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BSS138-7-F

50V N-ch MOSFET, 200mA, 3.5Ω Rds, low Vth 1.5V, SOT-23-3

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Pieza del fabricante：

BSS138-7-F

Paquete：

SOT-23-3 (TO-236-3, 2.9 x 1.3 x 1.0mm, surface mount)

Descripción

Productos

The BSS138-7-F is a 50V N-channel logic-level enhancement-mode MOSFET from Diodes Incorporated with 200mA drain current, 3.5Ω RDS(on), and low gate threshold (1.5V max) in a SOT-23-3 package.

Especificaciones

VDS (Drain-Source Voltage)	50V
ID (Continuous Drain Current)	200mA @ TA=25°C
RDS(on) Max	3.5Ω @ VGS=10V, ID=220mA
RDS(on) Max (4.5V)	6.0Ω @ VGS=4.5V
VGS(th) (Gate Threshold)	0.8V to 1.5V @ ID=1mA
VGS (Gate-Source Voltage)	±20V max
Qg (Total Gate Charge)	1.7nC typical @ VGS=10V
Ciss (Input Capacitance)	27pF typical @ VDS=25V
gfs (Forward Transconductance)	100mS typical
Power Dissipation	360mW @ TA=25°C
RθJA	350°C/W
Temperatura de funcionamiento	-55°C to +150°C
Paquete	SOT-23-3 (2.9 x 1.3mm, surface mount)

Características

50V N-channel enhancement-mode MOSFET
Low gate threshold voltage: 1.5V max
Directly drivable from 2.5V/3.3V MCU GPIO
Low on-resistance: 3.5Ω max at VGS=10V
Fast switching: 2.5ns turn-on delay typical
Pb-free and halogen-free
Industry-standard SOT-23-3 footprint

Aplicaciones

I2C/SPI level shifting (bidirectional)
Low-voltage logic switching
Load switch for battery-powered devices
Small servo motor control
MOSFET gate driver pre-driver

Introducción del producto:BSS138-7-F Presentación del producto

The BSS138-7-F from Diodes Incorporated is a 50V N-channel logic-level enhancement-mode MOSFET specifically designed for low-voltage switching applications. The key differentiator is the low gate threshold voltage (0.8V to 1.5V), which allows the device to be fully turned on by 3.3V or even 2.5V MCU GPIO pins without level translation. At VGS=4.5V, RDS(on) is 6Ω max, and at VGS=10V, it drops to 3.5Ω max. The 200mA continuous current rating covers typical I2C pull-up, LED indicator, and small relay loads. The SOT-23-3 package occupies minimal board area. The BSS138 is the industry-standard choice for bidirectional I2C level-shifter circuits, where two MOSFETs and pull-up resistors translate between 3.3V and 5V logic domains. The -7-F suffix denotes tape-and-reel packaging with Pb-free finish.

Principio de funcionamiento:BSS138-7-F Principio de funcionamiento

The BSS138-7-F operates as an enhancement-mode N-channel MOSFET. The low gate threshold voltage (0.8V typical, 1.5V max) means the channel begins to form at very low VGS. At VGS = 2.5V (low-voltage MCU output), the device is partially enhanced and can pass tens of milliamps with moderate RDS(on). At VGS = 3.3V, the device is more fully enhanced, and at VGS = 5V or 10V, it is fully enhanced with minimum RDS(on). The most common application is the bidirectional I2C level shifter: two BSS138 MOSFETs connect a 3.3V I2C bus to a 5V I2C bus. The gate is tied to the lower voltage (3.3V), and each side has pull-up resistors to its respective supply. When neither side pulls the line LOW, both FETs are off (VGS ≈ 0V since source = gate voltage). When the 3.3V side pulls LOW, the MOSFET’s body diode conducts, pulling the 5V side LOW through the channel. When the 5V side pulls LOW, the VGS exceeds the threshold (3.3V gate – ~0V drain), the MOSFET turns on, and the 3.3V side is pulled LOW. This bidirectional translation works without any direction control signal.

Descripción de la clavija:BSS138-7-F Definición y funciones de las clavijas

Pin	Nombre	Tipo	Descripción
1	Puerta	Entrada	Gate control terminal. Low-threshold N-channel MOSFET with VGS(th) = 0.8-1.5V, making it suitable for 2.5V-3.3V logic level shifting. The K suffix version includes ESD protection on the gate. Gate leakage current is typically 10nA. Maximum VGS = ±20V.
2	Fuente	Potencia de salida	Source terminal. In level-shifting applications, connects to the lower-voltage side (e.g., 3.3V logic). Internal body diode conducts from Source to Drain. Continuous drain current is 220mA at TC=25°C. On-resistance RDS(on) = 3.5Ω max at VGS=10V, ID=50mA.
3	Drenaje	Potencia de salida	Drain terminal. In level-shifting applications, connects to the higher-voltage side (e.g., 5V logic) through a pull-up resistor. Maximum VDS = 50V. Open-drain configuration allows bidirectional level shifting between two voltage domains with a single device and two pull-up resistors.

BSS138K-7 pin assignment (SOT-23-3, top view): Pin 1 (left) = Gate, Pin 2 (center, tab) = Source, Pin 3 (right) = Drain. The K suffix indicates ESD-protected gate variant. This is the industry-standard MOSFET for I2C/SPI bidirectional level shifting between 1.8V/2.5V/3.3V/5V logic domains. For higher current switching, SI2302CDS offers 2.2A with 62mΩ RDS(on) in the same SOT-23-3 package.

Application Scenarios:In which products and applications isBSS138-7-F usado

I2C Level Shift: Two BSS138 + 4 pull-ups create bidirectional 3.3V-to-5V I2C translator; low Vth ensures conduction at 3.3V
2.5V GPIO Switch: Low 1.5V threshold allows 2.5V MCU to drive gate; switches <50mA loads directly
Battery Load Switch: 0.5µA max gate leakage preserves battery; EN pin of MCU toggles VGS
Servo Control: 200mA rating drives small hobby servo signal lines; gate from MCU PWM pin
Gate Pre-Driver: Fast 2.5ns turn-on drives larger power MOSFET gates; reduces MCU drive requirement

Alternative Models:What chips are recommended as replacements for BSS138-7-F

Modelo	Fabricante	Diferencia clave	Paquete	Specs
BSS138LT1G	onsemi	Same function, onsemi version, SOT-23-3	-	-
2N7002K-7	Diodos Inc	60V/380mA, higher Vth (2.5V), ESD protected	-	-
BSS138PW	Nexperia	Same in TSSOP-6 (SOT-363) smaller package	-	-
2N7002ET1G	onsemi	60V/300mA, higher voltage, similar low-Vth	-	-
NTR4003NT1G	onsemi	30V/500mA, lower Rds, logic-level, SOT-23-3	-	-

BSS138-7-F is a 50V/220mA N-channel MOSFET from onsemi in SOT-23-3 with 3.5Ω RDS(on). The BSS138K-7 provides ESD-protected gate. The 2N7002K-7 from onsemi offers 60V/300mA with 1.2Ω and ESD protection. The SI2302CDS from Vishay provides 20V/2.2A with 62mΩ for higher current. The DMN2075U from Diodes Inc offers 20V/750mA with 90mΩ. For level-shifting, BSS138 remains the industry standard for I2C bidirectional shifting. The AO3400A from Alpha & Omega provides 30V/5A with 26mΩ in the same SOT-23.