Datasheet

MCP4901/4911/4921
DS22248A-page 34  2010 Microchip Technology Inc.
6.9 Using Multiplier Mode
The MCP4901/4911/4921 and MCP4902/MCP4912/
MCP4922 family devices use external reference, and
these devices are ideally suited for use as a multiplier/
divider in a signal chain. Common applications are: (a)
precision programmable gain/attenuator amplifiers and
(b) motor control feedback loops. The wide input range
(0V – V
DD
) is in Unbuffered mode, and near rail-to-rail
range in Buffered mode. Its bandwidth (> 400 kHz),
selectable 1x/2x gain and low power consumption give
maximum flexibility to meet the application’s needs.
To configure the device for multiplier applications,
connect the input signal to V
REF
and serially configure
the DAC’s input buffer, gain and output value. The
DAC’s output can utilize any of the examples from 6-1
to 6-6, depending on the application requirements.
Example 6-7 is an illustration of how the DAC can
operate in a motor control feedback loop.
If the gain selection bit is configured for 1x mode
(<GA
>=1), the resulting input signal will be attenuated
by D/2
n
. With the 12-bit DAC (MCP4921 or MCP4922),
if the gain is configured for 2x mode (<GA
>=0), codes
less than 2048 attenuate the signal, while codes
greater than 2048 gain the signal.
A DAC provides significantly more gain/attenuation
resolution when compared to typical programmable
gain amplifiers. Adding an op amp to buffer the output,
as illustrated in Examples 6-2 through 6-6, extends the
output range and power to meet the precise needs of
the application.
EXAMPLE 6-7: MULTIPLIER MODE USING V
REF
INPUT.
V
CC
+
V
CC
–
V
REF
DAC
V
RPM
+
–
V
DD
SPI
3
V
OUT
R
sense
V
RPM_SET
Z
FB
MCP4901
MCP4911
MCP4921
(a) Single Output DAC:
(b) Dual Output DAC:
MCP4902
MCP4912
MCP4922
V
OUT
V
REF
G
D
n
2
N
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