onsemi FDN5618P P-Channel MOSFET: Datasheet, Application Circuit, and Replacement Guide
The FDN5618P from onsemi is a popular P-Channel enhancement mode MOSFET designed for a wide range of low-voltage, high-speed switching applications. This surface-mount device, housed in a compact Space-Saving SC-70-3 / SOT-323 Package, is a go-to component for power management in portable electronics, battery-powered devices, and load switching circuits due to its efficient performance and small footprint.
Datasheet Overview and Key Specifications
A thorough review of the FDN5618P datasheet reveals its core electrical characteristics, which are critical for circuit design and component selection.
Drain-Source Voltage (VDS): -60V. This defines the maximum voltage the MOSFET can block in the off state.
Continuous Drain Current (ID): -1.7A. The maximum continuous current it can handle when fully turned on.
On-Resistance (RDS(on)): A remarkably low 95 mΩ (max) at VGS = -10V. This is a crucial figure as it determines the power loss and heating during conduction. A lower RDS(on) means higher efficiency.
Gate Threshold Voltage (VGS(th)): Typically between -0.8V and -2.5V. This indicates the minimum gate-to-source voltage required to start turning the device on.
Package: SC-70-3 (SOT-323), which is extremely beneficial for space-constrained PCB designs.
Typical Application Circuit: Load Switch
One of the most common uses for the FDN5618P is as a high-side load switch. This circuit allows a low-power logic signal (e.g., from a microcontroller) to control a high-power circuit (e.g., a motor or LED strip).
How it works:
1. The microcontroller GPIO pin is connected to the gate of the FDN5618P through a resistor (e.g., 10kΩ).
2. To turn the load OFF, the GPIO is set to a high-impedance state or logic high (e.g., 3.3V). Since the source is connected to the power rail (VDD), VGS ≈ 0V, keeping the MOSFET off.
3. To turn the load ON, the GPIO outputs logic low (0V). This creates a negative VGS relative to the source (VGS ≈ -3.3V), which is sufficient to fully enhance the MOSFET, allowing current to flow from the source to the drain and power the load.
A pull-up resistor on the gate is often used to ensure the MOSFET remains off if the microcontroller pin is undefined during startup. A series gate resistor can also be added to dampen any ringing.
Replacement and Cross-Reference Guide
When the FDN5618P is unavailable, selecting a suitable replacement requires careful comparison of key parameters. The replacement must be a P-Channel MOSFET in a compatible SOT-323 package.
Direct Equivalents/Alternatives:
Fairchild/ON Semiconductor FDN5618P: The original part.
Diodes Inc. ZXMP6A17FTA: A highly comparable alternative with similar VDS (-60V), RDS(on), and current rating.
Infineon IRLML6401TRPBF: While also a P-Channel MOSFET with similar specs, note its slightly different package (SOT-23) which may require a PCB layout change.
Key Parameters for Cross-Reference:
When selecting a replacement, ensure the new part meets or exceeds the following critical specifications of the FDN5618P:
1. VDS: Must be at least -60V.
2. ID: Must be at least -1.7A.
3. RDS(on): Should be similarly low (e.g., < 100 mΩ) at a VGS your circuit can provide (e.g., -4.5V or -10V).
4. VGS(th): Must be compatible with your drive voltage to ensure full enhancement.
5. Package: Must be SC-70-3 / SOT-323 for a drop-in replacement.
The onsemi FDN5618P stands out as an exceptionally efficient and compact solution for low-power switching tasks. Its low on-resistance and high-speed switching capability make it ideal for modern portable electronics where board space and power efficiency are paramount. By understanding its datasheet, implementing it correctly in application circuits like a high-side switch, and knowing how to find a proper replacement, designers can effectively leverage this component to create robust and efficient designs.
Keywords:
P-Channel MOSFET
Load Switch
SC-70-3 Package
Low On-Resistance
High-Side Switching
