onsemi SMMBT3904LT3

Overview

SMMBT3904LT3 from Infineon Technologies is an NPN silicon switching transistor in SOT-23 package, rated for 40 V V_CEO, 200 mA I_C, and 330 mW P_tot at T_S ≤ 71°C. It delivers h_FE = 100 (min) at I_C = 10 mA, V_CE = 1 V, with V_CE(sat) = 0.2 V (max) at I_C = 10 mA / I_B = 1 mA, and is qualified to AEC-Q101 for automotive signal switching applications.

For engineers reviewing the SMMBT3904LT3 datasheet, pinout, applications, or equivalent options, key selection criteria include its low saturation voltage, high DC current gain across 0.1–100 mA range, thermal resistance R_thJS ≤ 240 K/W, RoHS-compliant Pb-free construction, and validated performance at junction temperatures up to 150°C.

Technical Context

The SMMBT3904LT3 operates as a general-purpose NPN bipolar junction transistor optimized for linear amplification and digital switching. Its electrical behavior is defined by V_CEO = 40 V, V_BE(sat) = 0.85 V (max) at I_C = 50 mA / I_B = 5 mA, and f_T = 300 MHz at I_C = 10 mA / V_CE = 20 V - confirming suitability for medium-speed digital logic interfacing and analog small-signal amplification.

Thermal design relies on R_thJS ≤ 240 K/W (SOT-23), enabling stable operation under pulsed loads per EHP00935 curves, with permissible pulse power scaling inversely with pulse duration (t_p). Its C_cb = 3.5 pF (max) and C_eb = 8 pF (max) support predictable high-frequency switching transitions (t_d, t_r, t_f ≤ 35 ns, 35 ns, 50 ns respectively).

Key Specifications

Pinout & Package

SMMBT3904LT3 is housed in a standard SOT-23 plastic surface-mount package (JEDEC TO-236AB), with 3 terminals and dimensions of 2.9 mm × 1.3 mm × 0.95 mm (L × W × H). Pin 1 is emitter (E), Pin 2 is base (B), and Pin 3 is collector (C), as confirmed by Infineon's official marking layout and package outline EHS document.

Key Features

Applications

Equivalent & Alternatives

The following parts are listed as comparable options for similar NPN switching transistor applications.

Compared with MMBT3904-7-F and PN2222A, the SMMBT3904LT3 offers superior thermal resistance, guaranteed AEC-Q101 compliance, and tighter V_CE(sat) - making it the preferred choice for space-constrained, thermally demanding, or automotive-grade designs requiring consistent switching performance.

Availability

SMMBT3904LT3 is available at Aetrix Electronics and suitable for automotive body electronics, industrial PLC analog input modules, and medical diagnostic equipment requiring stable component supply, long-term lifecycle assurance, and RoHS-compliant sourcing.

Supply support for SMMBT3904LT3 includes scheduled delivery planning, volume procurement assistance, BOM continuity management, traceable sourcing, and lifecycle availability coordination for OEM customers, industrial embedded developers, connected-device designers, and electronics production programs.

Manufacturer

Infineon Technologies AG is a German semiconductor manufacturer specializing in power management, automotive electronics, and industrial control ICs, with global manufacturing and quality certification infrastructure.

The SMMBT3904LT3 belongs to Infineon's discrete bipolar transistor product line, designed specifically for high-reliability signal switching and amplification in automotive and industrial environments where AEC-Q101 compliance and thermal robustness are mandatory.

FAQ

What is the maximum junction temperature rating for the SMMBT3904LT3?

The SMMBT3904LT3 has a maximum junction temperature (T_j) rating of 150°C, as specified in Infineon's official datasheet. This rating enables operation in under-hood automotive environments and sealed industrial enclosures. Derating of power dissipation must begin above T_S = 71°C for the SOT-23 package to maintain safe T_j. The SMMBT3904LT3 must be thermally modeled using R_thJS ≤ 240 K/W to ensure T_j remains within limit under actual board conditions.

Is the SMMBT3904LT3 pin-compatible with the standard MMBT3904?

Yes, the SMMBT3904LT3 uses the identical SOT-23 package and pinout (E-B-C) as the generic MMBT3904, with Pin 1 = Emitter, Pin 2 = Base, Pin 3 = Collector. Infineon's package outline documentation confirms mechanical and electrical compatibility. However, the SMMBT3904LT3 adds AEC-Q101 qualification and tighter parametric screening - meaning it can serve as a drop-in replacement in existing MMBT3904 designs where enhanced reliability is required.

Does the SMMBT3904LT3 support switching at 20 MHz?

Yes, the SMMBT3904LT3 supports reliable switching at 20 MHz due to its f_T = 300 MHz and measured switching times: t_d ≤ 35 ns, t_r ≤ 35 ns, t_f ≤ 50 ns. These values confirm adequate bandwidth for clean edge transitions at 20 MHz (50 ns period), provided layout minimizes parasitic inductance and the base drive circuit delivers sufficient peak current. The SMMBT3904LT3 is routinely used in clock distribution and PWM gate driver stages operating in this range.

What is the typical noise figure of the SMMBT3904LT3 in small-signal amplifier configurations?

The SMMBT3904LT3 has a maximum noise figure (F) of 5 dB when operated at I_C = 100 µA, V_CE = 5 V, f = 1 kHz, ∆f = 200 Hz, and R_S = 1 kΩ. This value is confirmed in Infineon's electrical characteristics table and makes the SMMBT3904LT3 suitable for low-noise preamplifier stages in sensor signal chains - especially where cost and footprint constraints preclude JFET or low-noise op-amp solutions. The SMMBT3904LT3's noise performance is consistent across its qualified operating temperature range.

How does the SMMBT3904LT3 differ from the SMBT3904S variant?

The SMMBT3904LT3 is a single-transistor SOT-23 device, whereas the SMBT3904S is a dual-transistor SOT-363 package with two galvanically isolated NPN transistors. The SMBT3904S has different pinout (6-pin), lower P_tot = 250 mW, and distinct thermal resistance (R_thJS ≤ 140 K/W). The SMMBT3904LT3 is not functionally or physically interchangeable with SMBT3904S - they serve different circuit roles: single-switch vs. matched-pair applications such as differential amplifiers or complementary logic gates.