Rainbow Electronics MAX5484 - Manual (Page 13)

MAX5481–MAX5484
10-Bit, Nonvolatile, Linear-Taper Digital
Potentiometers
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where D is the decimal equivalent of the 10 data bits writ-
ten (0 to 1023), V
HL is the voltage difference between the
H and L terminals:
The MAX5481 includes a total end-to-end resistance
value of 10k
Ω while the MAX5482 features an end-to-
end resistance value of 50k Ω. These devices are not
intended to be used as a variable resistor. Wiper cur-
rent creates a nonlinear voltage drop in series with the
wiper. To ensure temperature drift remains within speci-
fications, do not pull current through the voltage-divider
wiper. Connect the wiper to a high-impedance node.
Figures 1 and 2 show the behavior of the MAX5481’s
resistance from W to H and from W to L. This does not
apply to the variable-resistor devices
MAX5483/MAX5484 Variable Resistors
The MAX5483/MAX5484 provide a programmable
resistance between W and L. The MAX5483 features a
total end-to-end resistance value of 10k
Ω, while the
MAX5484 provides an end-to-end resistance value of
50k
Ω. The programmable resolution of this resistance is
equal to the nominal end-to-end resistance divided by
1024 (10-bit resolution). For example, each nominal
segment resistance is 9.8
Ω and 48.8Ω for the MAX5483
and the MAX5484, respectively.
The 10-bit data in the 10-bit latch register selects a
wiper position from the 1024 possible positions, result-
ing in 1024 values for the resistance from W to L.
Calculate the resistance from W to L (R
WL ) by using the
following formula:
where D is decimal equivalent of the 10 data bits writ-
ten, R
W-L is the nominal end-to-end resistance, and R Z
is the zero-scale error. Table 1 shows the values of R WL
at selected codes for the MAX5483/MAX5484.
Digital Interface
Configure the MAX5481–MAX5484 by a pin-selectable,
3-wire, SPI-compatible serial data interface or an
up/down interface. Drive SPI/UD high to select the 3-
wire SPI-compatible interface. Pull SPI/UD low to select
the up/down interface.
R D
D
R R
WL W L Z
( ) = × +
−
1023
V FSE
V
and
V ZSE
V
FSE
HL
ZSE
HL
=
⎡
⎣⎢ ⎤
⎦⎥
=
⎡
⎣⎢ ⎤
⎦⎥
1024
1024
,
MAX5483
(10k Ω DEVICE)
MAX5484
(50k Ω DEVICE)
CODE
(DECIMAL)
R WL ( Ω) R WL ( Ω)
0 70 110
1 80 160
512 5070 25,110
1023 10,070 50,110
Table 1. R
WL
at Selected Codes
CODE (DECIMAL)
R
W-H
(k
Ω
)
896 768 512 640 256 384 128
2
4
6
8
10
12
14
16
18
0
0 1024
50k Ω DEVICE SCALES BY A FACTOR OF FIVE
Figure 1. Resistance from W to H vs. Code (10k Ω Voltage-Divider)
CODE (DECIMAL)
R
W-L
(k
Ω
)
896 768 512 640 256 384 128
2
4
6
8
10
12
14
16
18
0
0 1024
50k Ω DEVICE SCALES BY A FACTOR OF FIVE
Figure 2. Resistance from W to L vs. Code (10k Ω Voltage-Divider)