BSS138LT1G - 50V 200mA N-Channel MOSFET SOT-23 | onsemi
MPN: BSS138LT1G β Active| Qty | Unit Price | Extended |
|---|---|---|
| 1 | $0.28 | $0.28 |
| 10 | $0.22 | $2.20 |
| 100 | $0.14 | $14.00 |
| 500 | $0.1 | $50.00 |
| 1,000 | $0.08 | $80.00 |
Drop-in alternatives for BSS138LT1G β same package, pin-to-pin compatible. Different-package parts requiring PCB rework are excluded.
Quick Comparison Tool β Select alternative parts for side-by-side comparison:
BSS138LT1
β Drop-Inπ Reference alternative (not in catalog)
2N7002LT1G
β Drop-Inβ In Stock
$0.02 / Unit
View Datasheet βBSS138W-7-F
β Drop-Inπ Reference alternative (not in catalog)
BSS138-13
β Drop-Inπ Reference alternative (not in catalog)
BSS138LT1G Maximum Ratings & Electrical Characteristics
| Transistor Type | N-Channel MOSFET |
| Drain-Source Voltage (VDS) | 50 V |
| Continuous Drain Current (ID) | 200 mA (Ta) |
| Power Dissipation (PD) | 225 mW (Ta) |
| On-Resistance Max (RDS(on)) | 3.5 ohm |
| Configuration | Single FET |
| Channel Mode | Enhancement Mode |
| Package | SOT-23-3 (TO-236) |
| Mounting Type | Surface Mount |
| RoHS Status | Compliant (RoHS Compliant and Pb-free per Easybom) |
| Product Family | BSS138LT Series Small Signal MOSFET |
| Typical Applications | Computers, printers, cordless phones, DC-DC converters |
BSS138LT1G Pin Configuration
| Pin 1 | G β Gate - controls channel conduction |
| Pin 2 | D β Drain - current terminal, connect to load |
| Pin 3 | S β Source - current terminal, connect to ground (low-side switching) |
Safe Operating Area
Typical Applications
BSS138LT1G is suitable for 6 applications: I2C Logic Level Shifting, Low-Side Load Switching in Battery-Powered Products, Relay and Solenoid Drivers, DC-DC Converter Peripheral Switching, LED Indicators and Backlight Drivers, Open-Drain Logic Interfaces and Signal Gating.
I2C Logic Level Shifting
The BSS138LT1G is the canonical transistor for the two-MOSFET bidirectional I2C level shifting topology used to connect 3.3 V microcontrollers to 5 V sensors and peripherals. Its low gate threshold voltage (around 0.5 V typical per Components101) guarantees that a valid low level propagates across domains, while its small gate capacitance preserves I2C rise times at 100 kHz and 400 kHz. The gate ties to the lower rail, source to the low-voltage bus, and drain to the 5 V bus with pull-up resistors. The SOT-23 footprint lets both channels fit in a few square millimeters, and the 50 V rating is far above bus voltages, giving robust margin against transients.
Recommended
Low-Side Load Switching in Battery-Powered Products
In portable and battery-powered products such as cordless phones, printers and computers, the BSS138LT1G serves as a low-side switch that lets an MCU GPIO disconnect power from sub-circuits. The logic-level gate threshold allows direct drive from 3 V and 5 V logic without a gate driver, and the 3.5 ohm maximum RDS(on) keeps conduction losses modest at the rated 200 mA. The 50 V drain rating provides generous margin over single-cell and multi-cell battery configurations. Its SOT-23 package occupies minimal board area in dense portable layouts. Designers should keep continuous load currents below 200 mA and verify that I2R dissipation stays under the 225 mW limit at maximum ambient temperature.
Recommended
Relay and Solenoid Drivers
The BSS138LT1G is well suited to driving small signal relays, solenoids and indicators in cordless phones, printers and consumer appliances. Its enhancement-mode N-channel structure switches the low side of the coil directly from logic, while the intrinsic body diode freewheels inductive current when the device turns off. With gate charge minimal, PWM dimming or fast switching adds negligible switching loss. At the rated 200 mA continuous current the estimated conduction dissipation of 140 mW (I2R at 3.5 ohm) sits within the 225 mW package limit. The 50 V rating absorbs the inductive kick that escapes the freewheeling path, adding ruggedness in cost-sensitive designs.
Recommended
DC-DC Converter Peripheral Switching
The BSS138LT series is explicitly positioned by onsemi and distributors for DC-DC converter applications, where it performs auxiliary switching tasks such as enable FETs, power-good gating, and small load disconnects around the main converter. The 50 V VDS rating comfortably covers 12 V, 24 V and 48 V intermediate bus architectures at low current, and the low threshold allows control from the converter controller's logic outputs. Its small SOT-23 body fits beside the power stage without layout penalty. Engineers should place the device close to the switched node, keep gate traces short to limit ringing, and confirm that steady-state drain current stays within the 200 mA Ta rating.
