BSS138LT1G

The BSS138LT1G is an N-channel small-signal MOSFET from onsemi with an exceptionally low gate threshold voltage (0.85V to 1.5V), making it ideal for direct drive from 1.8V and 2.5V logic levels. The 50V drain-source rating enables it to translate signals between different voltage domains, particularly popular for I2C and SPI bus level shifting between 1.8V/2.5V/3.3V rails. The SOT-23-3 package provides a compact footprint for space-constrained designs. An AEC-Q101 qualified version (BVSS138L) is available for automotive applications.

The BSS138L operates as a voltage-controlled N-channel MOSFET with an enhancement mode gate structure. The low threshold voltage (VGS(th) 0.85-1.5V) means the channel begins conducting at very low gate voltages, enabling direct interface with low-voltage digital logic. In level-shifting applications, the MOSFET is connected with drain pulled up to the higher voltage rail via a resistor, and source tied to the lower voltage rail. When the low-voltage input drives the gate, the MOSFET conducts, pulling the drain toward the source voltage, effectively translating the logic level. The open-drain configuration makes it ideal for bidirectional I2C level shifting.

• I2C/SMBus bidirectional level shifting (1.8V to 3.3V)
• SPI UART logic level translation
• Low-voltage digital signal switching
• DC-DC converter low-power switching element
• Battery-powered portable device power gating