MCP4801 Datasheet, PDF (29/48 Pages) Microchip Technology – 8/10/12-Bit Voltage Output Digital-to-Analog Converter with Internal VREF and SPI Interface

MCP4801/4811/4821
6.7 Selectable Gain and Offset Bipolar
Voltage Output
In some applications, precision digital control of the
output range is desirable. Example 6-4 illustrates how
to use the MCP4801/4811/4821 family of 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.
EXAMPLE 6-4:
BIPOLAR VOLTAGE SOURCE WITH SELECTABLE GAIN AND OFFSET
R₂
V_DD
V_CC+
V_OUTA
R₁
DAC_A
(DAC_A for Gain Adjust)
V_CC+
V_DD
V_O
DAC_B
V_OUTB
R₅
R₃
V_IN+
SPI
3
(DAC_B for Offset Adjust)
R_{4 0.1 µF}
V_CC–
V_OUTA
=
2.048

G_A

D-----_n-
2^N
V_CC–
V_OUTB = 2.048  G_B  ^D-2---_N-ⁿ-
V_IN+
=
-V---^O----^U----^T---^B---R----⁴----+-----V----^C---^C----^--R----³-
R₃ + R₄
G = Gain selection (1x or 2x)
N = DAC bit resolution
D_n = Digital value of DAC (0-255) for MCP4801
= Digital value of DAC (0-1023) for MCP4811
= Digital value of DAC (0-4095) for MCP4821
V_O
=
V_{IN+}1 + ^RR----21-_
–
V_O
UT
A


RR----_{21-}
Offset Adjust Gain Adjust
Thevenin
Equivalent
Bipolar “Window” DAC using R₄ and R₅
V₄₅
=
-V---^C----^C---⁺---R----⁴----+-----V----^C---^C----^---R---⁵-
R₄ + R₅
R₄₅
=
----R----⁴---R---⁵----
R₄ + R₅
V_IN+
=
V----_{O----U----T---B---R----4--5----+------V----4--5---R----3}
R₃ + R₄₅
V_O
=
V_{IN+}1 + ^RR----21-_
–
V
OU

TA_
RR----_{21-}
Offset Adjust Gain Adjust
 2010 Microchip Technology Inc.
DS22244B-page 29