ADR293

REV. 0

–10–

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 mW/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 of Figure 22 overcomes

the problem by including the wiring resistance within the forcing

loop of the op amp. Since 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.

ADR293

4

6

2

GND

100k

1 F

SENSE

FORCE

Figure 22. 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 23 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 elec-

trolytic capacitor, 10 V or higher, are recommended for C1 and

C2, respectively. Also, the path from the ground side of C1 and

C2 to the ground side of R1 should be kept as short as possible.

2

3

6

7

2

4

4

GND

ADR293

R1

402k

1%

R2

402k

1%

OP-20

++

C1

68 F

TANT

C2

1000 F

ELECT

+5V, 100mA

IRF9530

R3

510k

CHARGER

INPUT

+

LEAD-ACID

BATTERY

6V

0.1 F

Figure 23. Voltage Regulator for Portable Equipment