onsemi FDN358P P-Channel MOSFET: Datasheet, Application Circuit, and Pinout Guide

The FDN358P from onsemi is a popular P-Channel enhancement mode MOSFET housed in a compact SOT-23 surface-mount package. Renowned for its high efficiency and small form factor, this transistor is a fundamental component in a vast array of modern electronics, particularly where power management and load switching are critical. This guide provides a detailed look into its datasheet, a typical application circuit, and its pin configuration.

Datasheet Overview and Key Specifications

The FDN358P's datasheet outlines the electrical characteristics and absolute maximum ratings that define its operational limits. Key parameters include:

Drain-Source Voltage (V_DS): -20V. This specifies the maximum voltage that can be applied between the drain and source when the device is off.

Continuous Drain Current (I_D): -2.3A. The maximum continuous current it can handle.

On-Resistance (R_DS(on)): A crucial parameter for efficiency, it is typically 70mΩ at V_GS = -4.5V and 95mΩ at V_GS = -2.5V. This low on-resistance minimizes power loss and heat generation when the MOSFET is fully turned on.

Gate Threshold Voltage (V_GS(th)): Typically between -0.7V and -1.3V, this is the voltage required at the gate to start the conduction process.

These specs make the FDN358P ideal for low-voltage applications such as power distribution in portable devices, battery management systems, and DC-DC converters.

Pinout Guide

The FDN358P comes in a 3-pin SOT-23 package. The pinout, when viewed with the flat side facing you, is as follows:

Pin 1 (Left): Gate. This pin controls the conductivity between the source and drain. A voltage must be applied relative to the source to turn the device on.

Pin 2 (Middle): Source. This is the terminal through which charge carriers enter the channel. For a P-Channel MOSFET, this is typically connected to the positive supply voltage.

Pin 3 (Right): Drain. This is the terminal through which charge carriers exit the channel. The load is usually connected between the drain and ground.

Application Circuit: High-Side Load Switch

A quintessential use case for the FDN358P is a high-side switch. In this configuration, the MOSFET is placed between the positive power supply (V⁺) and the positive terminal of the load. The other side of the load is connected to ground.

How it works:

1. To turn the load ON, the gate must be pulled low relative to the source. Since the source is connected to V⁺ (e.g., 5V or 3.3V), applying a logic '0' (0V) to the gate creates the necessary negative V_GS to fully enhance the channel.

2. To turn the load OFF, the gate is pulled high to the same voltage as the source (V⁺). This brings V_GS to 0V, shutting off the channel and stopping current flow to the load.

A pull-up resistor (e.g., 10kΩ to 100kΩ) is often used from the gate to the source to ensure the MOSFET remains off if the control signal is in a high-impedance state. A series resistor (e.g., 10Ω to 100Ω) is also commonly added in line with the gate to dampen any ringing and prevent oscillations.

ICGOODFIND

The onsemi FDN358P stands out as an exceptionally efficient and compact solution for power switching tasks. Its low on-resistance and high current handling capability in a tiny SOT-23 package make it a superior choice for space-constrained designs demanding robust performance. Understanding its pinout and integrating it into a high-side switch circuit allows designers to effectively manage power in a wide range of electronic products.

Keywords:

P-Channel MOSFET

Load Switch

Power Management

SOT-23

Low On-Resistance