BSS119NH6327: Key Specifications and Application Circuit Design
The BSS119NH6327 is a popular N-channel enhancement mode MOSFET from Infineon Technologies, designed primarily for low-voltage, low-power switching applications. Its combination of a low threshold voltage, high efficiency, and compact package makes it a versatile choice for designers in consumer electronics, power management, and signal switching.
Key Electrical Specifications
Understanding the core electrical parameters is crucial for effective circuit design. The BSS119NH6327 stands out with the following specifications:
Drain-Source Voltage (VDS): 180 V. This defines the maximum voltage the device can block between drain and source in the off-state.
Continuous Drain Current (ID): 130 mA. This is the maximum continuous current it can handle in the on-state.
On-Resistance (RDS(on)): 10.5 Ω (max. at VGS = 10 V, ID = 50 mA). A low RDS(on) is critical for minimizing conduction losses and improving efficiency.
Gate-Source Threshold Voltage (VGS(th)): 1.5 - 3 V (typical). This low threshold voltage allows it to be easily driven by low-voltage logic (e.g., 3.3V or 5V) from microcontrollers and logic ICs.
Package: The device is housed in a SOT-23 surface-mount package, which is ideal for space-constrained PCB designs.
Application Circuit Design: A Low-Side Switch
One of the most common applications for the BSS119NH6327 is as a low-side switch to control a load, such as a relay, LED, or small motor. The circuit diagram and design considerations are as follows.
Circuit Operation:
1. When the microcontroller's GPIO pin outputs a logic HIGH (3.3V or 5V), which is greater than the MOSFET's VGS(th), the transistor turns on.
2. Current flows from the positive supply (VDD), through the load, through the MOSFET, and to ground, thus activating the load.
3. When the GPIO outputs a logic LOW (0V), the MOSFET turns off, interrupting the current path and turning off the load.
Critical Design Considerations:
1. Gate Driver: Since the MOSFET can be driven directly by logic levels, a dedicated driver IC is often unnecessary. However, a gate resistor (RG) of around 10Ω to 100Ω is recommended to dampen any ringing and suppress high-frequency oscillations caused by parasitic inductance.
2. Flyback Diode (D1): When driving an inductive load like a relay or motor, a flyback diode is absolutely essential. This diode provides a safe path for the inductive kickback current when the MOSFET turns off, protecting it from damage due to voltage spikes that can exceed its VDS rating.
3. Pull-Down Resistor (RPD): A high-value resistor (e.g., 10kΩ to 100kΩ) connected between the gate and ground is vital. It ensures the MOSFET remains firmly off when the microcontroller pin is in a high-impedance state (e.g., during boot-up or reset), preventing false triggering.
The BSS119NH6327 is an excellent choice for designers seeking a robust, logic-level MOSFET for low-power switching tasks. Its high voltage rating and low threshold voltage make it particularly suited for interfacing between modern microcontrollers and various loads in applications like smart home devices, automotive modules, and portable electronics. Careful attention to the inclusion of a flyback diode for inductive loads is the key to a reliable and long-lasting design.
Keywords: Logic-Level MOSFET, Low-Side Switch, Application Circuit, SOT-23, Flyback Diode
