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LQW32FT470M0H: An Automotive PoC Bias-T Inductor
11/4/2026 12:34:18 AM
LQW32FT470M0H: An Automotive PoC Bias-T Inductor
1. Positioning
The LQW32FT470M0H is a wirewound ferrite inductor from Murata's LQW32FT series, housed in a 1210 (3225 metric) package with 47μH ±20% inductance, AEC-Q200 qualification, and an operating temperature range of −40°C to +125°C. Its core application is not ordinary power filtering or DC-DC conversion, but the PoC (Power Over Coax) circuit in automotive high-speed interfaces.
The goal of PoC is to carry both high-speed serial data and DC power on a single coaxial cable, typically between an onboard camera and a processing unit: data travels from camera to processor, and power travels from processor to camera. This requires a Bias-T network inserted between the signal path and the power path, presenting high impedance to the high-frequency signal and low impedance to DC. The LQW32FT470M0H is the inductive element at the heart of that Bias-T network.
2. Why One Inductor Can Replace Several
In earlier PoC implementations, maintaining high impedance across a wide band while separating signal and power required multiple inductors of both large and small values-a large inductance for high impedance at lower frequencies, and a small inductance for high impedance at higher frequencies. The key advance of the LQW32FT series is that a single 47μH inductor provides sufficient high impedance across a wide band (typically covering 4MHz to 1GHz), replacing the multiple components previously required. The direct benefits are reduced system size, saved board space, and lower total DC resistance.
Achieving 47μH in a 1210 package is a relatively high density for a wirewound ferrite construction. The minimum self-resonant frequency of 30MHz means the component continues to present inductive impedance across a broad portion of the PoC band, rather than entering the capacitive region at a lower frequency and losing its isolation effect.
3. Key Specifications
| Parameter | Specification |
|---|---|
| Manufacturer | Murata Electronics |
| Series | LQW32FT_0H |
| Inductance / Tolerance | 47 μH ±20% |
| Inductance Test Frequency | 1 MHz |
| Rated Current (Isat, based on inductance change) | 300 mA |
| Rated Current (Itemp, based on temperature rise) | 500 mA (85°C ambient) / 100 mA (125°C ambient) |
| Maximum DC Resistance (DCR) | 0.90 Ω |
| Minimum Self-Resonant Frequency (SRF) | 30 MHz |
| Package / Size | 1210 (3225 Metric) / 3.2 × 2.5 × 2.3 mm |
| Core / Construction | Ferrite core, wirewound |
| Operating Temperature | −40°C to +125°C |
| Automotive Qualification | AEC-Q200 |
| Typical Applications | Automotive PoC Bias-T circuits; onboard SerDes interfaces |
4. The Engineering Meaning of Two Current Ratings
The datasheet provides two current ratings that correspond to different limiting mechanisms, and both must be satisfied in a design. The first is Isat = 300mA, based on inductance change: when 300mA DC is applied, the inductance is allowed to deviate from nominal by up to ±30%. The second is Itemp, based on temperature rise: 500mA at 85°C ambient, derated to 100mA at 125°C ambient, with the constraint that self-heating does not exceed a 40°C rise.
This means that in a high-temperature environment-for example, a camera module near the engine bay-the usable current is far lower than the 85°C figure. The 100mA limit at 125°C is not a "performance reduction" but the natural contraction of the thermal margin at elevated ambient. The current flowing in the PoC power path (typically the camera module's supply current) must be verified against this rating at the worst-case temperature.
5. Questions and Answers
Q: What exactly does the LQW32FT470M0H do in a PoC circuit?
A: It is the isolation inductor in the Bias-T network. PoC superimposes DC power and high-speed serial data on a single coaxial cable. The Bias-T creates a frequency-selective connection between the signal path and the power path: low impedance to DC, allowing power through; high impedance to the high-frequency signal, preventing signal energy from leaking into the power network. The 47μH value provides this high impedance across a wide band, allowing a single component to cover the frequency range that previously required a combination of large and small inductors. In Murata's Bias-T design examples, this device often serves as L2, paired with an L1 such as the LQW18CNR65J0H.
Q: Why is the rated current only 100mA at 125°C while it is 500mA at 85°C?
A: This is temperature-rise-based derating. One constraint on rated current is that self-heating must not cause a temperature rise exceeding 40°C. At a 125°C ambient, most of the allowable temperature budget is already consumed by the environment, so the current must be reduced to keep the junction (ambient plus self-heating) below the 125°C limit. At 85°C, the environment consumes less margin, allowing a higher current. The two ratings work together: Isat (300mA) prevents excessive inductance drop, while Itemp (temperature-dependent) prevents overheating.
Q: What does the 30MHz minimum SRF mean for PoC applications?
A: SRF is the frequency at which the inductor resonates with its own parasitic capacitance. Below 30MHz, the component presents inductive impedance; above 30MHz, parasitic capacitance gradually dominates and the impedance departs from pure inductive behavior. PoC high-speed serial signals (such as automotive SerDes) have fundamental and harmonic content extending to higher frequencies. The 30MHz minimum SRF ensures that across the low-to-mid portion of the PoC band where isolation is required, the inductor still provides effective blocking impedance. Murata's impedance-versus-frequency curves should be consulted to confirm that impedance in the actual signal band meets the Bias-T isolation requirement.
Q: Does AEC-Q200 qualification mean it can be used in any automotive location?
A: AEC-Q200 confirms that the part has passed automotive stress qualification for passive components, but location-specific suitability also depends on temperature, vibration, and reliability requirements. The LQW32FT470M0H's 125°C ceiling and ferrite wirewound construction make it suitable for camera modules, SerDes interface nodes, infotainment, and comfort equipment. Extreme high-temperature or high-vibration locations still require additional evaluation against the specific environment.
6. Conclusion
The value of the LQW32FT470M0H is not a generic label like "high inductance" or "high current." It lies in using a single 1210-sized, 47μH ferrite wirewound inductor to provide the Bias-T isolation impedance across a wide band, replacing multiple inductors that were previously necessary. The dual current ratings (Isat 300mA / Itemp derated with temperature) and the 30MHz minimum SRF define its engineering boundaries. For automotive SerDes designs that need PoC signal-power separation in a compact footprint, it offers a single-component solution validated to AEC-Q200.
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