Datasheet
V
OUT
+ 2V
REF
code)2
19
2
20
V
OUT
+ 2V
REF
code)2
15
2
16
V
OUT
+ 2V
REF
code
2
20
V
OUT
+ 2V
REF
code
2
16
DAC1220
SBAS082G –FEBRUARY 1998–REVISED SEPTEMBER 2009......................................................................................................................................
www.ti.com
Setting the Output Voltage The code may be given in either straight binary or
offset two's complement format. This is controlled by
To set the DAC1220 output voltage, write a code to
the DF bit in the Command Register (see the register
the Data Input Register (DIR). A write to any of the
description in Table 13 for details). The two data
bytes in the DIR causes the voltage to change at the
format options and the 16- or 20-bit option give rise to
completion of the write command.
four transfer functions, which are shown in Table 8.
For reference, several ideal output voltages for given
The DAC1220 operates in either 16- or 20-bit mode.
input codes are shown in Table 9.
The DIR is 24 bits wide, and the code stored in it is
left justified, with the least significant bits ignored.
Note that the DIR code can also be considered a
Therefore, in 16-bit mode, only the upper 16 bits of
24-bit number. This may be convenient in software. In
the DIR are significant, and in 20-bit mode, only the
this case the transfer functions for 16- and 20-bit
upper 20 bits of the DIR are significant.
modes are the same, except that in 16-bit mode the
code is truncated by eight bits, and in 20-bit mode the
In 20-bit mode, all three bytes of the DIR must be
code is truncated by four bits.
written to in order to completely update the code. In
16-bit mode, it is only necessary to write to the two
upper bytes; a write to the lower byte has no effect on
the output.
Table 8. Transfer Functions
DATA FORMAT 20-BIT MODE 16-BIT MODE
Offset two's complement
Straight binary
Table 9. Example Output Voltages
APPROXIMATE
OUTPUT
VOLTAGE RESOLUTION DATA FORMAT CODE DIR CONTENT
(1)
Two's complement 8000h 8000xxh
16-bit
Straight binary 0000h 0000xxh
0V
Two's complement 8000h 80000xh
20-bit
Straight binary 0000h 00000xh
Two's complement 0000h 0000xxh
16-bit
Straight binary 8000h 8000xxh
2.5V
Two's complement 0000h 00000xh
20-bit
Straight binary 8000h 80000xh
Two's complement 7FFFh 7FFFxxh
16-bit
Straight binary FFFFh FFFFxxh
5V
Two's complement 7FFFFh 7FFFFxh
20-bit
Straight binary FFFFFh FFFFFxh
(1) x = Do not care
14 Submit Documentation Feedback Copyright © 1998–2009, Texas Instruments Incorporated
Product Folder Link(s): DAC1220