MCP4801T-E/P MICROCHIP [Microchip Technology], MCP4801T-E/P Datasheet - Page 31

• Manufacturer Part Number: MCP4801T-E/P
• Description: 8/10/12-Bit Voltage Output Digital-to-Analog Converter with Internal VREF and SPI Interface
• Manufacturer: MICROCHIP [Microchip Technology]

6.9
Example 6-6
programmable current source using a voltage follower.
The current sensor (sensor resistor) is used to convert
the DAC voltage output into a digitally-selectable
current source.
Adding the resistor network from
be advantageous in this application. The smaller
R
EXAMPLE 6-6:
 2010 Microchip Technology Inc.
SENSE
I
where
I
L
b
=
=
-------------- -
R
V
Building Programmable Current
Source
is, the less power dissipated across it.
I
----

(a) Single Output DAC:
(b) Dual Output DAC:

L
sense
OUT
Common-Emitter Current Gain
shows an example of building a

------------ -

+

1
DIGITALLY-CONTROLLED CURRENT SOURCE
MCP4801
MCP4811
MCP4821
MCP4802
MCP4812
MCP4822
Example 6-2
SPI
would
3-wire
V
DAC
DD
D
G
N
n
=
=
=
=
=
Gain selection (1x or 2x)
Digital value of DAC (0-255) for MCP4801/MCP4802
Digital value of DAC (0-1023) for MCP4811/MCP4812
Digital value of DAC (0-4095) for MCP4821/MCP4822
DAC bit resolution
However, this also reduces the resolution that the
current can be controlled with. The voltage divider, or
“window”, DAC configuration would allow the range to
be reduced, thus increasing resolution around the
range of interest. When working with very small sensor
voltages, plan on eliminating the amplifier’s offset error
by storing the DAC’s setting under known sensor
conditions.
V
OUT
MCP4801/4811/4821
V
V
CC
CC
–
+
R
I
SENSE
b
V
DD
Load
or V
REF
I
L
DS22244B-page 31