How to avoid USB-C connector overheating

How to avoid USB-C connector overheating

With the widespread use of the USB Type-C interface, which supports higher USB transmission standards and charging speeds, its safety is a growing concern. USB-PD uses a Type-C interface form with a maximum current of 5A.

From a safety perspective, USB-C cables must be able to carry the appropriate voltage and current. For chargers with tethered or fixed cables, the cable must be able to handle the maximum voltage output of the charger. Cables with USB-C plugs on each end must be able to handle 21 V and at least 3 A. Cables containing special electronically marked ICs can carry 5 A of current. Any equipment placed in the power path, especially protective equipment, must also be able to withstand these levels of voltage and current.

USB Type-C connectors with small contact pitch (0.5mm) are more susceptible to dirt and dust contamination, which can lead to resistive failures between power and ground. Combined with the higher power on the Vbus line, USB connectors are at greater risk of overheating, which can damage connectors, cables, and connected port electronics. Increased temperatures can melt the connector or, in the worst case scenario, start a fire.

Traditional methods of preventing USB cable overheating include placing a polymer positive temperature coefficient (PPTC) device or a miniature circuit breaker (also known as a thermal fuse) on the VBUS power cable. The selected device will be placed on the printed circuit board inside the connector to detect temperature increases caused by resistor failures.

One of the disadvantages of adding protection devices to the power path is that their resistance, even if only a few milliohms, can lead to charging power losses and thus reduce efficiency requirements. 

The enclosed range of the USB-C connector also makes it difficult to install protection devices inside. PPTCs for protecting 60 W chargers are 3.2 × 2.5 mm in size, while miniature circuit breakers are usually larger. PPTCs and miniature circuit breakers for the protection of 100 W need to be larger. In addition, the mechanical structure of miniature circuit breakers is relatively weak, and the cable assembly process may deform the bimetallic materials that make them up, which will prevent them from providing protection during heating faults.

One way to address these shortcomings is to place a different type of protection device in the communication channel (CC) of the USB-C connector, rather than on the V BUS line. There is a compact (2.0 × 1.2 mm) PolySwitch setP digital temperature indicator. The setP device detects an increase in temperature and then "alerts" the system to power down. When the temperature indicator detects a temperature of 100° C or higher, its resistance increases dramatically.

The temperature indicator is placed in the configuration channel line. It is not placed in the Vbus line, so it does not reduce any voltage or power, nor does it reduce the capacity of the supply on the Vbus line. If the component detects a temperature of 100°C, its resistance increases significantly. the USB protocol interprets the high resistance as an open connection between the source connection, the Vbus and receiver connections, and the load, and the Vbus line is deactivated.

When the condition causing the overheating is corrected and the sensor temperature drops below the 100°C threshold, its resistance is reset to a low temperature value of about 10 Ω and the Vbus is re-energized. For best results, a temperature indicator should be built into the USB plug and/or socket to monitor the connector temperature at the source of the fault.

Unlike positive temperature coefficient devices or small circuit breakers that must be in the Vbus line, digital temperature indicators do not consume power and reduce power delivery capability. In addition, these other components are limited to 100 W and lower, which will prevent them from being used in USB Type-C applications with extended power ranges.

The size of the temperature sensor should be small enough to allow detection at the source of the fault. It should also be able to change its resistance state in as little as one (1) second to prevent damage to cables and electronic components. The diagram below shows how a temperature indicator can maintain a safe connector surface temperature during an overheat fault.

By HornmicLink_Henry @230427 21:16