Leiditech EMC Expert Team Rectification Cases
A.Chip-level EMC case presentation:
1. A high-voltage ESD protection scheme using a multi-state MOS to assist in triggering a SCR
2. Leakage suppression and electrostatic protection techniques in the chip transmission pressure circuit
B.Consumer Electronics
EMC technical training for communication base stations, consumer products, etc.
Led the development of enterprise standards related to mobile phone EMC, including EMC testing standards for smartphones/tablets, RF desense testing standards for smartphones/tablets, and participated in establishing standards for RF carrier interference resistance testing for smartphones/tablets/cameras, as well as standards for RF carrier interference resistance testing of display touch controls on smartphones/tablets.
Led the formulation of grounding design specifications for mobile phone EMC, and participated in developing normalized circuit design specifications for mobile phone EMC.
Responsible for hardware protection against RF carrier interference for displays, improvement of CPU shielding solutions, optimization of charging EMC performance, and multiple specialized technical research projects relating to desense and user experience correlation.
1. Problem Description: Contact with 10KV, electrostatic discharge to USB ID, causing screen not to light up.
Failure Cause: Electrostatic charge passed through the 1K resistor of the USB ID, and then discharged to the adjacent 0R resistor. The 0R resistor supplies power to the screen IC, causing the screen IC to be damaged.
Optimization Plan:
Plan One: Add TVS diodes to the USB ID;
Plan Two: Move the 0R resistor away, keeping it far from the 1K resistor.
2. Problem Description: After the product was launched, there was a problem of system freeze.
Failure Cause: Antenna signal coupled to the T card signal line. The T card signal line inside the CPU and the CPU reset line overlapped, causing system freeze.
Improvement Plan: Reduce the RF transmission power and optimize the internal wiring of the chip simultaneously.
3. Problem Description: A handheld device, air 12KV caused the single unit of the SIM card to be damaged.
Failure Cause: Electrostatic charge entered the SIM card slot gap and pressed into the material hole of the card tray, resulting in secondary discharge, causing the single unit of the SIM card to be damaged.
Optimization Plan: Extend the metal frame outward beyond the material hole.
C.Power supplies, new energy batteries;
D.Automotive electronics;
Led the formulation of EMC-related enterprise standards, including the EMC test standards for complete electric motorcycles, the EMC grounding design specifications for complete electric motorcycles, the EMC test standards for key components of electric motorcycles (inverter/VCU/BMS/T-Box, etc.), and the EMC design specifications for key components of electric motorcycles (inverter/VCU/BMS/T-Box, etc.).
4.1 Problem Description: The inverter RE of the heavy-duty electric motorcycle exceeds the standard, the VCU restarts due to DC-DC interference, the Bluetooth of the T-Box drops out due to DC-DC interference, and the GPS search time is too long, etc., these are major critical problems.
Optimization Plan: By using Octve + openEMS tools, a series of detailed characteristics and design options for suppressing EMI interference through the grounding system were successfully established.
Responsible for the EMC research and development design, debugging, rectification, and certification of the DC-100 model heavy-duty electric motorcycle.
E.Electric power industry；
5.1 EMC Technical Guidance: Responsible for providing necessary EMC technical training to the base station maintenance and technical support departments, including the improvement of the SC4840 MCC (Multi Channel Card) board, the troubleshooting of SC4812 BBX (broadband transceiver) alarm issues, and the resolution of UMTS base station ESD problems, etc.
5.1 EMC Technical Guidance: Responsible for providing necessary EMC technical training to the base station maintenance and technical support departments, including the improvement of the SC4840 MCC (Multi Channel Card) board, the troubleshooting of SC4812 BBX (broadband transceiver) alarm issues, and the resolution of UMTS base station ESD problems, etc.
F.Military aerospace products;
G.Large medical appliances;
Certification, registration consultation, commissioning test, proxy testing, overseas testing.
1. Electric bone knife
The metal part of the bone knife handle, ESD discharge voltage is 6Kv. When the motor stops, the main control reports an error.
Rectification measures: For the UVW phase of the bone knife motor, add an amorphous magnetic inductor for filtering, and connect a 10uF filter capacitor in parallel with the MOS tube half-bridge driver chip.
2. Hysteroscopic ESD indirect discharge coupling board with 6kV image loss
After confirmation, it was found that the MIPI communication of the front-end digital CMOS was interfered with.
Measures: Change the FPC ribbon cable of the lens to a multi-layer structure. The two external layers are connected to the GND of the acquisition board's GND. After the rectification, the ESD 8kv indirect discharge is ok.
3. Acupoint electrical stimulation device, electrode plate connected to ESD touch discharge, main unit restarts
Measures: Replace the application end isolation boost transformer. Add a shielding layer between the primary and secondary, and add a common mode inductor at the output end. The test is qualified.
4. Infrared therapy device
Infrared therapy device has air discharge of 15kv. EUT restarts or freezes. It requires power-off restart.
Measures: After confirmation, the "freezing" caused by ESD discharge is actually the failure of the serial port screen. The main control board is still working.
Measures: Use a reset watchdog chip for the serial port screen's main control chip. The ESD discharge causes the watchdog to output a reset signal, resulting in a restart phenomenon. The reason is that the watchdog chip is too close to the PCB edge and the filtering decoupling is insufficient. The chip is moved to the middle of the PCB and GND copper plating is added around it. The restart phenomenon disappears. Add ESD protection devices at the communication ends AB of the serial port screen. The freezing phenomenon no longer occurs.
EMC forward design and rectification, Leimao has dictionary-like accumulation, systematic EMC diagnostic analysis tools and methods, and is good at solving all kinds of difficult problems.
The products of Shanghai Leiditech Electronic Technology Co., Ltd. meet the relevant national testing standards and requirements, as well as international standards such as IEC.FCC, and have obtained UL, VDE, ROHS, REACH and other series of certifications. Leimao products can meet the requirements of high-standard lightning protection, overvoltage protection and overcurrent protection, thereby improving the service life of the core components of the circuit, and enhancing the flexibility and scalability of the end product.
