Page 11 - EngineerIT June 2022

ELECTRONICS

USB-C power delivery data lines

demand enhanced protection

By Nazzareno (Reno) Rossetti and Josh Fankhauser

USB-C and USB-C power delivery raise voltage and power levels. A new reversible connector with tighter pin pitch than that of
USB Micro-B, increases the risk of short circuits. This, in conjunction with the ever increasing complexity of portable devices
leads to enhanced ESD, surge and overvoltage protection requirements. In this design solution we propose a compact, fully
featured protection IC that can lead to a dramatically lower BOM and smaller PCB space occupancy.

Introduction
The new USB Type-C® (USB-C) cable and connector specification is
dramatically simplifying the way we interconnect and power our
electronic gadgets such as digital cameras and ultra-thin tablets
(Figure 1). The specification supports USB-C charging applications up
to 15W, and the USB-C power delivery (PD), which extends charging
up to 100W, includes a wide variety of different devices that can be
interchangeably charged. With USB Type-C come new challenges in
protecting the system. The new connector has a smaller pitch than
that of the USB Micro-B, which leads to increased risk of mechanical
shorts to VBUS. Additionally, due to the high voltages associated
with USB PD, more robust protections are needed. And finally,
the ever increasing complexity of the electronic loads demand
enhanced protection from ESD and voltage surges. This design
solution reviews the USB Type-C PD architecture and the challenges
associated with D+/D- data signal protection. It then proposes a
highly integrated 2 x SPDT switch that can address these challenges
with minimum BOM and PCB occupancy. Figure 1: A digital camera connected to a tablet via a USB-C cable.

USB-C PD System
Figure 2 illustrates a typical portable power management device
front-end equipped to connect to a USB-C cable and powered by a
lithium-ion (Li+) battery.
When the VBUS is present, it powers the charger, the system,
and the rest of the blocks. In this phase, the battery is charged. When
the VBUS is disconnected, the battery powers the system. With the
USB-C cable, the CC1 and CC2 pins determine port connection, cable
orientation, role detection and port control. The D+/D- lines are the Figure 2: USB PD power management system.
standard USB-C communication lines handling data with a speed of
480Mbps and are protected by the D+/D- protection device. The PD dump is a surge generated by cutting the battery connection off
controller implements the power delivery protocol. on an automobile. A good data line protection IC should offer
adequate protection without significant data degradation.
The Protection Challenge
Electric surges and electrostatic discharges (ESDs) in a power supply Integrated Solution
are common and can interfere with or cause damage of electronic As an example, the MAX20334 is a 2 x SPDT switch with
loads and equipment. ESD is caused by the transfer of static overvoltage protection intended for use with portable devices
electrical charge from a body to an electronic circuit and is a big (Figure 3). The IC is designed to protect the downstream data
concern for handheld electronics. Surges can be caused by lightning line from a high-voltage short, ESD, or surge event. The device
or induced in long cables lying close to a lightning strike. Switches combines low on-capacitance and low on-resistance necessary for
or relays can cause surges during on and off operation. And a load high-performance switching applications in portable electronics.

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