18

REF3425

SBAS804 – SEPTEMBER 2017

www.ti.com

Product Folder Links: REF3425

Submit Documentation Feedback

Copyright © 2017, Texas Instruments Incorporated

Best performance and stability is attained with low-ESR, low-inductance ceramic chip-type output capacitors

(X5R, X7R, or similar). If using an electrolytic capacitor on the output, place a 0.1-μF ceramic capacitor in parallel

to reduce overall ESR on the output.

9.2.2.2 4-Wire Kelvin Connections

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 1-inch long,

5-millimeter 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

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

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

reference (as shown in Figure 25).

In applications with slow-rising input voltage signals, the reference exhibits overshoot or other transient

anomalies that appear on the output. These phenomena also appear during shutdown as the internal circuitry

loses power.

To avoid such conditions, ensure that the input voltage wave-form has both a rising and falling slew rate close to

6 V/ms.

9.2.2.4 Shutdown/Enable Feature

The REF3425 references can be switched to a low power shut-down mode when a voltage of 0.5 V or lower is

input to the ENABLE pin. Likewise, the reference becomes operational for ENABLE voltages of 1.6 V or higher.

During shutdown, the supply current drops to less than 2 μA, useful in applications that are sensitive to power

consumption.

If using the shutdown feature, ensure that the ENABLE pin voltage does not fall between 0.5 V and 1.6 V

because this causes a large increase in the supply current of the device and may keep the reference from

starting up correctly. If not using the shutdown feature, however, the ENABLE pin can simply be tied to the IN

pin, and the reference remains operational continuously.