FEAT
ATURE INTERCONNECTION
Protecting USB-C cables against overheating Through the dev
eve higher lev eve vels of pow
velopment ofUSB Type-C (USB-C) andUSB Pow ower (up to 100W) can now
fromLittelfuse Inc. presents a new T
can charge different devices at the oday, consumers want cables that
appropriate power levels, as well as support higher data transfer rates. Therefore, many manufacturers have
any charging system: the charger, the Three devices must work together in embraced the USB C standard.
USB-C chargers have an AC plug on one cable and the device being charged.
on the other for plugging into the device either a cable with a USB-C connector end for plugging into a wall outlet and
that allows plugging in a USB-C cable to be charged or a USB-C output port
USB-C cables are equipped with one or (see figure 1).
more symmetrical 24-pin connectors.
appropriate voltages and currents. From They must be capable of carrying
with captive or fixed cables, these cables a protection standpoint, for chargers
Cables with Type-C plugs on each end charger’s maximumvoltage output. must be capable of handling the
3A. Those that include special e-marker have to be capable of 21V and at least
ICs can carry up to 5A of current. Any device placed in the path of power must also be capable of withstanding these voltage and current levels.
CAUSES OF CHARGING DAMAGE USB-C cables are susceptible to damage
that these cables must carry while using possible cause is the high level of power because of two reasons. The first
cause a thermal event. The second factor increases the risk of a fault that could spacing. The tight pin-to-pin spacing connectors with very tight pin-to-pin
contamination and the associated risk of is the connector’s susceptibility to
hair, metal particles or other debris gets uncontrolled overheating. When dust,
it could create a resistive fault fromthe stuck in a USB Type-C cable connector,
power line to ground. These resistive
temperature rise while increasing current faults can cause a dangerous
by only a minimal amount.
This was commonly a PPTC or a thermal BUS power line.
The old approach for protecting USB cables fromoverheating involves locating a device on the V
cut-off breaker. The chosen device is 12 MARCH 2019 | ELECTRONICS Figure 3:
PolySwitch setP digital temperature indicators help protect USB Ty
levels of USB Power Delivery
Type-
help protect the highest overheating. They can C plugs from
Figure 2:
Resistive faults in USB-C connectors can damage devices and cables during charging
PPTCs and mini-breakers both can contribute to power loss. This makes it
challenging to fit either device into the efficiency requirements. It can also be manufacturers to meet mandatory more difficult for power supply
close confines of a connector. For
protecting 60W chargers typically have example, the PPTCs suitable for
a 1210 (3.2 × 2.5mm) footprint. PPTCs and mini-breakers meant to protect 100W would have to be even larger. Finally, a mini-breaker has a relatively weak mechanical structure and its bi- metal materials can be deformed during the cable assembly process. In the case of a heating fault, this would prevent the mini-breaker fromproviding protection.
USB-C output ports Figure 1:
placed on a printed circuit board inside the connector to sense the temperature rise created by the resistive fault. But this approach can present some challenges to power supply design engineers, when attempting to protect up to 100W of power.
ewapproach for protect owe
owbe used by those samemobile devices. Todd Phillips ction, in response to the higher, leve
ev A NEW DESIGN APPROACH
of protection device in the communication disadvantages is to place a different type One possibility to address these
channel (CC) of the USB-C plug, rather than on the VBUS line. The newest device
designed to protect USB Type-C cables against the effects of over-temperature conditions is the compact PolySwitch setP digital temperature indicator (See figure 3). This device senses a temperature increase and informs the systemto shut down the power.
With the setP digital temperature
indicator placed on the CC line, it switches froma low resistance state to a high resistance state, when it senses
temperatures higher than 100°C. This increased resistance causes the voltage on the CC line to increase beyond the value defined by the USB Implementers Forum (USB-IF) known as the “vOpen” voltage. Because the voltage created by setP is higher than the specified vOpen value, the charging systemassumes the cable has become detached. The charging system
themturns off the power through the VBUS line. This prevents the connector, cable
and the device being overheating. The cab
le can resume normal charged from
operation, as soon as the user disconnects the cable and removes the debris fromthe connector.
The setP devices are well suited for use in power supplies with captive USB-C cables, USB Type-C charging cables and USB Power Delivery charging cables. The same device can be used to protect cables designed for 15W, 60W or 100W operation, allowing for simple part selection.
Mobile device users benefit froma fast, uncomplicated way to transfer data and charge their devices by USB-C cables. As the standard supports high power levels, appropriate protectio necessary. Now, with
werDelivery (USB-PD) specifications, ev
ry vel of risk
the development of n solutions are
a new approach to over-temperature protection, they can be confident that the process will remain safe. setP digital temperature indicators offer a small, energy-efficient solution, for protection against overheating.
Littelfuse Inc.
www.littelfuse.com T: +1 773-628-1000
/ ELECTRONICS
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