Data Sheet AS1500/1/2/3

Revision 1.0, Oct 2004

Page 6 of 8

Ω

Ω

Ω

Ω)

Output State

255

10061

Full Scale

128

5100

Midscale

1

139

1 LSB

0

100

Zero-Scale

(Wiper Contact Resistance)

Table 7: RDAC-Codes WB

The maximum current through the wiper and terminal B is

5mA. If the current exceeds this limit the internal switches

can degrade or even be damaged. As a mechanical

symmetrical. The relation between them is shown in Figure

4.

The resistance RWA is the complimentary resistor to RWB

and can be controlled digitally as well. RWA starts at the

maximum value of the nominal resistance and is reduced

with increasing 8-Bit code words. The formula to calculate

RWA is given below:

word. In Table 8 the resistor values between the wiper and

Ω

Ω

Ω

Ω)

Output State

255

89

Full Scale

128

5050

Midscale

1

10011

1 LSB

0

10050

Zero-Scale

Table 8: RDAC-Codes WA

Figure 5: Equivalent RDAC Circuit

Voltage Output Operation

The AS150x family can easily used in an voltage output

mode, where the output voltage is proportional to an

applied voltage to a given terminal. When 5V are applied to

terminal A and B is set to ground the ouput voltage at the

wiper starts at zero volts up to 1LSB less then 5V. One

LSB of voltage corresponds to the voltage applied at

terminal AB divided through 256 steps of possible wiper

settings. The formula is given by

significant better than in Rheostat mode, since the

temperature coefficient is determined by the internal

resistor ratio. Therefore the temperature drift is only

15ppm/°C.

Applications

The digital potentiometer can replace in many applications

the

analog

trimming

potentiometer.

The

digital

potentiometer is not sensitive to vibrations and shocks. It

has an extremely small form-factor and can be adjusted

very fast (e.g. AS1500 has an update rate of 600kHz)

Furthermore the temperature drift, resolution and noise are

significant better and cannot be achieved with a

mechanical

trimming

potentiometer.

Due

to

the

programmability the resistor settings can be stored in the

system memory, so that after a power down the exact

settings can be recalled easily.

All analog signals must remain within 0 to VDD range. For

standard potentiometer applications the wiper output can

be used directly. In the case of a low impedance load a

buffer shall be used.

CODE -

0

25

50

75

10

0

64

121925

RDAC

LATCH

AND

DECODE

A

W

B

D7

D6

D5

D4

D3

D2

D1

D0