ADR430/ADR431/ADR433/ADR434/ADR435/ADR439

Rev. J | Page 19 of 24

GND

SENSE

FORCE

2

6

4

ADR43x

A1

OP191

+

Figure 37. Advantage of Kelvin Connection

DUAL POLARITY REFERENCES

Dual polarity references can easily be made with an operational

amplifier and a pair of resistors. To avoid defeating the accuracy

obtained by the ADR43x, it is imperative to match the resistance

tolerance as well as the temperature coefficient of all the components.

6

2

4

5

–

10V

GND

TRIM

R1

R2

U2

R3

V+

V–

+10V

–5V

+5V

10kΩ

1µF

0.1µF

U1

ADR435

OP1177

5kΩ

10kΩ

Figure 38. +5 V and −5 V References Using ADR435

6

2

4

5

GND

TRIM

R1

5.6kΩ

U2

V+

V–

+10V

U1

ADR435

OP1177

+2.5V

–2.5V

R2

5.6kΩ

–10V

Figure 39. +2.5 V and −2.5 V References Using ADR435

PROGRAMMABLE CURRENT SOURCE

Together with a digital potentiometer and a Howland current

pump, the ADR435 forms the reference source for a programmable

current as

W

B

B

A

L

V

R

R1

R

R2

I

×

⎟

⎟

⎟

⎟

⎠

⎞

⎜

⎜

⎜

⎜

⎝

⎛

+

=

2

2

(4)

and

REF

N

W

V

D

V

×

=

2

(5)

where:

D is the decimal equivalent of the input code.

N is the number of bits.

achieve the necessary current within the A2 output current

driving capability. In this example, the OP2177 can deliver a

maximum output current of 10 mA. Because the current pump

employs both positive and negative feedback, C1 and C2

capacitors are needed to ensure that the negative feedback

prevails and, therefore, avoids oscillation. This circuit also

the digital potentiometer are supplied with the dual polarity

references, as shown in Figure 40.

6

2

4

5

GND

TRIM

C2

10pF

U1

V+

V–

ADR435

OP2177

R1

50kΩ

OP2177

V–

V+

A2

A1

U2

AD5232

W

A

B

R1'

50kΩ

R2'

1kΩ

1kΩ

10Ω

C1

10pF

+

VL

–

Figure 40. Programmable Current Source