MCP4921-E/P Microchip Technology Inc., MCP4921-E/P Datasheet - Page 21

• Manufacturer Part Number: MCP4921-E/P
• Description: SINGLE 12-BIT DAC WITH SPI INTERACE
• Manufacturer: Microchip Technology Inc.

Specifications of MCP4921-E/P

• Lead Free Status / Rohs Status: RoHS Compliant part Electrostatic Device

6.4
The MCP492X is a rail-to-rail (R-R) input and output
DAC designed to operate with a V
5.5V. Its output amplifier is robust enough to drive com-
mon, small-signal loads directly, thus eliminating the
cost and size of an external buffer for most applications.
6.4.1
A common application for a DAC with the MCP492X’s
performance is digitally-controlled set points and/or
calibration of variable parameters, such as sensor off-
set or slope. 12-bit resolution provides 4096 output
steps. If a 4.096V V
represent 1 mV of resolution. If a smaller output step
size is desired, the output range would need to be
reduced.
EXAMPLE 6-1:
 2004 Microchip Technology Inc.
SPI™
Single-Supply Operation
DC SET POINT OR CALIBRATION
V
REF
3
MCP492X
V
DD
REF
Set Point or Threshold Calibration.
is provided, an LSB would
V
V
OUT
trip
V
OUT
DD
=
=
V
V
range of 2.7V to
REF
OUT
R
G


1
------------------
R
-------
2
D
12
1
R
+
2
R
R
2
2


R
sense
V
DD
6.4.1.1
If the output range is reduced relative to AV
reducing V
put step. If the application is calibrating the threshold
of a diode, transistor or resistor tied to AV
a theshold range of 0.8V may be desired to provide
200 µV resolution. Two common methods to achieve a
0.8V range is to either reduce V
voltage divider on the DAC’s output. If a V
able with the desired output value, using that V
option. Occasionally, when using a low-voltage V
the noise floor causes SNR error that is intolerable.
The voltage divider method provides some advantages
when V
output voltage is not available. In this case, a larger
value V
range down to the precise desired level. Using a com-
mon V
Example 6-1 illustrates this concept. Note that the volt-
age divider can be connected to AV
depending on the application’s requirements.
The MCP492X’s low, ±0.75 (max.) DNL performance
is critical to meeting calibration accuracy in production.
REF
0.1 uF
REF
REF
output has availability and cost advantages.
REF
G = Gain select (1x or 2x)
D = Digital value of DAC (0 – 4096)
is used while two resistors scale the output
needs to be very low or when the desired
V
Decreasing The Output Step Size
trip
will reduce the magnitude of each out-
MCP4921/4922
Comparator
V
V
CC
CC
+
–
REF
DS21897A-page 21
to 0.82V or use a
SS
REF
SS
SS
or V
REF
or V
, simply
is avail-
is an
REF
REF
REF
,
,
,