BB145B,115 - Low-Voltage Varactor 2.75pF SOD-523 | NXP
MPN: BB145B,115 β Active| Qty | Unit Price | Extended |
|---|---|---|
| 1 | $0.15 | $0.15 |
| 10 | $0.14 | $1.40 |
| 100 | $0.13 | $13.00 |
| 500 | $0.125 | $62.50 |
| 1,000 | $0.12 | $120.00 |
BB145B,115 Overview
A varactor diode, also called a varicap or tuning diode, is a semiconductor device operated in reverse bias so that its junction capacitance varies with the applied voltage. Within the voltage regulator and tuning diode hierarchy, varactors serve as voltage-controlled capacitors in resonant LC tanks, enabling electronic tuning without mechanical components. They are fundamental building blocks of voltage-controlled oscillators (VCOs), RF filters, and phase-locked loop (PLL) tuning circuits.
Key features of the BB145B include a maximum capacitance (Cd) of 7.2 pF at low reverse voltage, a low series resistance that preserves Q factor in resonant tanks, and operation at reverse voltages up to 8 V (VRRM), making it well matched to 3.3 V and 5 V low-voltage tuning systems. The planar technology construction provides stable, repeatable capacitance-versus-voltage characteristics across production lots.
The device sustains an average forward current of 20 mA and operates over an industrial temperature range of -55C to +150C, allowing use in outdoor wireless modules and automotive-adjacent environments. Its tiny SOD-523 footprint (approximately 1.2 x 0.8 mm body) supports dense RF layouts on modern PCBs.
Typical applications include voltage-controlled oscillators for RF transceivers, LC tank tuning in wireless receivers, electronically tuned filters, and capacitance trimming in matching networks. According to the NXP product page, the part ships on 7-inch reels with a minimum package quantity of 3000.
Design consideration: because tuning range is set by the VRRM limit of 8 V, ensure the tuning voltage never exceeds this rating; place the varactor in the tank with proper DC blocking and high-value series resistors to isolate RF from the tuning source.
This page synthesizes distributor pricing, drop-in alternatives, and practical RF design notes not found in the manufacturer datasheet.
Drop-in alternatives for BB145B,115 β same package, pin-to-pin compatible. Different-package parts requiring PCB rework are excluded.
Variants in this series
Same-series models that are drop-in compatible with BB145B,115 (same form factor and footprint) β differing in Configuration, Device Type, Operating Temperature Range, Packaging.
Quick Comparison Tool β Select alternative parts for side-by-side comparison:
BB145,115
β Drop-Inπ Reference alternative (not in catalog)
BB145B,115 Maximum Ratings & Electrical Characteristics
| Device Type | Varactor (variable capacitance) diode |
| Nominal Capacitance (Cd) | 2.75 pF at C4 condition |
| Capacitance Ratio | 2.4 |
| Maximum Capacitance Cd | 7.2 pF (at low reverse voltage) |
| Repetitive Reverse Voltage (VRRM) | 8 V |
| Working Reverse Voltage | 6 V |
| Average Forward Current (IF(AV)) | 20 mA |
| Operating Temperature Range | -55C to +150C |
| Technology | Planar |
| Package | SOD-523 (SC-79) |
| Mounting Type | Surface Mount |
| Configuration | Single diode |
| Primary Application | Voltage controlled oscillators (VCO) |
| Packaging | Reel 7-inch (Q1/T1) |
| Minimum Package Quantity | 3000 |
BB145B,115 Pin Configuration
| Pin 1 | Cathode β Cathode terminal; polarity band on package body; connect toward positive tuning (reverse-bias) voltage |
| Pin 2 | Anode β Anode terminal; connect toward tank/ground side of tuning circuit |
Typical Applications
BB145B,115 is suitable for 6 applications: Voltage Controlled Oscillators (VCO), Electronically Tuned RF Filters, PLL Frequency Synthesizer Tuning, Capacitance Trimming in Matching Networks, Portable and Battery-Powered Radios, Test and Measurement Instrument Tuning.
Voltage Controlled Oscillators (VCO)
The BB145B,115 is explicitly designed for VCO duty: NXP describes it as a low-voltage variable capacitance diode for voltage controlled oscillators. Its 2.75 pF nominal capacitance with a 2.4 capacitance ratio gives a usable tuning span in an LC tank, while the 8 V VRRM rating comfortably covers 3.3 V PLL tuning rails. In a typical Colpitts or Clapp VCO, the diode is DC-isolated from the tank through coupling capacitors and driven by a tuning voltage through a high-value series resistor, keeping RF out of the control line. Its low series resistance helps maintain tank Q, directly supporting low phase noise performance in receivers and frequency synthesizers.
