參數(shù)資料
型號: ADM00317
廠商: Microchip Technology
文件頁數(shù): 64/86頁
文件大?。?/td> 0K
描述: BOARD DAUGHTER MCP4706/16/26
標(biāo)準(zhǔn)包裝: 1
DAC 的數(shù)量: 3 個,每 IC 1 個
位數(shù): 8,10,12
設(shè)置時間: 6µs
DAC 型: 電壓
已供物品: 子板
已用 IC / 零件: MCP4706,MCP4716,MCP4726
2011-2012 Microchip Technology Inc.
DS22272C-page 67
MCP4706/4716/4726
8.5
Selectable Gain and Offset Bipolar
Voltage Output
In some applications, precision digital control of the
output range is desirable. Figure 8-6 illustrates how to
use the DAC devices to achieve this in a bipolar or
single-supply application.
This circuit is typically used for linearizing a sensor
whose slope and offset varies.
The equation to design a bipolar “window” DAC would
be utilized if R3, R4 and R5 are populated.
8.5.1
BIPOLAR DAC EXAMPLE USING
MCP4726
An output step size of 1 mV, with an output range of
±2.05V, is desired for a particular application.
Step 1: Calculate the range: +2.05V – (-2.05V) = 4.1V.
Step 2: Calculate the resolution needed:
4.1V/1 mV = 4100
Since 212 = 4096, 12-bit resolution is desired.
Step 3: The amplifier gain (R2/R1), multiplied by
full-scale VOUT (4.096V), must be equal to the
desired minimum output
to
achieve bipolar
operation. Since any gain can be realized by
choosing resistor values (R1+R2), the VREF value
must be selected first. If a VREF of 4.096V is used,
solve for the amplifier’s gain by setting the DAC to
0, knowing that the output needs to be -2.05V.
The equation can be simplified to:
Step 4: Next, solve for R3 and R4 by setting the DAC to
4096, knowing that the output needs to be +2.05V.
FIGURE 8-6:
Bipolar Voltage Source with
Selectable Gain and Offset.
EQUATION 8-4:
VOUT, VOA+, AND VO
CALCULATIONS
EQUATION 8-5:
BIPOLAR “WINDOW” DAC
USING R4 AND R5
R
2
R
1
---------
2.05
4.096V
-----------------
=
If R1 = 20 kΩ and R2 = 10 kΩ, the gain will be 0.5.
R
2
R
1
------
1
2
---
=
R
4
R
3
R
4
+
()
------------------------
2.05V
0.5 4.096V
()
+
1.5 4.096V
-------------------------------------------------------
2
3
---
==
If R4 = 20 kΩ, then R3 = 10 kΩ
R3
VCC+
VCC
VOUT
I2C
2-wire
VREF
Optional
MCP4726
VDD
R2
VO
VIN
R1
R4
C1
R5
Optional
VOA+
VCC+
VCC
C1 = 0.1 F
Offset Adjust
Gain Adjust
VOUT = VREF G
DAC Register Value
2N
VOA+ =
VOUT R4 + VCC- R5
R3 + R4
VO = VOA+ ( 1 +
) - VIN (
)
R2
R1
R2
R1
Thevenin
Equivalent
V
45
V
CC+R4
V
CC-R5
+
R
4
R
5
+
---------------------------------------------
=
V
IN+
V
OUTR45
V
45R3
+
R
3
R
45
+
---------------------------------------------
=
R
45
R
4R5
R
4
R
5
+
-------------------
=
V
O
V
IN+ 1
R
2
R
1
------
+
V
A
R
2
R
1
------
=
Offset Adjust Gain Adjust
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