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Logically isolated current sense resistor pad

IP.com Disclosure Number: IPCOM000030313D
Original Publication Date: 2004-Aug-05
Included in the Prior Art Database: 2004-Aug-05
Document File: 1 page(s) / 43K

Publishing Venue

IBM

Abstract

Method of logical separation of kelvin terminals for a standard package current sense resistor. This allows a standard two-terminal resistor package to show up as a four-terminal part for separate autorouting of the sense line and current carrying lines without major modifications to the software design package.

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Logically isolated current sense resistor pad

Background for this idea comes from Peripheral Component Interconnect-X (PCI-X) hotplug circuit but applies anywhere a surface mount technology (SMT) current sense resistor is used. Currently in logics, a current sense resistor (CSR) is represented as a two-terminal device with four connections. One pair of connections is the power feed to the protected device that the CSR is connected in-line with. The second set of connections is the differential sense lines back to the controller chip. Unfortunately, this arrangement results in the differential sense nets having the same logical name as the supply lines (due to the fact they hook to the same pins on the resistor). This results in problems when the cards go to be wired. Because the nets are the same logical name to the card designer or auto-router, they appear to be the same net and all the normal rules apply. This can and does result in mis-wired sense pairs (or properly wired sense lines with an extra via connecting the sense line to the power supply plane where it was not expected) that will introduce parasitic resistance into the circuit (most sense resistors are in the 0.01 Ohm range) and cause it to trip too soon. Currently, all CSR circuits must be inspected by hand and any mis-connections corrected by hand.

     The solution is a four-terminal resistor with a special pad to allow two different logical nets connect to one physical pad without generating errors in...