AD5228

Rev. A | Page 13 of 20

Potentiometer Mode Operation

If all three terminals are used, the operation is called potenti-

ometer mode. The most common configuration is the voltage

divider operation as shown in Figure 36.

A

W

B

Figure 36. Potentiometer Mode Configuration

maximum or minimum scale has not been reached during

operation. If the effect of wiper resistance is ignored, the

transfer functions can be simplified as

A

WB

V

PU

V

32

+

=

Δ

(5)

A

WB

V

PD

V

32

+

=

Δ

(6)

Unlike in rheostat mode operation where the absolute tolerance

is high, potentiometer mode operation yields an almost ratio-

metric function of PU/32 or PD/32 with a relatively small error

coefficients, the ratiometric adjustment also reduces the overall

temperature coefficient effect to 5 ppm/°C except at low value

Potentiometer mode operations include an op amp input and

feedback resistors network and other voltage scaling applications.

The A, W, and B terminals can be input or output terminals and

CONTROLLING INPUTS

All PU and PD inputs are protected with a Zener ESD structure

as shown in

.

Figure 37

PU

100k

Ω

DECODE

AND

DEBOUNCE

CKT

Figure 37. Equivalent ESD Protection in PU and PD Pins

PU and PD pins are usually connected to pushbutton tactile

switches for manual operation, but the AD5228 can also be

controlled digitally. It is recommended to add external

MOSFETs or transistors that simplify the logic controls.

UP/DOWN

CONTROL

LOGIC

DISCRETE

STEP/AUTO

SCAN DETECT

ADAPTIVE

DEBOUNCER

ZERO- OR MID-

SCALE PRESET

AD5228

R1

R2

D

E

C

O

D

E

A

W

B

PRE

GND

PU

PD

DOWN

N2

2N7002

UP

N1

2N7002

Figure 38. Digital Control with External MOSFETs

TERMINAL VOLTAGE OPERATION RANGE

The AD5228 is designed with internal ESD diodes for

protection. These diodes also set the voltage boundary of the

terminal operating voltages. Positive signals present on

forward-biased diode. There is no polarity constraint between

than GND.

GND

A

W

B