MCP41XXX/42XXX
4.0
APPLICATIONS INFORMATION
power-up, all data registers will automatically be loaded
with the mid-scale value (80h). The serial interface pro-
vides the means for loading data into the shift register,
which is then transferred to the data registers. The
serial interface also provides the means to place indi-
vidual potentiometers in the shutdown mode for maxi-
mum power savings. The SHDN pin can also be used
to put all potentiometers in shutdown mode and the RS
pin is provided to set all potentiometers to mid-scale
(80h).
The MCP41XXX/42XXX devices are 256 position
single and dual digital potentiometers that can be used
in place of standard mechanical pots. Resistance val-
ues of 10 kΩ, 50 kΩ and 100 kΩ are available. As
shown in Figure 4-1, each potentiometer is made up of
a variable resistor and an 8-bit (256 position) data reg-
ister that determines the wiper position. There is a
nominal wiper resistance of 52Ω for the 10 kΩ version,
125Ω for the 50 kΩ and 100 kΩ versions. For the dual
devices, the channel-to-channel matching variation is
less than 1%. The resistance between the wiper and
either of the resistor endpoints varies linearly according
to the value stored in the data register. Code 00h
effectively connects the wiper to the B terminal. At
PA0
PW0
PB0 PA1
PW1
PB1
RDAC1
Data Register 0
D7
RS
D0
RDAC2
Data Register 1
D7
D0
Decode
Logic
CS
D7
D0
16-bit Shift Register
SCK
SI
SO
SHDN
FIGURE 4-1:
Block diagram showing the MCP42XXX dual digital potentiometer. Data register 0 and
data register 1 are 8-bit registers allowing 256 positions for each wiper. Standard SPI pins are used with
the addition of the Shutdown (SHDN) and Reset (RS) pins. As shown, reset affects the data register and
wipers, bringing them to mid-scale. Shutdown disconnects the A terminal and connects the wiper to B,
without changing the state of the data registers.
V
DD
0.1 uF
V
DD
0.1 uF
B
W
A
To Application
Circuit
When laying out the circuit for your digital potentiome-
ter, bypass capacitors should be used. These capaci-
tors should be placed as close as possible to the device
pin. A bypass capacitor value of 0.1 µF is recom-
mended. Digital and analog traces should be separated
as much as possible on the board, with no traces run-
ning underneath the device or the bypass capacitor.
Extra precautions should be taken to keep traces with
high-frequency signals (such as clock lines) as far as
possible from analog traces. Use of an analog ground
plane is recommended in order to keep the ground
potential the same for all devices on the board.
µC
Data Lines
2003 Microchip Technology Inc.
MCP4XXXX
DS11195C-page 13
MICROCHIP [ MICROCHIP TECHNOLOGY ]
