery backup ensures continuous operation even during power cycling.

Telecommunications Equipment

Network switches and routers use the MK48T87B-24 to log system events with precise timestamps, aiding in debugging and compliance with regulatory standards. The SRAM’s fast access time supports high-performance data handling.

## Common Design-Phase Pitfalls and Avoidance Strategies

Incorrect Battery Backup Implementation

A frequent mistake is improper battery selection or connection, leading to premature failure or data corruption.

Solution: Use a lithium battery (e.g., BR1225) with a suitable holder and ensure correct polarity. Verify the battery’s voltage range (2.5V–3.5V) matches the device requirements.

Clock Accuracy Drift

Temperature fluctuations and poor PCB layout can degrade RTC accuracy.

Solution: Place the MK48T87B-24 away from heat sources and use a crystal oscillator with low ppm tolerance. Follow manufacturer guidelines for trace routing to minimize noise.

SRAM Write Timing Violations

Exceeding access time specifications during high-speed writes can corrupt data.

Solution: Adhere to the 150ns access time (for -24 speed grade) and implement proper bus contention management in multi-master systems.

## Key Technical Considerations for Implementation

Power Supply Decoupling

Ensure stable operation by placing 0.1µF decoupling capacitors near the VCC pin. A bulk capacitor (10µF) is recommended for handling transient loads during power transitions.

I2C Interface Compliance

The MK48T87B-24 supports I2C communication. Verify pull-up resistor values (typically 4.7kΩ) and ensure the host controller’s clock speed does not exceed 400kHz.

Battery Backup Circuitry

Design the power switchover circuit to prioritize main power and seamlessly transition to battery backup during outages. Schottky diodes or MOSFET-based switches are commonly used for low-voltage drop.

By addressing these considerations, designers can maximize the reliability and performance of the MK48T87B-24 in time-critical and data-sensitive applications.