In smartphone PCB design, these components need to be considered for ESD protection

In the design of smart phone products, the following interfaces or components need to be considered for ESD protection: SIM card interface USB interface Headphone interface MIC Receiver Speaker LCD charging interface Micro SD interface Serial port battery interface According to the ESD status of different interfaces, the protection level is divided.

In the design of smart phone products, the following interfaces or components need to be considered for ESD protection: SIM card interface USB interface Headphone interface MIC Receiver Speaker LCD charging interface Micro SD interface Serial port battery interface According to the ESD status of different interfaces, the protection level is divided.

Protection level 1: ESD protection must be carried out on the hardware

Protection level 2: ESD protection is recommended

1. ESD protection of battery interface The temperature detection signal of battery interface device can be protected by common varistor. In addition to the TVS for protection, a 100μF capacitor needs to be added near the battery power supply.

2. 2. ESD protection of SIM card interface The VCC overcurrent of the SIM card is small, and the same protection device can be used with other signals of the SIM card. The signal speed of the SIM card is low, and it is generally not hot-swappable, and the electrostatic protection level can be slightly lower. Minimize surface traces during PCB design.

3. 3. ESD protection of SD interface The SD card interface protection device should be grounded as close as possible to the pins of the card holder. When detecting card insertion and removal through the mechanical structure of the card holder, the SD_DETECT signal will have burrs on the edge due to the inherent reasons of mechanical contact. The hardware can connect a capacitor of about 10pF in parallel near this signal, and debounce in the software.

4. ESD protection of USB interface The USB_D+ and USB_D- signals need to protect the parasitic capacitance of the device less than 3pF, while the VBUS signal and the Charge signal are multiplexed, requiring protection devices with high power and strong overcurrent capability. The ESD protection of these three signals is recommended to use special protection devices for the USB interface.

5. ESD protection of LCD interface and Camera If the LCD interface is enclosed in the structure like the reference design, it is less likely to be affected by ESD. For ESD protection, the FPC (Flexible Printed Circuit) of the LCD needs to be well grounded. to ensure reliable grounding. If the LCD is directly exposed to the human body, ESD/EMI devices need to be added to the LCD interface for protection.

6. The ESD protection audio signal of the headphone jack is a low-frequency analog signal, and the current is small. There is no specific requirement for the parasitic capacitance of the protection device. The ground pins and shielding ground pins of the headphone jack need to be drilled to the main ground nearby. In addition, it is necessary to protect the space interference of high-speed and high-frequency signals on the PCB board (high-speed and high-frequency signals need to be protected by a shielding cover or inner layer wiring) to avoid EMI problems and affect audio signals through certain coupling methods. ESD protection devices should be placed as close as possible to the headphone pins.

7. The ESD protection of other audio interfaces has no direct contact point in the structural shell, but there are structural holes outside, which may be affected by air discharge, so ESD protection treatment is still required. Because the signal characteristics are the same as the headphone signal, ESD treatment can also use TVS tubes or varistors with the headphone jack. In addition, when designing the structure, try to increase the path of external static electricity to the internal pins, which is also very helpful for ESD protection.

The Links:   CAT25050U NL8060BC31-41C LCD-SOURCE

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