Data Sheet

MCP4725
DS22039D-page 36 © 2009 Microchip Technology Inc.
8.5.3 BUILDING A “WINDOW” DAC
Some sensor applications require very high resolution
around the set point or threshold voltage.
Example 8-2 shows an example of creating a “window”
around the threshold using a voltage divider network
with a pull-up and pull-down resistor. In the circuit, the
output voltage range is scaled down, but its step
resolution is increased greatly.
EXAMPLE 8-2: Single-Supply “Window” DAC.
V
TRIP
R
1
R
2
0.1 µF
Comparator
R
3
V
CC-
Where: Dn = DAC Input Code (0 – 4095)
V
CC+
V
CC+
V
CC-
V
OUT
V
OUT
V
DD
Dn
2
12
-------
×=
R
23
R
2
R
3
R
2
R
3
+
-------------------=
V
23
V
CC+
R
2
()V
CC-
R
3
()+
R
2
R
3
+
------------------------------------------------------=
V
trip
V
OUT
R
23
V
23
R
1
+
R
2
R
23
+
---------------------------------------------=
R
1
R
23
V
23
V
OUT
V
O
Thevenin
Equivalent
R
sense
To MCU
(MASTER)
R
R
MCP4725
V
DD
V
OUT
A0
SCL
V
SS
1
2
3
4
5
6
V
DD
SDA
10 µF0.1 µF
V
DD