Infineon BSS84PW P-Channel Logic Level MOSFET: Datasheet, Application Circuit, and Pinout Guide
The Infineon BSS84PW is a popular P-Channel Enhancement Mode MOSFET designed specifically for low-voltage, logic-level applications. Its combination of a small SOT-323 package, good switching performance, and low threshold voltage makes it an ideal choice for a wide array of power management tasks in portable and space-constrained electronic devices.
This MOSFET is engineered to be driven directly from microcontrollers, logic ICs, and other low-voltage sources (typically 3.3V or 5V), simplifying circuit design by often eliminating the need for additional driver stages. Its primary uses include load switching, power management, DC-DC conversion, and signal switching.
Pinout Guide
The BSS84PW comes in a compact SOT-323 surface-mount package. The pinout, when viewed from the front (with the marked side facing you), is:
Pin 1 (Gate): This is the control pin. Applying a voltage relative to the Source turns the MOSFET on or off.
Pin 2 (Source): This pin is typically connected to the higher voltage rail. For a P-Channel MOSFET, the current flows from the Source to the Drain.
Pin 3 (Drain): The load is connected between this pin and ground. When the MOSFET is on, current flows into the Drain.
Key Datasheet Specifications
Understanding the absolute maximum ratings and electrical characteristics is crucial for a reliable design:
Drain-Source Voltage (VDS): -50 V
Continuous Drain Current (ID): -130 mA
Gate-Source Voltage (VGS): ±12 V
On-Resistance (RDS(on)): Typically 6.5 Ω at VGS = -4.5 V, ID = -50 mA. This low resistance minimizes power loss and voltage drop when the switch is on.
Gate Threshold Voltage (VGS(th)): Between -0.8 V and -2.5 V. This guaranteed low threshold is what qualifies it as a logic-level MOSFET, ensuring it can be fully turned on with a 3.3V or 5V signal.
Typical Application Circuit: High-Side Switch
The most common use for a P-Channel MOSFET like the BSS84PW is as a high-side switch. This configuration allows a microcontroller to control power to a load connected to ground.
Components:
MCU: Any 3.3V or 5V microcontroller (e.g., Arduino, ESP32).
Rpull-up: A resistor (e.g., 10kΩ to 100kΩ) connected from the Source to the Gate.
Rgate: A small series resistor (e.g., 100Ω) connected to the MCU pin.
Load: The device to be controlled (e.g., LED, sensor, motor driver IC).
How it Works:
1. Default OFF State: When the MCU pin is set to a high-impedance input mode or is HIGH, the pull-up resistor Rpull-up holds the Gate voltage equal to the Source voltage (V+). Since VGS = 0 V, the MOSFET is off, and no current flows to the load.
2. Turning ON: To turn the load on, the MCU pin is set to output a LOW (0V) signal. This pulls the Gate voltage down to 0V, creating a negative VGS relative to the Source (e.g., -3.3V or -5V). This voltage exceeds the threshold VGS(th), turning the MOSFET on and allowing current to flow from V+ through the MOSFET and the load to ground.
This circuit is fundamental for safely enabling and disabling power rails in battery-operated devices.
Design Considerations:
Body Diode: All MOSFETs have an intrinsic body diode. In a P-Channel, it is oriented between the Drain and Source with the anode at the Source. This means the MOSFET cannot block reverse current from Drain to Source.
Gate Protection: Although the BSS84PW has a Zener-protected gate, a small series resistor (Rgate) is still recommended to dampen any ringing and limit current spikes from the MCU pin.
Switching Speed: For very high-speed switching, careful PCB layout to minimize parasitic inductance and capacitance is necessary.
ICGOODFIND Summary
The Infineon BSS84PW is a highly efficient and compact P-Channel logic-level MOSFET that excels in low-power switching applications. Its ability to be driven directly from microcontroller GPIO pins, coupled with its low on-resistance and small form factor, makes it an exceptional component for designers looking to manage power in modern electronic products, from IoT gadgets to consumer electronics. Always consult the latest official datasheet from Infineon for final design and validation.
Keywords: Logic Level MOSFET, P-Channel, High-Side Switch, Load Switching, SOT-323.
