With the popularization of Industry 4.0, Industrial Internet of Things and 5G telephony technology, more and more complex electronic equipment are deployed in harsher and more difficult to enter environments.

Original: Jeff Shepard@DigiKey Electronics

With the popularity of Industry 4.0, Industrial Internet of Things (IIoT) and G telephony technology, more and more complex electronic equipment are deployed in harsher and more difficult to enter environments. This enables repeatable, deterministic protection against electrostatic discharge (ESD) and electrical overstress (EOS) events in applications such as industrial robots, IO-Link interfaces, industrial sensors and IIoT devices, programmable logic controllers (PLC) and Power over Ethernet (PoE). These applications need to meet the transient protection requirements of the IEC61000 standard. While Transient Voltage Suppression (TVS) diodes serve designer requirements well, an increasing number of applications require more deterministic, linear, compact and reliable ESD and EOS protection.

To meet these increasing performance and form factor requirements, transient shunt suppressor (TDS) devices can be used. This device combines excellent clamping, linearity and temperature stability for more assured performance levels. TDS devices do not dissipate surge energy like TVS diodes do, but transfer this energy to ground. Compared to TVS alternatives, TDS does not dissipate energy, so its size can be smaller, which helps reduce solution size. In addition, the clamping voltage of TDS devices is 30% lower than that of TVS diodes, thus reducing the electrical stress on the system and improving reliability.

This article explains how TDS devices work and the benefits they bring to critical applications. Then, the TDS devices of Semtech are introduced as examples and PCB layout guidelines for successfully applying these devices are given.

How TDS surge protectors work

Surge stage field effect transistors (FET) are the main protective components in TDS devices. When an EOS event occurs and the transient voltage exceeds the breakdown voltage (VBR) of the integrated precision flip-flop circuit, the drive circuit is activated, and the field effect transistor is turned on to conduct the transient energy (IPP) to the ground (Figure 1).

Image source: Semtech

Figure 1: In a TDS device, when an EOS event is detected, a precision flip-flop circuit (left) activates the FET voltage-controlled switch (right), transferring the energy spike (IPP) directly to ground

As the pulse current increases to IPP, the FET's on-resistance (RDS(ON)) becomes a few milliohms (mΩ), the clamp voltage (VC) is almost the same as the trigger circuit's VBR. Therefore, the VC of a TDS device is almost constant over the IPP range. This is different from the clamping effect in a TVS device, which is known as:

where Rdyn is the dynamic resistor.

In TVS devices, the Rdyn value is fixed so that the clamping voltage increases linearly with the increase of IPP within the range of rated current . For TDS devices, VC is stable over the operating temperature as well as the IPP range, achieving decisive EOS protection (Figure 2).

Image source: Semtech

Figure 2: For TDS devices such as TDS2211P (solid line), the clamping voltage remains constant over temperature and Ipp, thus providing deterministic EOS protection. The VC of the

TDS device is relatively low, so the protected device is not only subject to lower electrical stress, but also improves reliability (Figure 3).

Image source: Semtech

Figure 3: The low VC of TDS devices (represented here by VClamp, green curve) improves reliability by reducing the electrical stress on the protected device. The performance of the

TDS device supports system designs that meet the requirements of multiple standards: ESD immunity requirements of IEC 61000-4-2, burst/electrical fast transient (EFT) immunity requirements of IEC 61000-4-4, and surge immunity requirements of IEC 61000-4-5. This makes TDS devices suitable for many harsh environment applications. Examples of TDS applications are described below, including 22V TDS devices used to protect load switches, 33V TDS devices suitable for protecting IO-Link transceivers, and 58 V TDS devices that can be used to protect PoE devices.

Protecting Load Switches

Use the 22 V TDS2211P to protect load switches, electronic fuse inputs in industrial equipment, robots, remote instrumentation, USB Power Delivery (PD) and IIoT devices from EOS events. The EOS protection levels of the TDS device include:

• The ESD withstand voltage level of contact and air is ±30kV, which complies with the requirements of the IEC61000-4-2 standard.
• The rated current of the peak pulse is 40A (tp = 8/20μs), which complies with the IEC 61000-4-5 standard requirements; ±1kV (tp = 1.2/50μs, shunt resistance (RS) = 42Ω), in line with IEC 61000-4-5 standard requirements, suitable for asymmetric lines
• EFT withstand voltage of ±4 kV (100kHz and 5kHz, 5/50ns), in line with IEC 61000-4-4 Standard

When used in this configuration, the TDS2211P protects downstream devices from lightning strikes, ESD, and other EOS events. The device also maintains VC below the damage threshold of the switching FET in the load switch (Figure 4).

Image source: Semtech

Figure 4: The TDS2211P can be used to protect the load switch (HS2950P) and downstream devices from lightning, ESD, and other EOS events.

I0-Link Protection

In addition to the common ESD and EOS hazards that occur in industrial environments, you may encounter voltage spikes of thousands of volts when plugging I0-Link transceivers into or unplugging from I0-Link master devices. TVS diodes typically used to protect I0-Link transceivers can be supplemented with TDS devices to improve protection performance. In a typical circuit protection application, the device used is rated for at least 115% of the input supply, so for 24V applications like I0-Link, a 33V protection device like TDS3311P TDS is appropriate. The main specifications of TDS3311P are as follows:

• The ESD withstand voltage of contact and air is ±30kV, which meets the requirements of the IEC61000-4-2 standard.
• The peak pulse current capability is 35A (tp = 8/20 μs), and 1kV (tp = 1.2/50μs, RS = 42Ω) , Meet the asymmetric line requirements of the IEC61000-4-5 standard
• Meet the burst/EFT immunity requirements of the IEC61000-4-4 standard

There are two common I0-Link port configurations, 3-pin and 4-pin. These two configurations require slightly different protection schemes. In both cases, the TDS device can be supplemented with a µClamp3671P TVS diode on the VBUS (L+ (24V)) line to provide reverse polarity protection (Figure 5).

