ADR430 datasheet(17/24 Pages) AD

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ADR430/ADR431/ADR433/ADR434/ADR435/ADR439

Rev. B | Page 17 of 24

+VDD

–

VREF

GND

VIN

VOUT

ADR43x

–

VDD

A1 = OP777, OP193

Figure 33. Negative Reference

HIGH VOLTAGE FLOATING CURRENT SOURCE

The circuit in Figure 34 can be used to generate a floating

current source with minimal self-heating. This particular

configuration can operate on high supply voltages determined

by the breakdown voltage of the N-channel JFET.

VIN

VOUT

GND

OP90

+VS

SST111

VISHAY

2N3904

2.1k

Ω

–VS

ADR43x

Figure 34. High Voltage Floating Current Source

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 through wiring resistance produce

an error (VERROR = R × IL) at the load. However, the Kelvin

connection of Figure 35 overcomes the problem by including

the wiring resistance within the forcing loop of the op amp.

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

control forces the output to compensate for the wiring error and

to produce the correct voltage at the load.

VIN

VOUT

GND

RLW

VOUT

SENSE

VOUT

FORCE

RLW

VIN

ADR43x

A1 = OP191

Figure 35. Advantage of Kelvin Connection

DUAL POLARITY REFERENCES

Dual polarity references can easily be made with an op amp and

a pair of resistors. In order not to defeat the accuracy obtained

by ADR43x, it is imperative to match the resistance tolerance as

well as the temperature coefficient of all the components.

–

10V

VIN

VOUT

GND

TRIM

V+

V–

+10V

–5V

+5V

10k

Ω

µF

0.1

µF

ADR435

OP1177

Ω

10k

Ω

Figure 36. +5 V and −5 V References Using ADR435

VIN

VOUT

GND

TRIM

5.6k

Ω

V+

V–

+10V

ADR435

OP1177

+2.5V

–2.5V

5.6k

Ω

–10V

Figure 37. +2.5 V and −2.5 V References Using ADR435

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