Product Introduction Videos

Welcome to a brief technical presentation from SSM USA on current sensing low resistance chip resistors.

This presentation will provide an overview of Susumu’s current sensing low resistance chip resistors,
including their application, characteristics and a simple explanation of the technology behind them.

Current sensing low resistance chip resistors, introduced originally as an over-current protection device in
power source circuits, have expanded their application range and have become indispensable components
for power management of mobile devices and for high frequency circuits. They are also used to adjust
current to control motor speed and solenoids.

Current sensing low resistance chip resistors require several key characteristics such as tight tolerance,
low TCR, current surge tolerance and low thermal emf. However, in this technical presentation, we will
focus on two of the most important features of Susumu’s current sensing low resistance chip resistors,
their power handling capability and their low noise characteristics for high speed application.

This chart illustrates the relationship between standard chip size and power handling capabilities. The red
dots show typical size for each rated power. Susumu’s RL, PRL, and RP series low resistance chips are
consistently at least one size smaller than others.
In fact, the new PRL1632 is the world’s smallest 1W low resistance chip resistor.

This shows the actual comparison of the temperature for the 1W rated low resistance chip resistors.
Susumu’s PRL shows an even temperature distribution slightly exceeding 100degree ℃, while our
competitor’s part shows a significant hot spot exceeding 200degree ℃ in the middle of the resistor.
This is why Susumu can offer higher wattage low resistance chip resistors in smaller sizes.

The technology is simple. If you have one resistive element in the middle, that is where the hot spot
appears. Instead of a central resistive element, our parts have a heat dissipative copper electrode in the
center and our resistive elements are placed at the edges of the ceramic substrate, resulting in an even
distribution of the heat generated by the resistive elements.

In high frequency applications, noise control is a serious issue. The components’ innate inductance, such
as equivalent series inductance, is the major source for the noise. Inductance can be minimized by
widening and shortening the resistive element. Susumu offers two configurations of low resistance chip
resistors, short side electrode and long side electrode as shown in the picture. The long side electrode
style has inherently less noise due to its wider and shorter resistive element.

This is the actual ESL measurement data for our own low resistance chip resistors. As shown in the figure,
the long side terminal low resistance chip resistors clearly have less inductance than our short side chip
counterparts.

In an actual DC DC converter switching circuit at several hundred kHz, the use of a short-side terminal
resistor results in a transient switching pulse wave with a noise peak at each onset of the wave as shown
in the picture on the left. The noise disappears when using a long side terminal current sensing chip
resistor as shown in the picture on the right. Using such low ESL current sensing resistors, the designer
can avoid employing additional noise reduction circuits.

In Summary, In addition to the regular requirements of tight tolerance, low TCR, surge current tolerance and low thermal
emf, Sususmu’s current sensing low resistance chip resistors boast the smallest size for the required
power and significantly low noise due to their small equivalent series inductance. Susumu offers a variety
of low resistance chip resistors for any application such as over current protection, high frequency power
management, and motor speed control. Susumu’s components are all RoHS compliant. Thank you for
listening to this presentation.