MCP41050-ISN Datasheet, PDF (16/32 Pages) Microchip Technology – Single/Dual Digital Potentiometer with SPI™ Interface

MCP41XXX/42XXX
1/2
MCP42010
V_B
A
B
(SIG -)
V_A
(SIG +)
V_DD
+
-IN
MCP601
A
+IN _-
V_SS
B
V_OUT
V_REF
Where:
V_OUT
=
(V_A
–
V_B)
-^R----^B--
R_A
R_A
=
R_{-----A----B---}(_--2_----5_---6_-----–_----D_-----n---)
256
R_B
=
R_{-----A----B---}D_-----n-
256
R_AB = Total Resistance of pot
D_n = Wiper setting forD_n = 0 to 255
NOTE: Potentiometer values must be equal
FIGURE 4-7:
Single Supply
programmable differential amplifier using digital
potentiometers.
4.2.3 PROGRAMMABLE OFFSET TRIM
For applications requiring only a programmable voltage
reference, the circuit in Figure 4-8 can be used. This
circuit shows the device used in the potentiometer
mode along with two resistors and a buffered output.
This creates a circuit with a linear relationship between
voltage-out and programmed code. Resistors R₁ and
R₂ can be used to increase or decrease the output volt-
age step size. The potentiometer in this mode is stable
over temperature. The operation of this circuit over
temperature is shown in Figure 2-3. The worst perfor-
mance over temperature will occur at the lower codes
due to the dominating wiper resistance. R₁ and R₂ can
also be used to affect the boundary voltages, thereby
eliminating the use of these lower codes.
V_DD
R₁
A
B
V_DD
-
-IN
MCP606
+IN ₊
OUT
V_SS
0.1 uF
R₂
V_SS
FIGURE 4-8:
By changing the values of
R₁ and R₂, the voltage output resolution of this
programmable voltage reference circuit is
affected.
DS11195C-page 16
4.3 Calculating Resistances
When programming the digital potentiometer settings,
the following equations can be used to calculate the
resistances. Programming code 00h effectively brings
the wiper to the B terminal, leaving only the wiper resis-
tance. Programming higher codes will bring the wiper
closer to the A terminal of the potentiometer. The equa-
tions in Figure 4-9 can be used to calculate the terminal
resistances. Figure 4-10 shows an example calculation
using a 10 kΩ potentiometer.
PA
PW
PB
R_WA(D_n)
=
(_---R_{----A----B---})_---(_--2_----5_---6_-----–_----D_-----n---)
256
+
R_W
R_WB(D_n)
=
(_---R_{----A----B---})_---(_--D_-----n---)
256
+
R_W
Where:
PA is the A terminal
PB is the B terminal
PW is the wiper terminal
R_WA is resistance between Terminal A and wiper
R_WB is resistance between Terminal B and Wiper
R_AB is overall resistance for pot (10 kΩ, 50 kΩ or 100 kΩ)
R_W is wiper resistance
D_n is 8-bit value in data register for pot number n
FIGURE 4-9:
Potentiometer resistances
are a function of code. It should be noted that,
when using these equations for most feedback
amplifier circuits (see Figure 4-4 and Figure 4-5),
the wiper resistance can be omitted due to the
high impedance input of the amplifier.
10 kΩ
PA
Example:
R = 10 kΩ
PW
Code = C0h = 192d
PB
R_WA(D_n)
=
(_---R_{----A----B---})_---(_--2_----5_---6_-----–_----D_-----n---)
256
+
R_W
R_WA(C0h)
=
(_---1_---0_----k_---Ω_-----)_---(_--2_---5_----6_-----–_----1_---9_----2_----) _{+ 52Ω}
256
R_WA(C0h) = 2552Ω
R_WB(D_n)
=
(_---R_{----A----B----})_--(_--D_-----n---)
256
+
R_W
R_WB(C0h)
=
(_---1_---0_----k_---Ω_-----)_---(_--1_----9_---2_----)
256
+
52Ω
R_WB(C0h) = 7552Ω
Note: All values shown are typical and
actual results will vary.
FIGURE 4-10:
Example Resistance
calculations.
 2003 Microchip Technology Inc.