Hardware Reference
In-Depth Information
The functions of the MCP4922 signals are as follows:
AV
SS
: analog ground.
CS
: chip select. This signal enables/disables inputs.
SDI
: serial data input.
LDAC
: latch DAC input. When this signal is low, the input latch registers' contents are
transferred to the
DA
C registers. This signal can be tied low if data transfer on the
risin
g edge of the CS signal is desired.
SHDN
: Shut down input. When this signal is low, the MCP4922 is in the low-power
standby mode.
DACx outputs (
V
OUTA
,
V
OUTB
)
:
V
OUTA
and
V
OUTB
are DAC outputs. The DAC output amplifiers
drive these pins with a range of AV
SS
to V
DD
.
SCK
: serial clock input. The MCP4922 can shift data with the SCK frequency up to
20 MHz.
V
DD
: positive power supply.
The microprocessor or microcontroller sends in a 16-bit frame that consists of 4 bits of
command and 12 bits of data to the MCP4922 to start a D/A conversion. The contents of the
16-bit data frame are shown in Figure 10.18. The control bit SHDN allows the user to shut
down the MCP4922 to save power when it is not needed.
15
14
13
12
11
10
9
8
7
6
5
4
3
2
1
0
A/B
BUF
D11
D10
D9
D8
D7
D6
D5
D4
D3
D2
D1
D0
GA
SHDN
A/B: DAC
A
or DAC
B
select
0 = write to DAC
A
.
1 = write to DAC
B
.
BUF: V
REF
input buffer control
0 = unbuffered.
1 = buffered.
GA: output gain select bit
0 = gain is 2 (V
OUT
= 2
D/4096).
1 = gain is 1 (V
OUT
= V
REF
×
D/4096).
×
V
REF
×
SHDN: output power down control bit
0 = output buffer is disabled. Output is in high impedance.
1 = output buffer is enabled.
D11:D0: DAC data bits
Figure 10.18
■
Input data format for the MCP4922 DAC
The output voltage of the MCP4922 is given by the following expression:
V
OUT
5
GA
×
V
REF
×
code
÷
2
12
Where,
GA
is the selected gain (can be 1 or 2). Code is the value (represented by D11, . . . , D0)
to be converted to voltage.
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