Recommended
LED Indicators and Backlight Drivers
The BSS138LT1G drives LED strings, status indicators and small display backlights from microcontroller GPIOs in consumer and industrial equipment. Operating as a low-side switch, it sinks LED current with a logic-level gate, and the 3.5 ohm on-resistance contributes negligible voltage drop even at the full 200 mA rating. PWM dimming is clean because of the device's small gate charge and fast switching. The 225 mW dissipation ceiling is comfortably above typical indicator LED loads. The compact SOT-23 (TO-236) footprint suits dense indicator clusters on front-panel PCBs, and the 50 V rating gives wide margin on 12 V and 24 V indicator rails.
Recommended
Open-Drain Logic Interfaces and Signal Gating
In computer, printer and telecom boards, the BSS138LT1G functions as an open-drain buffer: pulling interrupt lines, status flags or reset signals low, or gating one signal domain into another. Because the drain is floating when off, multiple devices can share a single pulled-up line exactly like an open-collector output, enabling wired-AND logic. The low gate threshold permits control directly from 3.3 V and 5 V logic families, and the 50 V rating covers legacy 24 V and 48 V signaling found in industrial boards. Designers should size the pull-up resistor so sink current stays well inside the 200 mA rating and confirm noise margins at the receiving logic.
Recommended
Recommended Products Summary
Engineering reference data for BSS138LT1G β comparison, design guidance, and compliance information.
Selection Guide
Comparison with Alternatives
| Parameter | This Product | BSS138LT1 | 2N7002LT1G | BSS138W-7-F | BSS138-13 |
|---|---|---|---|---|---|
| Package | SOT-23-3 (TO-236) | SOT-23-3 (TO-236) - same | SOT-23-3 (TO-236) - same | SOT-23-3 (TO-236) - same | SOT-23-3 (TO-236) - same |
| Brand | onsemi | onsemi | onsemi | Diodes Incorporated | Diodes Incorporated |
| Drain-Source Voltage | 50 V | 50 V | 60 V | 50 V | 50 V |
| Continuous Drain Current | 200 mA (Ta) | 200 mA (Ta) | [DATA_NEEDED] | [DATA_NEEDED] | [DATA_NEEDED] |
| Max On-Resistance | 3.5 ohm | 3.5 ohm | Higher than BSS138 (per Easybom) | 3.5 ohm class (per Xecor identical profile) | [DATA_NEEDED] |
| RoHS / Lead-Free | Compliant (Pb-free) | Non-compliant (obsolete, Pb-containing) | Compliant (G suffix) | Compliant (-F suffix) | [DATA_NEEDED] |
| Lifecycle Status | Active | Obsolete (replaced by BSS138LT1G) | Active | Active | Active |
| Pin Configuration | 1=Gate, 2=Drain, 3=Source | 1=G, 2=D, 3=S - identical | Verify datasheet - family uses different G/D/S convention in some variants | 1=G, 2=D, 3=S - BSS138 standard | 1=G, 2=D, 3=S - BSS138 standard |
Key Differentiators
- Low gate threshold for direct 3.3 V logic drive (vs 2N7002LT1G)
- Proven cross-brand second sourcing (vs BSS138W-7-F)
- RoHS-compliant active lifecycle (vs BSS138LT1)
Design Notes
The SOT-23-3 package is rated for 225 mW at 25 C ambient with no heatsink possible; cooling happens through the PCB copper. Estimated: at the full 200 mA rating and 3.5 ohm maximum RDS(on), conduction dissipation is I2R = 140 mW, leaving limited margin in high-ambient environments. For continuous loads above roughly 150 mA, pour copper on the drain and source pads on both layers and verify junction temperature against your derating policy. Consider pulsing rather than holding high currents.
Place the BSS138LT1G with short, wide traces on gate and source to minimize parasitic inductance and gate ringing, especially in PWM circuits. Keep the gate trace away from the drain node to reduce Miller-coupled switching artifacts. When using the device as an I2C level shifter, keep source and drain traces short to the pull-up resistor network to preserve bus rise time at 400 kHz. The SOT-23 land pattern is standard; no special footprint work is needed for the drop-in alternatives listed on this page.
Never rely on the 2N7002LT1G as a blind substitute in level shifter or low-drop load switch circuits: although it shares the SOT-23 footprint, Easybom notes it carries a rather high on-resistance and a higher gate threshold, which can raise bus low levels or prevent switching from 3.3 V GPIO. Also verify pin order on any substitute, since not all SOT-23 small-signal MOSFETs share the BSS138 G-D-S convention. Stay within the 50 V VDS rating including inductive spikes.
Add a series gate resistor (estimated 100 ohm to 1 kilohm is typical) when driving from fast logic to control switching speed and damp ringing; when using the device as an open-drain buffer or level shifter, tie the gate directly to the lower supply rail instead. For inductive loads, always provide a freewheeling path - the intrinsic body diode handles small relays, but an external Schottky across the coil reduces stress. The 225 mW Ta rating assumes still air at 25 C; derate for enclosed products.
Compliance Information
RoHS Compliant and Pb-free per distributor data (Easybom) and onsemi G-suffix package code. REACH, halogen-free and conflict minerals status not stated in retrieved data - verify via onsemi product page compliance documents.
