ADR3512

Data Sheet

Rev. E | Page 14 of 16

APPLICATIONS INFORMATION

BASIC VOLTAGE REFERENCE CONNECTION

The circuit shown in Figure 37 shows the basic configuration for

the ADR3512 reference. Connect bypass capacitors according to

the guidelines in the following sections.

2.7V TO

5.5V

1.2V

0.1µF

1µF

0.1µF

8

1

6

7

2

3

ADR3512

ENABLE

GND FORCE

GND SENSE

Figure 37. Basic Reference Connection

INPUT AND OUTPUT CAPACITORS

Connect a 1 µF to 10 µF electrolytic or ceramic capacitor to the

input to improve transient response in applications where the

supply voltage may fluctuate. Connect an additional 0.1 µF ceramic

capacitor in parallel to reduce high frequency supply noise.

Connect a ceramic capacitor of at least a 0.1 µF to the output to

improve stability and help filter out high frequency noise. An

additional 1 µF to 10 µF electrolytic or ceramic capacitor can be

added in parallel to improve transient performance in response

to sudden changes in load current; however, note that doing so

increases the turn-on time of the device.

Best performance and stability is attained with low equivalent

series resistance (ESR) (for example, less than 1 Ω), 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.

4-WIRE KELVIN CONNECTIONS

Current flowing through a printed circuit board (PCB) trace

produces an IR voltage drop. 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 mm 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 is

mounted as close to the load as possible to minimize the length of

the output traces, and, therefore, the error introduced by the

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 voltages

can be sensed accurately.

These voltages are fed back into the internal amplifier and are used

to automatically correct for the voltage drop across the current

carrying output and ground lines, resulting in a highly accurate

output voltage across the load. To achieve the best performance,

connect the sense connections directly to the point in the load

where the output voltage is the most accurate. See Figure 38 for an

example application.

LOAD

0.1µF

0.1µF

1µF

OUTPUT CAPACITOR(S) SHOULD

BE MOUNTED AS CLOSE

CONNECT SENSE

CONNECTIONS AS

CLOSE AS POSSIBLE

TO LOAD DEVICE.

8

1

6

7

2

3

ADR3512

ENABLE

GND FORCE

GND SENSE

Figure 38. Application Showing Kelvin Connection

It is always advantageous to use Kelvin connections whenever

possible. However, in applications where the IR drop is negligible

or an extra set of traces cannot be routed to the load, the

ground can simply be tied together, and the device can be used

in the same way as a normal 3-terminal reference (see Figure 37).

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 waveform

has both a rising and falling slew rate of at least 0.1 V/ms.

SHUTDOWN/ENABLE FEATURE

The ADR3512 reference can be switched to a low power shutdown

mode when a voltage of 0.7 V or lower is input to the ENABLE pin.

Likewise, the reference becomes operational for ENABLE voltages

to less than 5 µA, useful in applications that are sensitive to power

consumption.

If using the shutdown feature, ensure that the ENABLE pin

causes a large increase in the supply current of the device and

may keep the reference from starting up correctly (see Figure 31).

If not using the shutdown feature, however, the ENABLE pin

operational.