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ELECTRONICS

Overcurrent protection
Many surge stoppers have the ability to monitor current and
protect against overcurrent events. This is achieved by monitoring
the voltage drop across a series sense resistor and responding
appropriately. Inrush current can also be monitored and controlled
to protect the MOSFET. The response can be similar to an
overvoltage condition, as it either disconnects by latching off or
riding through the event if the circuitry can handle the power levels.

Reverse input protection
Reverse input protection is possible due to the wide operating
capabilities of the surge stopper devices (capable of withstanding
up to 60 V below ground potential on some devices). Figure 10
shows a back-to-back MOSFET implementation of reverse current Figure 11: LTC4366 high voltage floating topology
protection. During normal operation, Q2 and Q1 are turned on by
the GATE pin, and Q3 doesn’t have any impact. However, when the most appropriate device. Follow these few steps to narrow the
a reverse voltage condition exists, Q3 turns on, pulling Q2’s gate field: 1. Go to ADI’s protection family parametric table. 2. Choose
down to the negative input and isolating Q1, protecting the output. input voltage range. 3. Choose the number of channels. 4. Filter
Reverse output voltage protection is also achieved with robust on features to narrow the possible options.
device pin protection, with up to 20 V below ground potential
possible, depending on the device selected. As with all product selection, it is important to understand your
system requirements before looking for the correct device. Some
important considerations are the expected supply voltage and
the voltage tolerance of downstream electronics (important for
deciding the clamp voltage), as well as any particular features that
are important for the design.

Some example-filtered parametric tables are shown below for
reference. These can further be modified on the website to
include some other parameters.
• The high voltage surge stopper devices can be found here.
• Protection controllers with the OV disconnect feature can be
found here.

Conclusion
Regardless of the surge stopper type implemented, active, IC-
based surge stopper designs eliminate the need for bulky TVS
diodes or large profile inductors and capacitors for filtering. This
results in an overall smaller area and a lower profile solution. The
output voltage clamp is more accurate than a TVS with 1% to
Figure 10: LT4363 reverse input protection circuit. 2% accuracy possible. This prevents overdesign and allows for
downstream devices with tighter tolerances to be selected.
For applications that require wide input voltage ranges, a floating The system protection family of devices available from Analog
topology surge stopper can be used. When a surge event occurs, Devices enables designers to implement reliable, flexible and
the full surge voltage is seen by the surge stopper IC so the small form factor protection for downstream devices—especially
internal transistor technology limits the voltage range of the IC. those facing harsh overvoltage and overcurrent events, which
With a floating surge stopper such as the LTC4366, the IC floats can occur in many industrial, automotive, aerospace, and
just below the output voltage, giving it a much wider operating communications-based designs. n
voltage range. A resistor is placed in the return line (VSS), which
allows the IC to float up with the supply voltage. The result is an References
input voltage limitation set by the voltage capability of the external - “AN-9768: Transient Suppression Devices and Principles.”
components and MOSFETs. Figure 11 shows an application - Littelfuse, January 1998.
“Fuseology.” Automotive Passenger Car Solutions Catalog,
circuit capable of operating from a very high dc supply while Littelfuse, 2014.
protecting the downstream load. - Kalb, Jim. “Total Clearing Time” Technical Bulletin, OptiFuse,
January 2010.
- Megaw, David. “Protecting and Powering Automotive Electronics
Choosing the right device for my application Systems with No Switching Noise and 99.9% Efficiency.” Analog
In many ways, because of their inherently robust design, using Dialogue, Vol. 54, No. 1, February 2020.
a surge stopper simplifies protection circuit design. Data sheets - Wu, Bin and Zhongming Ye. “Comprehensive Power Supply
System Designs for Harsh Automotive Environments Consume
can help greatly with sizing components, with many possible Minimal Space, Preserve Battery Charge, Feature Low EMI.”
applications already shown. The hardest part might be choosing Analog Dialogue, Vol. 53, No. 3, August 2019.

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