CISPR 25
Understanding CISPR 25
Modern vehicles contain 50 to 150 electronic control units (ECUs), multiple electric motors (HVAC, seat, window, power steering, EV traction), high-frequency switching power converters, LED lighting drivers, and infotainment systems. Each generates broadband electromagnetic emissions that can interfere with the vehicle's own receivers: AM radio (530 kHz to 1.7 MHz), FM radio (76 to 108 MHz), DAB+ (174 to 240 MHz), GPS/GNSS (1.2 to 1.6 GHz), cellular (700 MHz to 2.5 GHz), Bluetooth/WiFi (2.4 GHz), and V2X (5.9 GHz). CISPR 25 establishes the emission limits that each individual component must meet to prevent degradation of these receivers.
The standard defines a test setup specific to the automotive environment: the device under test (DUT) is mounted on a ground plane in a shielded enclosure, powered through an artificial network (AN) that presents a defined DC supply impedance simulating the vehicle battery and wiring harness. Conducted emissions are measured on power supply and signal lines using the AN as the measurement point. Radiated emissions are measured at 1 m distance with rod antennas (150 kHz to 30 MHz), biconical antennas (30 to 200 MHz), log-periodic antennas (200 to 1,000 MHz), and horn antennas (1 to 2.5 GHz). The five severity classes provide approximately 6 to 10 dB steps between each level, with OEMs selecting the class based on the component's installation location and the sensitivity of nearby receivers.
CISPR 25 Test Parameters
d = 1 m (component-level, shielded room)
Power Supply:
Vdc = 13.5 V (12V system) or 27 V (24V) or 48 V (mild hybrid)
Severity Step Between Classes:
Δ ≈ 6 to 10 dB per class level
AN impedance: 5 Ω + 1 μH per CISPR 25 Annex A. Frequency bands align with AM, FM, DAB, cellular, GPS receiver services. Peak and quasi-peak detectors used.
CISPR 25 Severity Classes
| Class | Stringency | Typical Application | Example Limits (FM band) |
|---|---|---|---|
| Class 1 | Most relaxed | Engine bay, far from antennas | ~42 dBμV/m at 1 m |
| Class 2 | Relaxed | Underbody, trunk | ~36 dBμV/m at 1 m |
| Class 3 | Moderate | General electronics | ~30 dBμV/m at 1 m |
| Class 4 | Strict | Dash, pillar-mounted | ~24 dBμV/m at 1 m |
| Class 5 | Most stringent | Near antenna, head unit | ~18 dBμV/m at 1 m |
Frequently Asked Questions
Why does CISPR 25 have five severity classes?
Components at varying distances from antennas need different limits. Class 1 (engine bay, far from antennas) is most relaxed; Class 5 (near antenna modules, infotainment) is most stringent (~24 dB difference). OEMs specify the class per component based on mounting location and receiver proximity. Most OEMs default to Class 3+ for general electronics.
How does CISPR 25 testing differ from CISPR 22/32?
CISPR 25 uses automotive-specific setup: 12V/48V DC supply through an artificial network (not LISN), 1 m radiated measurement distance (vs 3 to 10 m), and frequency bands aligned with vehicle receivers (AM/FM/DAB/GPS/cellular). The shielded room represents vehicle body. Test methods are designed for component-level qualification.
How does CISPR 25 relate to OEM standards?
CISPR 25 is the baseline; OEMs add stricter or additional requirements. Ford CS-2009, GM GMW3097, VW TL 81000, BMW GS 95024 all reference CISPR 25 methods but add immunity, ESD, and transient testing. EV components face 6 to 10 dB stricter limits for high-voltage conducted emissions at 150 kHz to 30 MHz.