onsemi FDS6673BZ P-Channel MOSFET: Datasheet, Application Circuit, and Replacement Guide

The onsemi FDS6673BZ is a popular P-Channel Power MOSFET engineered using the advanced TrenchFET® process technology. It is designed for high-efficiency power management applications, offering a compelling combination of low on-resistance and fast switching performance. This device is a common choice for load switching, power management in portable devices, battery protection circuits, and DC-DC converters.

Datasheet Overview and Key Specifications

A thorough review of the FDS66733BZ datasheet reveals its critical electrical characteristics and absolute maximum ratings. Key parameters that define its performance include:

Drain-Source Voltage (V_DS): -30V. This defines the maximum voltage the MOSFET can block in the off-state.

Continuous Drain Current (I_D): -9.7A at T_C = 25°C. This is the maximum continuous current it can handle.

On-Resistance (R_DS(on)): A remarkably low < 16mΩ at V_GS = -10V. This is a crucial figure as it determines the conduction losses; a lower R_DS(on) means higher efficiency and less heat generation.

Gate Threshold Voltage (V_GS(th)): Typically -1.5V, making it suitable for low-voltage drive circuits, including those driven by 3.3V or 5V logic signals.

These specifications make it an excellent component for applications where minimizing power loss and saving board space are paramount.

Typical Application Circuit

A fundamental application for the FDS6673BZ is as a high-side load switch. In this configuration, the source is connected to the power rail (e.g., a battery's positive terminal), the drain is connected to the load, and the gate is controlled by a logic signal, often via a small N-Channel MOSFET or a dedicated load switch IC.

A standard circuit involves:

1. The FDS6673BZ placed between the power source and the load.

2. A gate resistor (e.g., 10kΩ) connected from the gate to the source. This ensures the MOSFET turns off reliably by pulling the gate to the source voltage when the drive signal is high-impedance.

3. An N-Channel MOSFET (e.g., a small-signal type like 2N7002) whose drain is connected to the gate of the FDS6673BZ, source to ground, and gate to the microcontroller (MCU) signal.

4. When the MCU output is HIGH, the N-Channel MOSFET turns on, pulling the gate of the P-Channel MOSFET to ground. Since the source is at V_BAT, this creates a V_GS of -V_BAT, turning the FDS6673BZ on and powering the load.

5. When the MCU output is LOW, the N-Channel MOSFET is off, and the pull-up resistor brings the gate to the source potential, ensuring V_GS = 0V and the load switch is firmly off.

This circuit provides reverse polarity protection and allows a low-voltage MCU to control a higher-voltage power rail with minimal losses.

Replacement and Cross-Reference Guide

When the FDS6673BZ is unavailable, selecting a suitable replacement requires careful comparison of key parameters. Potential alternatives include:

Infineon IRLML6401: A very common and pin-compatible alternative, though with a slightly higher R_DS(on) and lower current rating. Suitable for many less demanding applications.

Diodes Incorporated DMG2305UX: Another strong candidate with similar characteristics and a SOT-23 package.

Vishay Si2345DS: A robust alternative offering comparable performance.

onsemi FDS6675AZ: A direct sibling from the same family with a lower R_DS(on) for even higher efficiency.

When selecting a replacement, engineers must verify:

Package Type (SOT-23)

V_DS must be equal to or greater than the original.

R_DS(on) should be as low or lower to avoid increased heating.

V_GS(th) must be compatible with the existing drive circuitry.

ICGOODFIND: The onsemi FDS6673BZ remains a highly effective P-Channel MOSFET for power switching tasks, prized for its low threshold voltage and minimal on-resistance. Understanding its datasheet is key to implementing it correctly in application circuits like load switches. When sourcing becomes challenging, a methodical approach to cross-referencing ensures a smooth and reliable design transition without compromising performance.

Keywords: P-Channel MOSFET, Low On-Resistance, Load Switch, Power Management, Cross-Reference