AS1502 datasheet(10/14 Pages) AMSCO

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AS1500

Data Sheet - Deta iled Description

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:

RWA (Dx)= (256 - Dx)/256 • RAB + RW

(EQ 2)

where RAB is the nominal resistance between terminal A and B, RW is the wiper resistance and Dx is the 8-Bit Code

word. In Table 8 the resistor values between the wiper and terminal B for AS1500 are given for specific codes Dx.

Figure 6. 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

VW (Dx)= (Dx)/256 • VAB + VB

(EQ 3)

where VAB is the voltage applied between terminal A and B, VW is the voltage at the wiper, Dx is the 8-Bit Code word

and VB is the voltage at terminal B. The temperature drift is 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.

Table 8. RDAC-Codes WA

DX (Dec)

RWA (Ω)

Output State

255

Full Scale

128

5050

Midscale

10011

1 LSB

10050

Zero-Scale

Rs=RNOMINAL/256

RDAC

LATCH

AND

DECODE

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