CMOS, 3 ohm Low Voltage 4-/8-Channel Multiplexers# ADG708CRU Technical Documentation
## 1. Application Scenarios
### Typical Use Cases
The ADG708CRU is an 8-channel CMOS analog multiplexer designed for precision signal routing applications. Typical use cases include:
Signal Routing Systems
- Multi-channel data acquisition systems : Enables sequential sampling of multiple analog sensors (temperature, pressure, strain gauges) through a single ADC
- Automated test equipment : Routes test signals to multiple device-under-test (DUT) channels
- Medical instrumentation : Switches between different bio-potential electrodes or sensor inputs
Communication Systems
- Base station antenna switching : Selects between multiple antenna elements
- Signal chain configuration : Reconfigures filter paths or gain stages in programmable instruments
- Battery monitoring systems : Sequences voltage measurements across multiple battery cells
### Industry Applications
Industrial Automation
- PLC I/O expansion modules
- Process control system signal conditioning
- Motor control feedback loop switching
Telecommunications
- RF front-end signal routing
- Baseband processing path selection
- Network analyzer channel switching
Medical Electronics
- Patient monitoring equipment
- Diagnostic imaging systems
- Portable medical devices
Automotive Systems
- Battery management systems (BMS)
- Sensor interface modules
- Infotainment system input selection
### Practical Advantages and Limitations
Advantages:
- Low power consumption : Typical supply current of 0.01 μA in shutdown mode
- High integration : 8:1 multiplexing in compact TSSOP-16 package
- Excellent signal integrity : <0.5 Ω on-resistance matching between channels
- Wide voltage range : Single supply operation from 1.8V to 5.5V
- Fast switching : 30 ns typical transition time
Limitations:
- Channel-to-channel crosstalk : -90 dB at 1 MHz limits high-frequency performance
- On-resistance variation : ±0.25 Ω variation with signal voltage changes
- Charge injection : 5 pC typical may affect precision sampling circuits
- Maximum signal range : Limited to supply rails, not suitable for high-voltage applications
## 2. Design Considerations
### Common Design Pitfalls and Solutions
Power Supply Sequencing
- Pitfall : Applying analog signals before VDD can cause latch-up or damage
- Solution : Implement power-on reset circuit or ensure VDD stabilizes before signal application
Signal Integrity Issues
- Pitfall : Excessive parasitic capacitance degrading high-frequency performance
- Solution : Keep trace lengths short and use proper impedance matching for frequencies >10 MHz
Thermal Management
- Pitfall : Continuous current >30 mA causing excessive self-heating and parameter drift
- Solution : Implement current limiting or use external buffer for high-current applications
### Compatibility Issues with Other Components
ADC Interface Considerations
- Issue : Multiplexer settling time may exceed ADC acquisition window
- Resolution : Allow adequate settling time (typically 200-500 ns) before ADC conversion start
Digital Control Interface
- Issue : Logic level mismatch with 1.8V/3.3V microcontrollers
- Resolution : Ensure VDD matches digital logic levels or use level translation
Amplifier Loading
- Issue : Multiplexer capacitance (35 pF typical) can cause op-amp instability
- Resolution : Use amplifiers with adequate phase margin or add series isolation resistors
### PCB Layout Recommendations
Power Supply Decoupling
- Place 100 nF ceramic capacitor within 5 mm of VDD pin
- Add 10 μF bulk capacitor for systems with dynamic current demands
- Use separate ground returns for digital and analog sections
Signal Routing
- Route analog signals as differential pairs where possible
- Maintain 3W spacing rule between