Recommended
Electronically Tuned RF Filters
In tunable bandpass and lowpass LC filters, the BB145B,115 replaces switched capacitor banks with a continuously variable element. Because the capacitance ratio is 2.4, a single diode can shift a filter's corner frequency by roughly a factor of sqrt(2.4) approximately 1.55x across the tuning sweep, which is enough for band-select preselection in multiband receivers. The -55C to +150C operating range keeps the filter response stable in outdoor enclosures. Designers should bias each diode through separate high-value resistors to avoid intermodulation between filter nodes, and choose 1% or better inductors so the tuning law remains predictable over production units.
Recommended
PLL Frequency Synthesizer Tuning
In PLL-based synthesizers, the BB145B,115 acts as the tuning element whose reverse bias is set by the phase-detector output of the loop. The 2.75 pF / 2.4 ratio characteristics let a 3.3 V charge pump cover the oscillator's required frequency range without high-voltage level shifting. Low series resistance minimizes loading of the tank and preserves loop gain. A typical loop filter (second-order RC) between charge pump and varactor suppresses reference spurs; the diode's stable planar construction ensures the loop's tuning constant stays constant over -55C to +150C, reducing recalibration needs in fielded radio equipment.
Recommended
Capacitance Trimming in Matching Networks
RF matching networks often need post-production trimming to compensate for PCB parasitics and antenna tolerance. The BB145B,115 provides voltage-controlled fine trimming at 2.75 pF nominal - a value directly in the range of input-matching capacitors for 433 MHz, 868 MHz, and 915 MHz ISM-band antennas. Applying 0 to 6 V of reverse bias sweeps the effective capacitance across its 2.4 ratio, letting a microcontroller DAC optimize VSWR without mechanical adjustment. Because the SOD-523 body is about 1.2 x 0.8 mm, the trim element adds negligible parasitic series inductance compared with larger varactor packages.
Recommended
Portable and Battery-Powered Radios
The BB145B,115 targets low-voltage designs, so it integrates naturally into 3 V battery-powered radios and wireless sensor nodes. The 6 V working reverse voltage and 8 V absolute limit mean no charge-pump overhead is needed above the battery rail, and the diode draws effectively zero DC current in reverse bias, preserving battery life during receive tuning. The -55C to +150C range tolerates glove-compartment and outdoor conditions. Designers should note the NXP 99-week factory lead time and plan to buy from distributor stock (DigiKey ships same day as of 2026-09-13) for portable-product service spares.
Recommended
Test and Measurement Instrument Tuning
Bench instruments such as signal generators, grid-dip meters, and analyzer front ends benefit from the BB145B,115's predictable, repeatable C-V curve produced by NXP's planar process. Its 2.75 pF nominal value suits harmonic tanks in the tens-to-hundreds of megahertz, and 20 mA forward-current capability adds robustness against accidental forward conduction during fault conditions. In sweep generators, a sawtooth tuning voltage applied across the diode yields a proportional frequency sweep; the flat series resistance keeps sweep linearity acceptable without linearization correction in most mid-band designs, simplifying the analog control chain.
Recommended
Recommended Products Summary
Engineering reference data for BB145B,115 β comparison, design guidance, and compliance information.
Selection Guide
Comparison with Alternatives
| Parameter | This Product | BB145,115 |
|---|---|---|
| Package | SOD-523 (SC-79) | SOD-523 (SC-79) - same |
| Brand | NXP Semiconductors | NXP Semiconductors |
Key Differentiators
- True low-voltage tuning diode (vs BB145,115)
- Ultra-small footprint (vs BB145,115)
- Low-voltage system fit (vs BB145,115)
Design Notes
Feed the tuning voltage through a high-value series resistor (typically 10k-100k ohm) and decouple it with a 10 nF-100 nF capacitor to ground. This prevents the low-impedance tuning source from shunting RF tank energy and stops oscillator noise from coupling back into the PLL. Keep the varactor's RF path short: SOD-523's tiny body adds little series inductance, but long traces will degrade tank Q and shift the tuning law.
Never exceed the 8 V repetitive reverse voltage rating on the BB145B,115 tuning line - transient overshoot from charge pumps or hot-plug events can degrade the junction and permanently shift the 2.75 pF nominal capacitance. Add a clamp or zener if the tuning rail can glitch. Also ensure the diode stays reverse biased across the full RF swing: forward conduction during negative RF half-cycles generates harmonics and intermodulation.
Place the varactor directly at the inductor with the shortest possible loop, and reference its bottom-side pad to a continuous ground plane. Use no-clean or RMA flux profiles compatible with the small SOD-523 leads and verify solderability with a stencil aperture of about 90% of pad area to avoid solder bridging on the 0.65 mm-pitch outline. Because NXP ships minimum 3000-piece reels, order cut tape from distributors for prototypes.
Compliance Information
The ,115 ordering suffix denotes NXP standard packing; explicit RoHS/REACH declarations were not present in the provided verified data and must be confirmed on the NXP product page.
