BSS138-7-F

The Diodes Incorporated BSS138-7-F is an N-Channel enhancement mode MOSFET designed for low-power switching and level-shifting applications. With a low gate threshold voltage of 0.5V to 1.5V, the device can be driven directly from 1.8V, 2.5V, or 3.3V logic signals, making it ideal for bidirectional voltage level translation on I2C and SPI buses. The 50V drain-source rating provides ample margin for typical interface voltage translation scenarios. The SOT-23-3 surface-mount package occupies minimal board space while providing 300mW power dissipation capability. The device is AEC-Q101 qualified, making it suitable for automotive applications. It is lead-free, halogen-free, and fully RoHS compliant as a Green device.

The BSS138-7-F operates as a voltage-controlled N-Channel enhancement-mode MOSFET: 1) Gate Control: When VGS exceeds the threshold voltage (0.5-1.5V), an inversion layer forms in the P-body, creating a conductive channel between drain and source. The low threshold voltage enables logic-level gate drive from low-voltage microcontrollers. 2) Conduction: At VGS=10V, RDS(on) is 1.4Ohm typical (3.5Ohm max), providing efficient current conduction for low-power switching applications. At lower VGS values, RDS(on) increases but remains sufficient for level-shifting applications where current is minimal. 3) Level Shifting: When used in a common-gate configuration with a pull-up resistor on the drain, the BSS138 can translate logic signals between different voltage domains. When one side drives low, the MOSFET conducts and pulls the other side low; when released, both sides are pulled high by their respective pull-up resistors. 4) Switching: The low 50pF input capacitance and 20ns switching delays enable fast signal transitions for I2C speeds up to 400kHz and beyond.

• Bidirectional I2C and SPI voltage level shifting between 1.8V/2.5V/3.3V/5V domains
• System and load switching in battery-powered portable devices
• Logic-level signal driving and interfacing
• Low-power relay and LED driving
• General-purpose switching in consumer and automotive electronics