參數資料
型號: MCP4441-503E/ML
廠商: Microchip Technology
文件頁數: 75/100頁
文件大?。?/td> 0K
描述: IC DGTL POT 129TAPS QUAD 20QFN
標準包裝: 91
接片: 129
電阻(歐姆): 50k
電路數: 4
溫度系數: 標準值 150 ppm/°C
存儲器類型: 非易失
接口: I²C(設備位址)
電源電壓: 2.7 V ~ 5.5 V
工作溫度: -40°C ~ 125°C
安裝類型: 表面貼裝
封裝/外殼: 20-VFQFN 裸露焊盤
供應商設備封裝: 20-QFN 裸露焊盤(4x4)
包裝: 管件
MCP444X/446X
DS22265A-page 76
2010 Microchip Technology Inc.
8.5
Implementing Log Steps with a
Linear Digital Potentiometer
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 shows a block diagram of one of the
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 VDD/VSS
voltage limits.
FIGURE 8-7:
Signal Attenuation Block
Diagram - Ground Referenced.
Equation 8-1 shows the equation to calculate voltage
dB gain ratios for the digital potentiometer, while
Equation 8-2 shows the equation to calculate
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
(RB2GND) must be included into the calculation.
Equation 8-3 shows this equation.
EQUATION 8-1:
dB CALCULATIONS
(VOLTAGE)
EQUATION 8-2:
dB CALCULATIONS
(RESISTANCE) - CASE 1
EQUATION 8-3:
dB CALCULATIONS
(RESISTANCE) - CASE 2
Table 8-1 shows the codes that can be used for 8-bit
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 red text. At lower
wiper code values, the attenuation may skip a step, if
this occurs the next attenuation value is colored
magenta to highlight that a skip occurred. For example,
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).
P0A
MCP44X1
P0W
P0B
L = 20 * log10 (VOUT / VIN)
dB
VOUT / VIN Ratio
-3
0.70795
-2
-1
0.79433
0.89125
L = 20 * log10 (RBW / RAB)
Terminal B connected to Ground (see Figure 8-7)
L = 20 * log10 ( (RBW + RB2GND) / (RAB + RB2GND) )
Terminal B through RB2GND to Ground
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