10.2.1.2.1.1 Application Curve

Figure 10-2. REF7025 Startup (C = 10 μF)

10.2.1.2.2 Force and Sense Connection

Current flowing through a PCB trace produces an IR voltage drop, and with longer traces, this drop can reach

several millivolts or more, introducing a considerable error into the output voltage of the reference. A 3000-mil

long, 15-mil wide trace of 1-ounce copper has a resistance of approximately 100 mΩ at room temperature; at a

load current of 10 mA, this can introduce a full millivolt of error. In an ideal board layout, the reference must be

mounted as close as possible to the load to minimize the length of the output traces, and, therefore, the error

introduced by voltage drop. However, in applications where this is not possible or convenient, force and sense

connections (sometimes referred to as Kelvin sensing connections) are provided as a means of minimizing the

IR drop and improving accuracy.

Kelvin connections work by providing a set of high impedance voltage-sensing lines to the output and ground

nodes. Because very little current flows through these connections, the IR drop across their traces is negligible,

and the output and ground. The REF70 has kelvin connection capabilities due to its output force (OUTF) and

input sense (OUTS) connection as shown in Basic Reference Connection. The output force voltage will vary

its architecture, therefore if the load current is expected to be less than 4mA, then OUTF should be shorted to

OUTS.

It is always advantageous to use Kelvin connections whenever possible. However, in applications where the IR

simply be tied together close to the pins, and the device can be used in the same fashion as a normal 3-terminal

reference.

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REF70

SNAS781C – OCTOBER 2020 – REVISED SEPTEMBER 2021

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