Image source: Semtech

Figure 5: Comparison of ESD protection for a 3-pin I0-Link port (top) and a 4-pin I0-Link port (bottom) using TDS devices (green rectangle).

In the 3-pin case, 3 TDS devices are required. If required, bidirectional protection can be provided by two TDS3311Ps facing each other. In the 4-pin case, all four pins of the I0-Link port should withstand both positive and negative surges. Testing is required between each pair of pins in the connector to ensure the surge protection performance of the I0-Link transceiver and should be tested to the required levels of IEC 61000-4-2 ESD, IEC 61000-4-4 Burst/EFT and IEC 61000-4-5 surge.

PoE protection

PoE protection scheme must take into account that EOS events may be common mode (relative to ground) or differential (line to line). The supply voltage of PoE is 48V, so a 58V TDS device like TDS5801P can be used to provide EOS protection on the RJ-45 connector side.The specifications of TDS5801P are as follows:

• ESD withstand voltage: ±15kV (contact) and ±20kV (air), in line with the requirements of the IEC61000-4-2 standard
• Peak pulse current capability: 20A (tp = 8/20 μs), 1kV (tp = 1.2/50μs, RS = 42Ω) , In line with the requirements of the IEC61000-4-5 standard
• According to the requirements of IEC61000-4-4, the EFT withstand voltage is ±4kV (100kHz and 5kHz, 5/50ns)

Power in a PoE system is provided through the center tap connection of the transformer. The PD (RJ-45) side must protect both Mode A (power supplied via data pairs 1 and 2, data pairs 3 and 6) and Mode B (power supplied via pins 4 and 5 and pins 7 and 8), so two pairs of TDS5801P are required to achieve bidirectional protection across the center-tap connection (Figure 6).

Image source: Semtech

Figure 6: Back-to-back TDS devices (green, TDS5801P) provide bidirectional protection in PoE systems against EOS events. The

transformer provides common mode isolation but does not provide differential surge protection. During a differential EOS event, the transformer winding on the line side is charged and the energy is transferred to the secondary side until the surge ends or the transformer becomes saturated. The TDS devices on the PD side can be supplemented with four RClamp3361P ESD protection devices located on the Ethernet physical layer (PHY) side of the transformer to protect against differential EOS events.

TDS device

SurgeSwitch TDS device provides designers with a variety of operating voltage options, including 22 V (TDS2211P), 30V (TDS3011P), 33V (TDS3311P), 40V (TDS4001P), 45V (TDS4501P) and 58V (TDS5801P) (Table 1). These devices meet the requirements of the IEC61000 standard for use in systems operating in harsh 5G telephony and industrial environments.

Table 1: SurgeSwitch devices are rated from 22V to 58V to meet many application requirements. (Image source: Semtech)

Because TDS devices are non-dissipative devices and transfer surge energy directly to ground through a low impedance path, they can be packaged in a small package of 1.6 x 1.6 x 0.55mm, which can significantly save board space compared to the SMA and SMB packages commonly used by other surge protection devices. The 6-pin DFN package includes 3 input pins and 3 pins for transferring surge energy to ground (Figure 7).

Image source: Semtech

Figure 7: The TDS device comes in a 1.6 x 1.6 x 0.55mm DFN package with 6 leads (right); pins 1, 2, and 3 are connected to ground, while pins 4, 5, and 6 are used as EOS/ESD protection inputs.

Board Layout Guidelines

When mounting a SurgeSwitch TDS device on a circuit board, all of its ground pins (1, 2, and 3) must be connected to the same trace, and all of its input pins (4, 5, and 6) must also be connected to the same trace for maximum surge current capability. If the ground trace is on a different layer of the board, it is highly recommended to use multiple vias to connect to the ground plane (Figure 8). Follow these PC board layout guidelines to minimize parasitic inductance and optimize device performance. Additionally, SurgeSwitch TDS devices should be placed as close as possible to the protected connector or device. This minimizes instantaneous energy coupling to the trace, which is especially important during fast rise time EOS events. Since the TDS device does not dissipate any energy, there is no need to set thermal pad under the device to conduct heat energy.

Figure 8: When the ground planes are on different layers of the circuit board, for best performance it is recommended to use multiple vias for the connection. (Image source: Semtech)

Summary of this article

For designers of industrial and 5G phone equipment that operate in harsh environments, TDS devices can be used to provide reliable, deterministic protection from ESD and EOS events.The VC of TDS devices is relatively low, which improves system reliability by reducing electrical stress on components. These devices meet the transient protection requirements of the IEC61000 standard and are available in a 22V to 58V voltage range to meet the requirements of specific applications. The small size of TDS devices helps reduce the overall solution size, but designers need to follow some simple PC board layout requirements to maximize the performance of TDS devices.

Finally, if you like this article, share it with more friends! Remember to give it a like!