MCP4726A2T-E Datasheet, PDF (68/86 Pages) Microchip Technology – 8-/10-/12-Bit Voltage Output Digital-to-Analog Converter

MCP4706/4716/4726
8.6 Designing a Double-Precision
DAC
Figure 8-7 shows an example design of a single-supply
voltage output capable of up to 24-bit resolution. This
requires two 12-bit DACs. This design is simply a
voltage divider with a buffered output.
As an example, if a similar application to the one
developed in Section 8.5.1 “Bipolar DAC Example
Using MCP4726” required a resolution of 1 µV instead
of 1 mV, and a range of 0V to 4.1V, then 12-bit
resolution would not be adequate.
Step 1: Calculate the resolution needed:
4.1V/1 µV = 4.1 x 10⁶. Since 2²² = 4.2 x 10⁶,
22-bit resolution is desired. Since
DNL = ±0.75 LSb, this design can be attempted
with the 12-bit DAC.
Step 2: Since DAC_B’s V_OUTB has a resolution of 1 mV,
its output only needs to be “pulled” 1/1000 to meet
the 1 µV target. Dividing V_OUTA by 1000 would
allow the application to compensate for DAC_B’s
DNL error.
Step 3: If R₂ is 100Ω, then R₁ needs to be 100 kΩ.
Step 4: The resulting transfer function is shown in the
equation of Example 8-6.
Optional
V_REF V_DD
V_OA
MCP4726 (A)
I²C™
R₁
2-wire
Optional
V_REF V_DD
0.1 µF
V_CC+
V_OUT
R₂
MCP4726 (B)
V_OB
I²C™
2-wire
V_CC–
FIGURE 8-7:
Simple Double Precision
DAC using MCP4726.
EQUATION 8-6: V_OUT CALCULATION
V_OUT =
V_{OA *} R₂ + V_{OB *} R₁
R₁ + R₂
Where:
V_OA = (V_REF * G * DAC A Register Value)/4096
V_OB = (V_REF * G * DAC B Register Value)/4096
G = Selected Op Amp Gain
8.7 Building Programmable Current
Source
Figure 8-8 shows an example of building a
programmable current source using a voltage follower.
The current sensor resistor is used to convert the DAC
voltage output into a digitally-selectable current source.
The smaller R_SENSE is, the less power dissipated
across it. However, this also reduces the resolution that
the current can be controlled.
Optional
V_REF V_DD
MCP47X6
V_CC+
V_OUT
V_DD
(or V_REF)
Load
I_L
I²C™
2-wire
I_b
V_CC–
I_b = ^I-_β--^L-
R_SENSE
I_L = _R-V---s-^O--_e--^Un---_s-^T-_e × _β-----+-^β-----1-
where β = Common-Emitter Current Gain.
FIGURE 8-8:
Source.
Digitally-Controlled Current
DS22272C-page 68
© 2011-2012 Microchip Technology Inc.