ADR293

Rev. D | Page 11 of 12

APPLICATIONS

KELVIN CONNECTIONS

In many portable instrumentation applications where PC board

cost and area go hand-in-hand, circuit interconnects are very often

of dimensionally minimum width. These narrow lines can cause

large voltage drops if the voltage reference is required to provide

load currents to various functions. In fact, a circuit’s interconnects

can exhibit a typical line resistance of 0.45 mΩ/square (1 oz. Cu,

for example). Force and sense connections, also referred to as

Kelvin connections, offer a convenient method of eliminating

the effects of voltage drops in circuit wires. Load currents flowing

the load. However, the Kelvin connection in Figure 23 overcomes

the problem by including the wiring resistance within the forcing

loop of the op amp. Because the op amp senses the load voltage,

op amp loop control forces the output to compensate for the

wiring error and to produce the correct voltage at the load.

A1

1µF

100kΩ

SENSE

FORCE

GND

ADR293

2

6

4

Figure 23. Advantage of Kelvin Connection

VOLTAGE REGULATOR FOR PORTABLE

EQUIPMENT

The ADR293 is ideal for providing a stable, low cost, and low

power reference voltage in portable equipment power supplies.

Figure 24 shows how the ADR293 can be used in a voltage

regulator that not only has low output noise (as compared to

switch mode design) and low power, but also a very fast

recovery after current surges. Some precautions should be taken

in the selection of the output capacitors. Too high an ESR

(effective series resistance) could endanger the stability of the

circuit. A solid tantalum capacitor, 16 V or higher, and an

aluminum electrolytic capacitor, 10 V or higher, are recom-

mended for C1 and C2, respectively. In addition, the path from

the ground side of C1 and C2 to the ground side of R1 should

be kept as short as possible.

ADR293

GND

0.1µF

LEAD-ACID

BATTERY

+

6V

CHARGER

INPUT

R1

402kΩ

1%

C1

68µF

TANT

C2

1000µF

ELECT

R2

402kΩ

1%

+

+

5V, 100mA

IRF9530

R3

510kΩ

OP20

2

6

2

7

6

4

3

4

Figure 24. Voltage Regulator for Portable Equipment