1. Overview

️· What it is: The ELM440 is an integrated circuit (IC) designed to generate precise 60Hz and 1Hz output signals. It can operate either as a standalone crystal oscillator or synchronize to an external 60Hz/120Hz signal (e.g., from an AC power line).
️· Key Features:
- Dual Output: Provides both 60Hz and 1Hz signals.
- Synchronization: Can synchronize to an external 60Hz/120Hz signal, or run independently using a crystal oscillator.
- Easy Integration: Simple to use, with a few external components needed (primarily crystal loading capacitors).
- Microcontroller Core: Uses a Microchip PIC12C5XX microcontroller for its internal logic.

2. Pin Descriptions (with Key Functions)

️· Vdd (Pin 1): Positive supply voltage. Crucial for power and the power-on reset sequence.
️· XT1 & XT2 (Pins 2 & 3): Connections for the crystal oscillator. Requires external capacitors (typically 27pF) for proper operation.
️· Reset (Pin 4): Can be used to manually reset the IC. Pulled up internally.
️· Sync (Pin 5): External synchronization input. Connect to a 60Hz or 120Hz signal to synchronize the 60Hz output.
️· 1Hz (Pin 6): Output signal at 1Hz.
️· 60Hz (Pin 7): Output signal at 60Hz.
️· Vss (Pin 8): Ground connection.

3. Electrical Characteristics & Ratings

️· Supply Voltage (Vdd): 3.0V to 5.5V
️· Crystal Frequency: Designed for a 3.579545 MHz crystal (typical for NTSC colorburst signals).
️· Input Current: Relatively low, but important for power consumption calculations.
️· Output Voltage Levels: Defined by the supply voltage.

4. Operating Modes

️· Standalone Mode (Crystal Oscillator):
- Connect a crystal between XT1 and XT2.
- Add 27pF capacitors between each crystal pin and ground.
- The IC will generate a stable 60Hz output.
️· Synchronized Mode:
- Connect the Sync (Pin 5) to a 60Hz or 120Hz signal source.
- The 60Hz output will follow the frequency of the Sync signal.

5. Example Applications and Considerations

️· Timekeeping/Clock Generation: The 1Hz output is ideal for driving clock displays or generating timing signals.
️· AC Line Synchronization: The ability to synchronize to the AC power line can be useful for timing applications related to grid frequency.
️· Rectifier Circuits: When using AC line synchronization, ensure that the rectifier circuit has a large resistor (470KΩ) connected to the Sync input to prevent voltage floating.
️· Frequency Trimming: For increased accuracy, replace fixed capacitors with variable capacitors, and fine-tune.

6. Ordering Information

️· ELM440P: 300-mil Plastic DIP package
️· ELM440SM: 200-mil SOIC surface mount package