fixed-voltage monolithic integrated-circuit voltage regulators is designed for a wide range of applications # 79L08A Negative Voltage Regulator Technical Documentation
Manufacturer : STMicroelectronics
## 1. Application Scenarios
### Typical Use Cases
The 79L08A is a three-terminal negative voltage regulator that provides a fixed -8V output with up to 100mA output current. Typical applications include:
Power Supply Sections
- Negative rail generation in dual-power supply systems (±8V)
- Local regulation for analog circuits requiring negative bias
- Op-amp power supply rails in mixed-signal systems
- Audio amplifier negative voltage requirements
Signal Processing Applications
- Biasing for operational amplifiers in inverting configurations
- Reference voltage generation for analog-to-digital converters
- Sensor interface circuits requiring negative polarization
- Active filter implementations with negative supply requirements
### Industry Applications
Consumer Electronics
- Audio equipment: preamplifiers, equalizers, mixers
- Portable instruments requiring dual-supply operation
- Test and measurement equipment calibration circuits
Industrial Systems
- Process control instrumentation
- Data acquisition systems
- Industrial automation controllers
- Motor drive control circuits
Telecommunications
- RF circuit biasing
- Line interface circuits
- Signal conditioning modules
### Practical Advantages and Limitations
Advantages:
- Compact Solution : Integrated thermal shutdown and current limiting
- Stable Performance : Internal compensation ensures stability with minimal external components
- Low Dropout : Typically 1.7V maximum at full load current
- Thermal Protection : Built-in thermal overload protection prevents damage
- Short-Circuit Protection : Internal current limiting protects against output shorts
Limitations:
- Fixed Output : Cannot be adjusted (fixed -8V output)
- Current Capacity : Limited to 100mA maximum output current
- Heat Dissipation : Requires proper heatsinking at higher currents
- Input Voltage Range : Limited to -35V maximum input voltage
## 2. Design Considerations
### Common Design Pitfalls and Solutions
Thermal Management Issues
- Pitfall : Overheating when operating near maximum current without adequate heatsinking
- Solution : Calculate power dissipation (P_D = (V_IN - V_OUT) × I_OUT) and ensure junction temperature remains below 125°C
- Implementation : Use thermal vias, copper pours, or external heatsinks for currents above 50mA
Stability Problems
- Pitfall : Oscillations due to improper bypass capacitor selection
- Solution : Use 0.33μF tantalum or 1μF aluminum electrolytic capacitor at input, 0.1μF ceramic at output
- Implementation : Place bypass capacitors as close as possible to regulator pins
Load Regulation Issues
- Pitfall : Poor regulation with rapidly changing loads
- Solution : Ensure input capacitor can supply transient current demands
- Implementation : Use low-ESR capacitors and minimize trace inductance
### Compatibility Issues with Other Components
Input Source Compatibility
- Compatible with AC-DC converters, DC-DC converters, and battery sources
- Requires input voltage between -10.5V and -35V for proper regulation
- Incompatible with positive voltage sources without proper inversion
Load Circuit Considerations
- Suitable for analog and digital circuits requiring -8V supply
- May require additional filtering for noise-sensitive analog circuits
- Compatible with most op-amps, comparators, and other analog ICs
Mixed-Signal Systems
- Ensure proper grounding between digital and analog sections
- Use separate regulators for analog and digital sections when possible
- Implement star grounding to minimize ground loops
### PCB Layout Recommendations
Component Placement
- Place input and output capacitors within 10mm of regulator pins
- Position thermal relief features (vias, copper areas) adjacent to ground pin
- Keep sensitive analog circuits away from switching regulators
