TRIPLE SURFACE MOUNT ZENER DIODE ARRAY # Technical Datasheet: BZX84C20TS Zener Diode
## 1. Application Scenarios
### Typical Use Cases
The BZX84C20TS is a 20V, 350mW surface-mount Zener diode in an SOT-23 package, primarily employed for voltage regulation and protection in low-power electronic circuits. Its compact size and standardized footprint make it suitable for space-constrained applications.
Primary Functions:
- Voltage Clamping: Limits voltage spikes to protect sensitive ICs (e.g., microcontroller I/O pins, sensor inputs) from electrostatic discharge (ESD) or transient overvoltage events.
- Voltage Reference: Provides a stable 20V reference for analog circuits, bias networks, or low-current regulator feedback loops.
- Signal Conditioning: Clips or limits AC signal amplitudes in audio or communication paths.
- Basic Voltage Regulation: Acts as a shunt regulator for very low-current loads (<17.5mA theoretical maximum, derated for temperature).
### Industry Applications
- Consumer Electronics: Overvoltage protection in USB ports, HDMI lines, and battery management systems (BMS) for portable devices.
- Automotive Electronics: Protection of low-voltage CAN bus lines, sensor interfaces, and infotainment systems (within specified temperature ranges).
- Industrial Control: Signal isolation barriers, PLC I/O module protection, and power supply crowbar circuits.
- Telecommunications: Surge protection on low-speed data lines and power conditioning for RF modules.
- IoT/Wearable Devices: Voltage stabilization for microcontrollers and wireless chipsets in compact form factors.
### Practical Advantages and Limitations
Advantages:
- Small Form Factor: SOT-23 package (2.9mm x 1.3mm) saves PCB real estate.
- Low Leakage Current: Typically <100nA at voltages below the Zener knee, minimizing power loss in standby.
- Fast Response Time: Reacts to transients in nanoseconds, offering effective ESD protection.
- Cost-Effective: Inexpensive solution for basic voltage regulation and protection needs.
- Standardized Footprint: Compatible with automated pick-and-place assembly.
Limitations:
- Limited Power Dissipation: 350mW maximum (derated above 25°C ambient). For a 20V Zener, this limits the maximum steady-state current to approximately 17.5mA at 25°C.
- Tolerance: Typical tolerance is ±5%, making it unsuitable for precision reference applications without calibration.
- Temperature Coefficient: The Zener voltage (`Vz`) varies with temperature (approx. +9mV/°C for 20V). This can cause drift in temperature-variable environments.
- Dynamic Impedance: Not a perfect voltage source; `Vz` changes slightly with current (`Zzt` is typically 40Ω at `Izt`). This can affect regulation accuracy under varying load conditions.
- Noise: Zener diodes generate broadband electrical noise, which may interfere with sensitive analog circuits.
## 2. Design Considerations
### Common Design Pitfalls and Solutions
1. Pitfall: Thermal Runaway
* Cause: Operating near maximum power without adequate heatsinking or consideration for ambient temperature rise.
* Solution: Derate power dissipation. At 70°C ambient, the maximum power may be only ~200mW. Use the formula: `P_max_derated = P_max * [(T_j_max - T_ambient) / (T_j_max - 25)]`. For transient suppression, select a diode with a higher power rating or use a TVS diode.
2. Pitfall: Poor Regulation Under Load
* Cause: Using the Zener with a load current that varies significantly, combined with
