MCP4901T-E/P MICROCHIP [Microchip Technology], MCP4901T-E/P Datasheet - Page 33

• Manufacturer Part Number: MCP4901T-E/P
• Description: 8/10/12-Bit Voltage Output Digital-to-Analog Converter with SPI Interface
• Manufacturer: MICROCHIP [Microchip Technology]

6.8
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
is, the less power is dissipated across it. 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 the resolution around the range of interest.
EXAMPLE 6-6:
 2010 Microchip Technology Inc.
(b) Dual Output DAC:
(a) Single Output DAC:
I
I
where
V OUT
b
L
=
=
Building Programmable Current
Source
I
----
-------------- -
R

V
L
sense
OUT

=
shows an example for building a
V
Common-Emitter Current Gain
REF

----------- -


+

G
1
DIGITALLY-CONTROLLED CURRENT SOURCE.
MCP4902
MCP4912
MCP4922

MCP4901
MCP4911
MCP4921
D
------
2
N
n
Example 6-2
V
REF
SPI
would
sense
3-wire
V
D
DAC
N = DAC Bit Resolution
G = Gain select (1x or 2x)
DD
n
= Digital value of DAC (0-255) for MCP4901/MCP4902
= Digital value of DAC (0-1023) for MCP4911/MCP4912
= Digital value of DAC (0-4095) for MCP4921/MCP4922
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.
MCP4901/4911/4921
V
OUT
V
V
CC
CC
–
+
R
SENSE
I
b
V
DD
Load
or V
DS22248A-page 33
I
L
REF