ISO 7637-2 Pulse 1
Conducted Immunity to Transients on battery lines.
Pulse 1 (Us = -150V, Ri = 10Ω, td = 2 ms, tr = 1µs, t1 = ≥ 0.5s (repetition rate), t2 = 200 ms, t3 < 100µs) can upset functionality of electronic modules. Most automotive OEM specs are accepting Class B response (DUT self-recoverable deviations), others are asking Class A response (no deviations) during Pulse 1.
In this particular case the pass/fail criteria was Charging Voltage remains 5V ±0.5V for 12V Battery dropouts ≤ 500µs. The EMC test plan asked the use of DMM to monitor the USB charging function for a Class A expected response:
- This was a simulation of a mobile phone charging event.
- DMM can only detect 5V Charging Voltage dips/drops ≥ 250 µs. A FLUKE can be set to count MAX and MIN voltage peaks, otherwise to monitor 5V fast voltage fluctuations is not practically possible.
- The EMC test plan allowed the use of oscilloscope only for information.
Download this movie to see how the charging function was monitored simultaneously on both oscilloscope and DMM:
5V_Charging_during_P1.mp4 (127.57 mb)
A similar monitoring equipment limitation was imposed the EMC Test Plan for dropouts test. Download this movie to see how the charging function was monitored simultaneously on both oscilloscope and DMM:
5V_Charging_during_500_microSec_dropout.mp4 (30.91 mb)
Christian Rosu, Nov 8, 2021