MCP4431 Microchip Technology Inc., MCP4431 Datasheet - Page 68

• Manufacturer Part Number: MCP4431
• Description: 7/8-bit Volatile Quad Digital Pot With I 2c Interface
• Manufacturer: Microchip Technology Inc.

MCP443X/5X
8.5
In audio volume control applications, the use of
logarithmic steps is desirable since the human ear
hears in a logarithmic manner. The use of a linear
potentiometer can approximate a log potentiometer,
but with fewer steps. An 8-bit potentiometer can
achieve fourteen 3 dB log steps plus a 100% (0 dB)
and a mute setting.
Figure 8-7
MCP44x1 resistor networks being used to attenuate an
input signal. In this case, the attenuation will be ground
referenced. Terminal B can be connected to a common
mode voltage, but the voltages on the A, B and Wiper
terminals must not exceed the MCP44x1’s V
voltage limits.
FIGURE 8-7:
Diagram - Ground Referenced.
Equation 8-1
dB gain ratios for the digital potentiometer, while
Equation 8-2
resistance dB gain ratios. These two equations assume
that the B terminal is connected to ground.
If terminal B is not directly resistively connected to
ground, then this terminal B to ground resistance
(R
Equation 8-3
DS22267A-page 68
B2GND
) must be included into the calculation.
Implementing Log Steps with a
Linear Digital Potentiometer
shows a block diagram of one of the
shows this equation.
shows the equation to calculate voltage
shows
P0A
MCP44X1
Signal Attenuation Block
the
P0B
P0W
equation
to
calculate
DD
/V
SS
EQUATION 8-1:
EQUATION 8-2:
EQUATION 8-3:
Table 8-1
digital potentiometers to implement the log attenuation.
The table shows the wiper codes for -3 dB, -2 dB, and
-1 dB attenuation steps. This table also shows the
calculated attenuation based on the wiper code’s linear
step. Calculated attenuation values less than the
desired attenuation are shown with
wiper code values, the attenuation may skip a step, if
this occurs the next attenuation value is colored
magenta
in the -3 dB column the -48 dB value is highlighted
since the -45 dB step could not be implemented (there
are no wiper codes between 2 and 1).
Terminal B connected to Ground (see
Terminal B through R
L = 20 * log
L = 20 * log
to highlight that a skip occurred. For example,
shows the codes that can be used for 8-bit
10
10
L = 20 * log
dB
-3
-2
-1
(R
( (R
BW
BW
B2GND
/ R
dB CALCULATIONS
(VOLTAGE)
dB CALCULATIONS
(RESISTANCE) - CASE 1
dB CALCULATIONS
(RESISTANCE) - CASE 2
V
+ R
 2010 Microchip Technology Inc.
OUT
AB
10
0.70795
0.79433
0.89125
B2GND
)
(V
to Ground
/ V
OUT
IN
) / (R
Ratio
/ V
red
IN
Figure
AB
)
text. At lower
+ R
B2GND
8-7)
) )