Infineon BSS138NH6327: Key Specifications and Application Circuit Design

The Infineon BSS138NH6327 is a widely adopted N-channel logic level enhancement mode MOSFET, renowned for its compactness and efficiency in low-voltage applications. Housed in a space-saving SOT-23 (TO-236AB) package, this MOSFET is engineered to deliver robust performance with minimal power loss, making it a cornerstone component in modern electronic design.

Key Specifications

The defining characteristics of the BSS138NH6327 are its low threshold voltage (V_GS(th)) and low on-state resistance (R_DS(on)). These parameters are crucial for operation in circuits controlled by microcontrollers (MCUs) and other low-power logic circuits.

Drain-Source Voltage (V_DS): 50 V – Suitable for a broad range of low-power applications.

Continuous Drain Current (I_D): 220 mA at T_amb = 25°C – Adequate for driving small motors, LEDs, relays, and other peripheral devices.

On-State Resistance (R_DS(on)): 3.5 Ω max at V_GS = 4.5 V, I_D = 50 mA – This low resistance minimizes voltage drop and power dissipation across the switch when fully turned on, enhancing overall circuit efficiency.

Gate Threshold Voltage (V_GS(th)): 0.5 V to 1.5 V – A truly logic-level compatible gate. It can be driven directly from 3.3 V or 5 V microcontroller GPIO pins without requiring a level shifter or additional gate driver circuitry.

Package: SOT-23-3 – The ultra-small footprint is ideal for high-density PCB designs.

Application Circuit Design: MCU Interface for Load Switching

A fundamental and common application is using the MOSFET as a switch controlled by a microcontroller. The circuit diagram below illustrates a standard configuration for driving a load, such as a string of LEDs or a small DC motor.

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[Simple Circuit Diagram]

Vcc (Load Power) --- Load (e.g., LED with resistor) --- Drain (D)

|

Source (S) --- Ground

|

Microcontroller GPIO --- Resistor (R_g) --- Gate (G)

|

Zener Diode (Optional) --- Ground

```

Design Considerations and Component Selection:

1. Gate Resistor (R_g): A series resistor (typically between 10 Ω to 100 Ω) is placed between the MCU's GPIO pin and the MOSFET's gate. This resistor limits the inrush current during switching, dampens ringing caused by parasitic inductance, and protects the MCU pin from potential voltage spikes.

2. Pull-Down Resistor: A high-value resistor (e.g., 10 kΩ to 100 kΩ) connected from the gate to ground is often recommended. It ensures the MOSFET remains definitely off when the GPIO pin is in a high-impedance state (e.g., during MCU reset or startup), preventing false triggering.

3. Freewheeling Diode (for Inductive Loads): When switching inductive loads like relays or motors, a flyback or freewheeling diode must be connected in reverse bias across the load. This provides a safe path for the inductive kickback current when the MOSFET turns off, protecting the MOSFET from damage due to voltage spikes exceeding its V_DS rating.

4. Gate Protection (Optional): In electrically noisy environments, a low-capacitance Zener diode (e.g., 5.6V) placed between the gate and source can clamp any transient voltages that exceed the maximum V_GS rating (±12 V for the BSS138), adding a layer of protection.

Operation: When the microcontroller outputs a logic 'HIGH' (3.3V or 5V), the MOSFET's gate is charged above its threshold voltage, turning the device on. This creates a low-resistance path between drain and source, allowing current to flow through the load to ground. A logic 'LOW' from the MCU discharges the gate, turning the MOSFET off and cutting power to the load.

ICGOODFIND

The Infineon BSS138NH6327 stands out as an exceptionally versatile and efficient solution for low-power switching tasks. Its combination of logic-level compatibility, low R_DS(on), and a miniature package makes it an indispensable component for designers working on portable devices, IoT modules, and any application where space and power efficiency are paramount. Proper circuit design, including gate driving and protection for inductive loads, is key to unlocking its full potential and ensuring long-term reliability.

Keywords:

1. Logic-Level MOSFET

2. Low R_DS(on)

3. SOT-23 Package

4. Application Circuit Design

5. Load Switching