Professional IC Distribution & Technical Solutions

The DS1672S-33+ is a real-time clock (RTC) with an integrated trickle charger, manufactured by DALLAS (now part of Maxim Integrated).

Key Specifications:

• Supply Voltage: 3.3V (operating range: 3.0V to 3.6V)
• Timekeeping Current: 500nA (typical)
• Clock Accuracy: ±2 minutes per month at 25°C
• Battery Backup Input: Supports external battery or supercapacitor
• Trickle Charger: Automatically charges a backup capacitor
• Interface: I²C-compatible (2-wire serial communication)
• Operating Temperature Range: -40°C to +85°C
• Package: 8-pin SOIC

Descriptions:

The DS1672S-33+ is a low-power RTC with non-volatile timekeeping functionality. It includes a built-in trickle charger to maintain a backup power source (supercapacitor or battery). The device provides seconds, minutes, hours, day, date, month, and year information with automatic leap-year compensation.

Features:

• Battery Backup Support: Maintains timekeeping during power loss
• Low Power Consumption: Minimal battery drain in backup mode
• Automatic Leap-Year Compensation: Valid up to 2100
• I²C Interface: Allows easy integration with microcontrollers
• Programmable Trickle Charger: Adjustable for different backup capacitors
• Power-Fail Detection: Monitors VCC and switches to backup power

The DS1672S-33+ is commonly used in embedded systems, data loggers, and industrial applications requiring accurate timekeeping with low power consumption.

# DS1672S-33+ Technical Analysis

## Practical Application Scenarios

The DS1672S-33+ from Dallas is a real-time clock (RTC) with an integrated trickle charger, designed for low-power applications requiring accurate timekeeping. Its primary use cases include:

1. Embedded Systems: The DS1672S-33+ is widely deployed in microcontroller-based systems where time-stamping or scheduling is critical. Examples include data loggers, industrial automation controllers, and medical devices. Its low power consumption (typically 500nA in battery backup mode) makes it ideal for battery-operated designs.

2. Consumer Electronics: Devices such as digital thermostats, smart meters, and home automation systems leverage the DS1672S-33+ for maintaining time during power outages. The integrated trickle charger ensures continuous operation by maintaining the backup battery.

3. Automotive Systems: In automotive telematics and infotainment systems, the DS1672S-33+ provides reliable timekeeping, even when the vehicle’s main power is off. Its operating temperature range (-40°C to +85°C) suits harsh environments.

4. IoT Edge Devices: For IoT applications, the RTC ensures accurate time synchronization for sensor data, which is crucial for event correlation and compliance with time-sensitive protocols.

## Common Design-Phase Pitfalls and Avoidance Strategies

1. Incorrect Backup Battery Selection:

• Pitfall: Using a non-rechargeable battery with the trickle charger can lead to leakage or failure.
• Solution: Select a rechargeable NiMH or lithium battery and verify compatibility with the trickle charger’s voltage (3.3V).

2. Improper PCB Layout:

• Pitfall: Long traces between the RTC and microcontroller increase noise susceptibility, causing timekeeping errors.
• Solution: Place the DS1672S-33+ close to the host MCU and use short, direct traces for I²C lines. Add decoupling capacitors near the VCC pin.

3. I²C Communication Issues:

• Pitfall: Unterminated I²C lines or excessive bus capacitance can lead to signal integrity problems.
• Solution: Ensure proper pull-up resistors (typically 4.7kΩ) and minimize bus capacitance by avoiding long daisy-chained connections.

4. Power Supply Sequencing:

• Pitfall: Uncontrolled power-up/down sequences may corrupt RTC registers.
• Solution: Implement a power supervisor circuit to ensure stable VCC before enabling I²C communication.

## Key Technical Considerations for Implementation

1. Clock Accuracy: The DS1672S-33+ relies on an external 32.768kHz crystal. Select a crystal with low ppm tolerance (±20ppm or better) for long-term accuracy.

2. Trickle Charger Configuration: Program the trickle charger’s enable register carefully to avoid overcharging the backup battery. Follow Dallas’s recommended settings for diode and resistor selection.

3. Software Initialization: Ensure the RTC is properly initialized on startup by writing to its control registers (e.g., enabling the oscillator and setting the time/date).

4. ESD Protection: The DS1672S-33