NXP Semiconductors BAP51-04W,115

Overview

BAP51-04W from NXP Semiconductors (formerly Philips) is a general-purpose dual-element PIN diode in series configuration housed in an SOT323 plastic SMD package. It delivers 0.4 pF capacitance at 0 V reverse bias, 1.5–2.5 Ω forward resistance at 10 mA/100 MHz, and supports RF switching up to 2.5 GHz with < −40 dB isolation at zero bias - used in antenna tuning and transmit/receive (T/R) switch modules.

For engineers reviewing the BAP51-04W datasheet, BAP51-04W pinout, BAP51-04W application, or BAP51-04W equivalent, key selection criteria include its low-series-inductance (1.6 nH), fast charge-carrier lifetime (550 ns), dual-diode topology for enhanced voltage handling, and compatibility with 50 Ω RF stripline circuits requiring minimal insertion loss.

Technical Context

The BAP51-04W integrates two planar PIN diodes in series within a single SOT323 package, enabling higher reverse voltage tolerance (50 V per diode) without increasing footprint. Its low capacitance (0.2–0.55 pF across 1–5 V reverse bias) and tunable forward resistance (1.5–9 Ω across 0.5–10 mA) support broadband RF control from HF through S-band.

Thermal resistance from junction to soldering point is 250 K/W, supporting stable operation under pulsed RF conditions. The device operates over −65 °C to +150 °C and is rated for 240 mW total power dissipation at 90 °C soldering-point temperature.

Key Specifications

Pinout & Package

Package: SOT323 (SC-70), 3-lead plastic surface-mount package, 2.2 mm × 1.35 mm × 0.95 mm body size, lead pitch 0.65 mm.

Key Features

Applications

Equivalent & Alternatives

The following parts are listed as comparable options for similar PIN diode switching applications.

Compared with SMP1320-079LF and BAP64-04W, the BAP51-04W uniquely delivers 50 V standoff in a standard SOT323 footprint via integrated series diodes - eliminating external stacking while maintaining low capacitance and sub-3 Ω on-resistance at 10 mA.

Availability

BAP51-04W is available at Aetrix Electronics and suitable for RF front-end design, antenna tuning modules, and T/R switch development requiring stable component supply, consistent parametric performance, and long-term industrial availability.

Supply support for BAP51-04W 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

NXP Semiconductors is a global semiconductor leader focused on secure connectivity solutions for automotive, industrial, and IoT applications, with legacy roots in Philips' discrete device innovation.

The BAP51-04W belongs to NXP's general-purpose RF PIN diode product line, engineered specifically for compact, high-linearity RF switching and attenuation in space-constrained wireless infrastructure and mobile front ends.

FAQ

What is the maximum reverse voltage rating for the BAP51-04W?

The BAP51-04W has a continuous reverse voltage rating of 50 V per diode. Because it contains two PIN diodes in series, the total standoff capability remains 50 V - not 100 V - as the internal common node is not accessible for independent biasing. This rating is specified under limiting values per IEC 60134 and must not be exceeded to avoid junction breakdown. The BAP51-04W datasheet confirms VR = 50 V at Tj = 25 °C with no derating required up to 90 °C soldering-point temperature.

How does the BAP51-04W achieve low capacitance while maintaining robust RF power handling?

The BAP51-04W achieves 0.2–0.55 pF capacitance via optimized planar PIN junction geometry and intrinsic layer doping profile, which minimizes depletion-region overlap without sacrificing carrier lifetime. Its 240 mW power dissipation rating at Ts = 90 °C and 250 K/W thermal resistance enable reliable RF power handling up to 30 dBm in pulsed operation. The BAP51-04W's low series inductance (1.6 nH) further prevents self-resonance, preserving low capacitance behavior through S-band.

Can the BAP51-04W be used in a shunt configuration?

No - the BAP51-04W is configured exclusively as two series-connected diodes with only three external terminals (anode, cathode, and internal common node), making true shunt implementation impossible without external re-routing. Pin 3 is not externally accessible; it is the internal cathode/anode junction. For shunt switching, discrete single-diode alternatives like BAP64-04W or SMP1320-079LF must be used. The BAP51-04W is designed strictly for series-switched RF paths, as confirmed by its symbol, pinning diagram, and application curves in the official datasheet.

What is the typical forward voltage of the BAP51-04W at 50 mA?

The BAP51-04W exhibits a typical forward voltage of 0.95 V at IF = 50 mA and Tj = 25 °C, with a maximum of 1.1 V under the same conditions. This value reflects the combined VF of both series diodes, consistent with silicon PIN behavior. At lower currents (e.g., 10 mA), VF drops to ~0.85 V. These values are measured per diode - meaning the total applied voltage across pins 1 and 2 equals twice the per-diode VF - and are critical for designing bias networks that avoid excessive DC power dissipation in RF switch drivers.

Does the BAP51-04W require external DC blocking capacitors in RF signal paths?

Yes - because the BAP51-04W requires forward DC bias to actuate its low-resistance state, external DC blocking capacitors (typically 100 pF ceramic) must be placed in series with RF ports (pins 1 and 2) to prevent bias leakage into adjacent circuitry. The internal common node (pin 3) is inaccessible, so bias must be injected via RF chokes on both sides. This configuration is validated in the BAP51-04W's application schematics for T/R switching and is essential to maintain 50 Ω impedance continuity while isolating DC bias from sensitive RF components like LNAs or power amplifiers.