Datasheet

MCP40D17/18/19
DS22152B-page 42 © 2009 Microchip Technology Inc.
Step resistance (R
S
) is the resistance from one tap
setting to the next. This value will be dependent on the
R
AB
value that has been selected. Equation 6-1 shows
the calculation for the step resistance while Table 6-2
shows the typical step resistances for each device.
EQUATION 6-1: R
S
CALCULATION
Equation 6-2 illustrates the calculation used to
determine the resistance between the wiper and
terminal B.
EQUATION 6-2: R
WB
CALCULATION
The digital potentiometer is available in four nominal
resistances (R
AB
) where the nominal resistance is
defined as the resistance between terminal A and
terminal B. The four nominal resistances are 5 kΩ,
10 kΩ, 50 kΩ, and 100 kΩ.
The total resistance of the device has minimal variation
due to operating voltage (see Figure 2-11, Figure 2-29,
Figure 2-47, or Figure 2-65).
TABLE 6-2: STEP RESISTANCES
A POR/BOR event will load the Volatile Wiper register
value with the default value. Table 6-3 shows the
default values offered.
TABLE 6-3: DEFAULT FACTORY
SETTINGS SELECTION
Part Number
Resistance (Ω)
Case
Total
(R
AB
)
Step (R
S
)
MCP40D17/18/19-
502
Minimum 4000 31.496
Typical 5000 39.370
Maximum 6000 47.244
MCP40D17/18/19-
103
Minimum 8000 62.992
Typical 10000 78.740
Maximum 12000 94.488
MCP40D17/18/19-
503
Minimum 40000 314.961
Typical 50000 393.701
Maximum 60000 472.441
MCP40D17/18/19-
104
Minimum 80000 629.921
Typical 100000 787.402
Maximum 120000 944.882
R
S
R
AB
127
---------=
R
WB
R
AB
N
127
--------------R
W
+=
N = 0 to 127 (decimal)
Resistance
Code
Typical
R
AB
Value
Default POR Wiper
Setting Code
(1)
-502 5.0 kΩ Mid-scale 3Fh
-103 10.0 kΩ Mid-scale 3Fh
-503 50.0 kΩ Mid-scale 3Fh
-104 100.0 kΩ Mid-scale 3Fh
Note 1: Custom POR/BOR Wiper Setting options
are available, contact the local Microchip
Sales Office for additional information.
Custom options have minimum volume
requirements.