LISN: 50 Amps for Automotive

• Product Name: Line Impedance Stabilization Network (LISN)
• Specification: CISPR 25 (Automotive EMC Testing) / ANSI C16-1-2
• Application: Power Line conducted emission tests
• Frequency Range: 100 KHz - 108 MHz
• RF Connector: 50 Ohms N-type (female)
• Current Rating: 50 Ampere AC, 35 Ampere DC
• Voltage Rating: 270 VAC (Line to Ground), 380 VDC
• Inductors: 5 microhenry (air-core)
• Mains & EUT Connections: Superior Electric SUPERCON shrouded sockets
• Dimensions (each network): 13 x 7 x 7 inches / 33 x 17.7 x 17.7 cm
• Weight (each network): 14 lbs. / 6.3 kg
• Insertion Loss: < 1 dB (100 kHz to 108 MHz)
• Isolation: > 20 - 40 dB (100 kHz to 3 MHz), >40 dB (3 MHz to 30 MHz)

LI-550C CISPR 25 / CISPR 16-1-2 Automotive Single-Phase LISN FAQs

What is the LI-550C and what type of testing is it designed for?

The LI-550C is a single-conductor, 50Ω, 5 μH Line Impedance Stabilization Network (LISN) designed for power-line conducted emissions compliance testing of vehicle components per CISPR 25 and CISPR 16-1-2. It provides a defined, stable impedance on the vehicle power line, isolates the EUT from power source influences, and couples disturbance voltages to the RF measurement port. The LI-550C is the standard LISN for automotive and vehicle component EMC testing, covering powertrain control modules, infotainment systems, telematics units, EV drive electronics, and ADAS components whose conducted emissions on the vehicle power bus must meet vehicle manufacturer and regulatory requirements.

What standards does the LI-550C comply with and what do those standards govern?

The LI-550C is compliant with CISPR 25 (limits and measurement methods for protection of vehicle receivers from conducted and radiated emissions of vehicle components) and CISPR 16-1-2 (specifying LISN requirements). The LI-550C is accepted by automotive OEM EMC test laboratories, Tier 1 supplier test facilities, and accredited third-party automotive EMC laboratories worldwide for CISPR 25 and OEM-derived automotive component conducted emissions compliance.

What is the frequency range of the LI-550C and why does automotive CISPR 25 testing cover a different range than commercial CISPR 16-1-2?

The LI-550C covers 100 kHz to 108 MHz. The CISPR 25 range covers the AM broadcast band (530 kHz to 1.7 MHz) and FM broadcast band (76–108 MHz) to protect vehicle radio receivers from conducted interference generated by vehicle electronics. The 100 kHz lower limit provides margin below the CISPR 25 LW/MW band start, and the 108 MHz upper limit covers the full FM broadcast band.

Why does the LI-550C use a 5 μH inductor instead of the 50 μH used in commercial CISPR 16-1-2 LISNs?

CISPR 25 specifies a 5 μH LISN network for vehicle component conducted emissions testing. The 5 μH network is appropriate for vehicle DC power systems (12 VDC, 24 VDC, 48 VDC, or up to 380 VDC) with very low source impedances, reaching the 50 Ω asymptotic impedance at lower frequencies than the 50 μH commercial LISN. Using a 50 μH LISN for CISPR 25 testing would produce an incorrect impedance profile for the vehicle power bus environment, rendering measurements non-compliant.

What is the current rating of the LI-550C and what class of vehicle components does it support?

The LI-550C is rated at 50 A AC and 35 A DC. The DC rating is particularly relevant for automotive applications. This supports powertrain control modules, engine management systems, electric power steering controllers, body control modules, HVAC control units, infotainment head units, telematics modules, ADAS processing units, 12 V DC-DC converters, and EV battery management systems interfacing to the 12 VDC auxiliary bus.

What is the voltage rating of the LI-550C and what vehicle power systems does it support?

The LI-550C is rated at 270 VAC line-to-ground and 380 VDC. This supports 12 VDC conventional vehicle power, 24 VDC commercial vehicle systems, 48 VDC mild hybrid systems, and DC bus voltages up to 380 VDC. The 380 VDC rating covers the lower end of the EV high-voltage bus range; higher-voltage 400–800 VDC EV systems require specialized high-voltage automotive LISNs.

