MCP47DA1 Datasheet, PDF (54/76 Pages) Microchip Technology – 6-Bit Windowed Volatile DAC with Command Code

MCP47DA1
8.3 Building Programmable Current
Source
Figure 8-6 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 is dissipated
across it. However, this also reduces the resolution that
the current can be controlled.
V_REF V_DD
MCP47DA1
V_CC+
V_OUT
V_DD
(or V_REF)
Load
I_L
I²C™
2-wire
I_b
V_CC–
I_b = ^I-_--^L-
I_L = _R-V---s-^O--_e--^Un---_s-^T-_e  _-----+-^-----1-
R_SENSE
where Common-Emitter Current Gain
FIGURE 8-6:
Source.
Digitally-Controlled Current
8.4 Serial Interface Communication
Times
Table 8-1 shows the time for each I²C Serial Interface
command as well as the effective data update rate that
can be supported by the digital interface (based on the
two I²C serial interface frequencies). The continuous
Write command allows a higher data update frequency,
since for the fixed overhead, more bytes are
transferred. So, the serial interface performance along
with the V_OUT output performance (such as slew rate),
is used to determine the application’s volatile DAC
register update rate.
TABLE 8-1: SERIAL INTERFACE TIMES / FREQUENCIES
Example
Command
Time (µs)
Effective Data Update
Frequency (kHz) ⁽²⁾
Command
# of Serial # Bytes # of Serial
Interface bits⁽¹⁾ Transferred Interface bits 100 kHz 400 kHz 100 kHz 400 kHz
Write Single byte
29
1
29
290.0
72.5
3.4
13.8
Write Continuous bytes 20 + N * 9
5
65
650.0 162.5
7.7
30.8
Read byte
39
1
39
390.0
97.5
2.6
10.3
Note 1: Includes the Start or Stop bits.
2: This is the command frequency multiplied by the number of bytes transferred.
DS25118D-page 54
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