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Stuart Vance

Mar 25, 2015

Integrated
ESD Protection

ESD
Protection Diodes

TPD2E2U06

ESD

TPD3S014EVM

USB
2.0

Electrostatic
Discharge

TPD3S044

TPD3S014

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Related

How to protect USB host ports with ESD current-limit protection
devices

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One of the hottest topics regarding interface technology today is the
universal serial bus (USB) Type-C connector, popular for its reversibility,
higher data transfer, power delivery and additional protocols. While there is
much excitement over the new standard, the reality is that the USB Type-A
connector is still prominent and is being designed into end equipment today.
When designing for USB host ports, you should consider two major areas of
protection: overcurrent protection and electrostatic discharge (ESD)
protection.

Overcurrent protection

Per section 7.2.1.2.1 of the USB 2.0 specification, “All host and
self-powered hubs must implement overcurrent protection for safety reasons.” You
can accomplish this by using a fuse or current-limit switch. Moreover, a
current-limit switch is the preferred solution over a fuse because it allows you
to allocate less power per port during design. In a transient event, the load
switch limits the output current to a safe level by operating in constant
current mode. A fuse will allow the current to rise above the maximum current
level until it shuts off. Choosing a current-limit switch allows you to select a
smaller DC/DC converter and inductor because the switch more accurately limits
the current during an overcurrent event. The current-limit switch also allows
for decreased Vdroop in the 5V Vbus during transients versus a fuse
implementation.

ESD protection

When designing USB ports, you should be aware of the high risk for ESD
strikes and consider using ESD protection to prevent damage. For example, USB
controllers and transceivers often handle ESD ratings based on the human body
model. This rating is the oldest and most commonly used to detect ESD
sensitivity. The HBM rating is intended for chip-level ESD protection and does
not guarantee that the system will be protected from higher level ESD strikes.
The International Electrotechnical Commission (IEC) 61000-4-2 standard tests for
higher levels of ESD energy when compared to the HBM rating, as shown in Figure
1. For system-level protection, consider selecting the more robust IEC 61000-4-2
standard and using a transient voltage suppressor (TVS) diode.

In USB 2.0 applications, system-level ESD protection should be considered for
VBUS and the data lines. VBUS requires a large capacitor
for handling power transients like hot-plugging, and therefore can pass IEC
61000-4-2 by means of the capacitor. However, the data lines require a different
approach. The high-speed lines operate at a maximum data rate of 480 Mbps, which
means a large capacitor cannot be added to protect from ESD. You will need a
low-capacitance TVS diode in order to decrease the effect on signal
integrity.

Figure 1: ESD test comparison

Complete solution

Traditionally, multiple devices met the protection requirements for a USB
host: a current-limited load switch for Vbus plus one or more ESD protection
devices for the data pins. The TPD3S014 combines a current-limit switch and two channels of
ESD protection to make a single-chip USB host-port solution as shown in Figure
2. The TPD3S014 and TPD3S044 allow 0.5A and 1.5A of continuous current,
respectively, in a space-saving 2.9 mm by 2.8 mm DBV package.

The current limits in this family feature reverse-current blocking and are
Underwriters’ Laboratories (UL)-recognized components (UL2367). They also
provide IEC 61000-4-2 (Level 4) ESD protection for the data pins. These devices
simplify your designs by reducing the number of devices and shrinking the
overall footprint of the printed circuit board (PCB) to ensure optimal USB
host-port protection.

Figure 2: USB host-port protection
solution

Additional resources:

For more information on port protection, see http://www.ti.com/lsds/ti/interface/esd-emi-protection-overview.page?DCMP=awire&HQS=hval-hvl-ipd-awire-20150325-lp-esd-emi-protection-en.

To explore TI’s comprehensive solutions for ESD, check out our ESD Protection Guide.

To evaluate the TPD3S014, check out the TPD3S014EVM.

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