The human body moves to generate static electricity, and how does the wearable device circuit protection design?
Circuit protection techniques and board layout strategies help improve security, reliability, and connectivity. Wearable technology has a weakness that is unlikely to occur in the Internet of Things: the body generates static electricity while moving. Static electricity can damage sensitive electronic devices that support IoT applications.
To understand this problem, we started with the Human Body Discharge Model (HBM) and used to describe the sensitivity of integrated circuits to electrostatic discharge (ESD) damage. The most common HBM concept used is the experimental model defined in the military standard MIL-ST D-8 8 3 , Method 3015.8, Electrostatic Discharge Sensitivity Classification. A similar international HBM standard is JEDEC JS-001. Both the JEDEC JS-001 and the MIL-STD-883 simulate a charged human body with a 100pF capacitor and a 1.5kΩ discharge resistor. During the test, the capacitor was fully charged from 250 V to 8 kV and then discharged through a 1.5kΩ resistor in series with the device under test.
Since wearable devices are designed to be used snugly, they continue to suffer from electrostatic shocks caused by close interaction with the user. Without proper protection, the sensor circuit, battery charging interface, button or data input/output port of the wearable device may be damaged by electrostatic discharge (ESD) similar to that produced in the HBM test. Once the wearable device fails, the functionality and reliability of the entire network is also affected.
Advanced circuit protection technology and board layout strategies protect wearables and their users. Applying these recommendations early in the design process will help circuit designers improve the performance, security, and reliability of their wearable technology designs and help build a more reliable IoT.
1 Small package size, but ESD protection is not small One design challenge for wearable device circuit protection is that wearable devices are getting smaller and smaller. In the past, large structure diodes and large package sizes were required (eg
Figure 1 TVS diode two structures
Figure 2 IEC 61000-4-2 rating,
Designers should choose unidirectional diode configurations whenever possible because they perform better in negative voltage ESD strike events. During a negative voltage ESD strike, the clamp voltage will be based on the forward bias of the diode (typically less than 1.0 V). Conversely, the bidirectional diode configuration provides a clamp voltage that is based on the reverse breakdown voltage during a negative voltage surge and is higher than the forward bias of the unidirectional diode. Therefore, the unidirectional configuration can greatly reduce the pressure on the system during a negative voltage surge.
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