The LI-550C is sold as a pair. Why is a pair required and how are they connected in a vehicle DC power configuration?

CISPR 25 testing requires a LISN in series with each current-carrying conductor simultaneously. One LI-550C is installed in series with the positive supply conductor and one in series with the ground/negative return. The measurement is performed one conductor at a time; the inactive RF port is terminated at 50 Ω. Both conductors must be tested per CISPR 25 for complete characterization.

What type of connectors does the LI-550C use?

The LI-550C uses Superior Electric SUPERCON® shrouded sockets at both mains and EUT ports, with color-coded plugs included. The shrouded design protects against accidental contact with live conductors in DC automotive test setups carrying continuous high current, and color coding prevents polarity reversal errors.

Why is the mounting plate of the LI-550C left unpainted and what grounding is required?

The unpainted mounting plate enables a low-impedance metal-to-metal bond to the CISPR 25 reference ground plane, which represents the vehicle chassis ground. LISN internal capacitors create leakage current paths between power bus conductors and the chassis that must return through a defined low-impedance path to the reference ground plane, replicating the electrical environment of an actual vehicle where the chassis is the common ground reference.

What RF connector does the LI-550C use and what should be connected to the RF measurement port?

The LI-550C uses a 50 Ω N-type female RF connector, connecting via 50 Ω coaxial cable to an EMI receiver configured for CISPR 25 scanning from 100 kHz to 108 MHz. The inactive LISN RF port must be terminated at 50 Ω. Com-Power recommends a Transient Limiter — particularly important in automotive DC environments where relay switching, motor commutation, and power supply startup generate significant transient content.

What insertion loss and isolation does the LI-550C provide?

The LI-550C provides insertion loss below 1 dB from 100 kHz to 108 MHz. Isolation is above 20–40 dB from 100 kHz to 3 MHz and above 40 dB from 3 MHz to 108 MHz. In the LW/MW broadcast band measurements (100 kHz to 1.7 MHz), the lower isolation below 3 MHz must be considered to ensure results reflect only EUT emissions and not supply-conducted interference with insufficient attenuation.

How is the LI-550C individually calibrated and what calibration data is supplied?

Every LI-550C is individually calibrated per CISPR 25 and CISPR 16-1-2. Impedance, phase, isolation, and insertion loss data across the full 100 kHz to 108 MHz range are supplied with a certificate of calibration, verifying the impedance characteristic against CISPR 25 tolerance limits and providing accurate insertion loss corrections.

What is the warranty coverage for the LI-550C?

The LI-550C carries a three-year warranty from Com-Power Corporation. Periodic recalibration on a one- or two-year interval is recommended for automotive OEM and Tier 1 supplier test laboratories, particularly those operating under ISO/IEC 17025 accreditation.

What are the physical dimensions and weight of the LI-550C?

Each LI-550C network measures 15 x 7.5 x 7.5 inches (38 x 19 x 19 cm) and weighs 6.5 lbs (3 kg). A complete vehicle DC bus installation requires space for both units on the reference ground plane with current-rated cable routing to the DC supply and vehicle component EUT power connector, plus a coaxial cable to the EMI receiver.

What is a Transient Limiter and why does Com-Power recommend one with the LI-550C?

In automotive DC environments, relay switching, motor commutation, and power supply startup generate significant voltage transients. A Transient Limiter between the LI-550C RF port and the EMI receiver clamps transients before they reach the receiver, provides 10 dB attenuation and impedance matching, and incorporates low-pass and high-pass filter sections attenuating out-of-band emissions outside 100 kHz to 108 MHz.

How does the LI-550C differ from commercial 50 μH LISNs such as the LI-125C and LI-150C?

