LOW VOLTAGE HEX BUFFER (OPEN DRAIN) WITH 5V TOLERANT INPUTS# 74LCX07 Hex Buffer/Driver with Open-Drain Outputs Technical Documentation
## 1. Application Scenarios
### Typical Use Cases
The 74LCX07 is a hex buffer/driver featuring open-drain outputs , making it particularly suitable for several key applications:
Bus Interface Applications
- I²C and SMBus systems : The open-drain outputs are ideal for bidirectional bus applications where multiple devices share the same communication lines
- Level shifting : Converting between different voltage domains (e.g., 3.3V to 5V systems) while maintaining signal integrity
- Wired-AND configurations : Multiple outputs can be connected together to create logical AND functions without additional components
Signal Conditioning
- Waveform shaping : Cleaning up noisy digital signals while providing current drive capability
- Load driving : Capable of sinking up to 24mA per output, making it suitable for driving LEDs, relays, and other peripheral devices
- Signal isolation : Providing buffering between sensitive circuitry and higher-power loads
### Industry Applications
Consumer Electronics
- Smartphones and tablets : Level shifting between core processors and peripheral components
- Gaming consoles : Interface between different voltage domain ICs
- Home automation : Driving indicator LEDs and relay control circuits
Industrial Systems
- PLC interfaces : Signal conditioning for industrial control systems
- Motor control : Driving optoisolators and power MOSFET gates
- Sensor networks : Bus interface for distributed sensor systems
Automotive Electronics
- Infotainment systems : Level translation between different subsystem voltages
- Body control modules : Driving various automotive loads while maintaining signal integrity
### Practical Advantages and Limitations
Advantages:
- 5V tolerant inputs : Can safely interface with 5V logic while operating at lower core voltages (2.0V to 3.6V)
- Low power consumption : Typical ICC of 10μA (static) makes it suitable for battery-powered applications
- High-speed operation : Propagation delay of 3.5ns typical at 3.3V supports modern high-speed interfaces
- Bus-hold circuitry : Eliminates the need for external pull-up resistors on inputs
Limitations:
- External pull-up requirement : Open-drain outputs require external pull-up resistors for proper HIGH level output
- Limited sourcing capability : Cannot actively drive HIGH levels; relies on external pull-up networks
- Power sequencing considerations : Care required when interfacing between different voltage domains during power-up/power-down
## 2. Design Considerations
### Common Design Pitfalls and Solutions
Pull-up Resistor Selection
- Pitfall : Incorrect pull-up resistor values causing signal integrity issues
- Solution : Calculate resistor values based on:
- Desired rise time: R = t_rise / (C_bus × ln(Vdd/Vdd-0.7))
- Maximum sink current: Ensure R > (Vdd - 0.4V) / 24mA
- Typical values range from 1kΩ to 10kΩ depending on bus speed and capacitance
Power Supply Decoupling
- Pitfall : Inadequate decoupling causing signal ringing and false triggering
- Solution :
- Place 100nF ceramic capacitor within 5mm of VCC pin
- Additional 10μF bulk capacitor for systems with multiple devices
- Use multiple vias for low-impedance ground connections
Simultaneous Switching Noise
- Pitfall : Multiple outputs switching simultaneously causing ground bounce
- Solution :
- Implement proper ground plane design
- Stagger output switching in firmware when possible
- Use series termination resistors for long traces
### Compatibility Issues with Other Components
Mixed Voltage Systems
- 3.3
