Rev Date: 7/29/2022

12

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Please confirm technical specifications before you order and/or use.

CSS / CSSH Series

Ultra-precision Metal Alloy Current Sensing Chip Resistor

Stackpole Electronics, Inc.

Resistive Product Solutions

High Power Chip Resistors and Thermal Management

Stackpole has developed several surface mount resistor series in addition to our current sense resistors, which have had higher power

ratings than standard resistor chips. This has caused some uncertainty and even confusion by users as to how to reliably use these

resistors at the higher power ratings in their designs.

The data sheets for the RHC, RMCP, RNCP, CSR, CSRN, CSRF, CSS, and CSSH state that the rated power assumes an ambient

temperature of no more than 100°C for the CSS / CSSH series and 70°C for all other high power resistor series. In addition, IPC and

UL best practices dictate that the combined temperature on any resistor due to power dissipated and ambient air shall be no more than

105°C

. At first glance this wouldn’t seem too difficult, however the graph below shows typical heat rise for the CSR1206 100 milliohm

at full rated power. The heat rise for the RMCP and RNCP would be similar. The RHC with its unique materials, design, and processes

would have less heat rise and therefore would be easier to implement for any given customer.

The 102°C heat rise shown here would indicate there will be additional thermal reduction techniques needed to keep this part under

105°C total hot spot temperature if this part is to be used at 0.75 watts of power. However, this same part at the usual power rating for

this size would have a heat rise of around 72°C. This additional heat rise may be dealt with using wider conductor traces, larger solder

pads and land patterns under the solder mask, heavier copper in the conductors, via through PCB, air movement, and heat sinks,

among many other techniques. Because of the variety of methods customers can use to lower the effective heat rise of the circuit,

resistor manufacturers simply specify power ratings with the limitations on ambient air temperature and total hot spot temperatures and

leave the details of how to best accomplish this to the design engineers. Design guidelines for products in various market segments

can vary widely so it would be unnecessarily constraining for a resistor manufacturer to recommend the use of any of these methods

over another.

Note:

The final resistance value can be affected by the board layout and assembly process, especially the size of the mounting pads and the amount

of solder used. This is especially notable for

resistance values ≤ 50 mΩ.

This should be taken into account when designing.

RoHS Compliance

Stackpole Electronics has joined the worldwide effort to reduce the amount of lead in electronic components and to meet the various

regulatory

requirements now prevalent, such as the European Union’s directive regarding “Restrictions on Hazardous Substances”

(RoHS 3). As part of this ongoing program, we periodically update this document with the status regarding the availability of our

compliant components. All our standard part numbers are compliant to EU Directive 2011/65/EU of the European Parliament as

amended by Directive (EU) 2015/863/EU as regards the list of restricted substances.