The LI-550C (5 μH, CISPR 25, 100 kHz–108 MHz) and the LI-125C/LI-150C (50 μH, CISPR 16-1-2/ANSI C63.4, 150 kHz–30 MHz) serve entirely different test regimes and cannot substitute for each other. The 5 μH and 50 μH networks produce fundamentally different impedance profiles. CISPR 25 requires the 5 μH network for the vehicle power bus environment; CISPR 16-1-2 requires the 50 μH V-network for the commercial mains environment. Using the wrong LISN renders test results non-compliant.

How does the LI-550C relate to the LI-3100 for CISPR 25 testing?

Both are compliant with CISPR 25. The LI-550C (50 A DC, 5 μH, 100 kHz–108 MHz) is appropriate for standard-power vehicle components up to 35 A DC. The LI-3100 (100 A forced-air cooling, 5 μH, 10 kHz–400 MHz, also DO-160/MIL-STD-461F/CISPR 16-1-2) is required for high-power vehicle components drawing up to 100 A, for programs requiring extended lower frequency coverage to 10 kHz, or for multi-standard programs including DO-160 or MIL-STD-461F.

What types of equipment cannot be tested with the LI-550C?

The LI-550C is not suitable for: equipment exceeding 35 A DC or 50 A AC (use LI-3100); 400–800 VDC EV high-voltage bus systems (specialized high-voltage automotive LISNs required); commercial CISPR 16-1-2 / ANSI C63.4 testing (use LI-125C or LI-150C); DO-160 avionics testing (use LI-325C, LI-350, or LI-3100); or MIL-STD-461 defense testing (use LI-325C, LI-350, LI-400C, LI-4100, or LI-3100).

How is the LI-550C used in CISPR 25 conducted emissions testing of an automotive infotainment head unit?

The LI-550C pair is installed on the CISPR 25 reference ground plane. A regulated 13.5 VDC bench supply (representing nominal 12 VDC vehicle charging voltage) connects to the mains inputs. The head unit connects to the EUT outputs and is operated in typical modes: radio reception, navigation, media playback, and hands-free call. Conducted emissions are measured from 100 kHz to 108 MHz on the positive supply conductor with peak and quasi-peak detectors per CISPR 25, compared against the vehicle OEM’s CISPR 25-based component specification limits — which may be more stringent than published CISPR 25 Class 5 limits.

What is a real-world CISPR 25 test scenario using the LI-550C for an EV DC-DC converter?

An EV onboard DC-DC converter stepping down 400 VDC to the 12 VDC auxiliary bus can draw up to 35 A on the 12 VDC output side. The LI-550C pair is installed between the converter’s 12 VDC output and the auxiliary bus load. Conducted emissions from 100 kHz to 108 MHz at several load levels are compared against CISPR 25 limits. The LI-550C’s 35 A DC rating accommodates full rated output current, capturing worst-case switching frequency harmonics and their potential impact on AM and FM vehicle radio reception.

How does an automotive EMC engineer use the LI-550C during pre-compliance testing of a new ADAS radar front-end module?

During development of a 77 GHz ADAS radar front-end module, the LI-550C provides the CISPR 25 standardized platform for pre-compliance screening. The radar module is powered through the LI-550C pair and a spectrum analyzer scans 100 kHz to 108 MHz with the radar in normal detection mode. The engineer compares the conducted emissions envelope against CISPR 25 Class 5 limits to identify switching frequency harmonics of the power management circuitry falling in or near the FM broadcast band (76–108 MHz), where vehicle radio reception is most sensitive. Pre-compliance findings drive power supply filtering changes before formal qualification, reducing OEM supplier qualification failure risk.

How is the LI-550C applied when testing automotive components to OEM-specific EMC standards that reference CISPR 25?

Major automotive OEMs (Ford, GM, Volkswagen Group, Toyota, and others) publish component EMC specifications referencing CISPR 25 but may add OEM-specific requirements such as tighter limits, additional frequency bands, or specific operating modes. These specifications uniformly require the CISPR 25 5 μH LISN for conducted emissions measurements, meaning the LI-550C is the required LISN for all CISPR 25-based OEM component tests. The LI-550C’s individual calibration certificate and CISPR 25/CISPR 16-1-2 compliance ensure it meets the LISN requirements of all major automotive OEM component specifications without substitution or qualification by exception.