Datasheet
AD5330/AD5331/AD5340/AD5341
Rev. A | Page 20 of 28
SUGGESTED DATABUS FORMATS
In most applications, GAIN and BUF are hard-wired. However,
if more flexibility is required, they can be included in a databus.
This enables the user to software program GAIN, giving the
option of doubling the resolution in the lower half of the DAC
range. In a bused system, GAIN and BUF can be treated as data
inputs because they are written to the device during a write
operation and take effect when
LDAC
is taken low. This means
that the reference buffers and the output amplifier gain of
multiple DAC devices can be controlled using common GAIN
and BUF lines.
In the case of the AD5330, this means that the databus must be
wider than eight bits. The AD5331 and AD5340 databuses must
be at least 10 bits and 12 bits wide, respectively, and are best
suited to a 16-bit databus system.
Examples of data formats for putting GAIN and BUF on a
16-bit databus are shown in Figure 40. Note that any unused bits
above the actual DAC data can be used for BUF and GAIN. DAC
devices can be controlled using common GAIN and BUF lines.
AD5331
DB
0
DB
1
DB
2
DB
3
DB
4
DB
5
DB
6
DB
7
GAIN XXXX
X
XBUF
AD5330
AD5340
X = UNUSED BIT
DB
0
DB
1
DB
2
DB
3
DB
4
DB
5
DB
6
DB
7
GAIN XXXXBUF DB
9
DB
8
XX DB
0
DB
1
DB
2
DB
3
DB
4
DB
5
DB
6
DB
7
GAINBUF DB
9
DB
8
DB
10
DB
11
06852-041
Figure 40. GAIN and BUF Data on a 16-Bit Bus
The AD5341 is a 12-bit device that uses byte load, so only four
bits of the high byte are actually used as data. Two of the unused
bits can be used for GAIN and BUF data by connecting them to
the GAIN and BUF inputs; for example, Bit 6 and Bit 7, as
shown in Figure 41 and Figure 42.
DATA
INPUTS
BUF
GAIN
LDAC
CLR
CS
WR
HBEN
AD5341
DB
7
DB
6
8-BIT
DATA BUS
0
6852-042
Figure 41. AD5341 Data Format for Byte Load with GAIN and BUF Data
on 8-Bit Bus
In this case, the low byte is written to first in a write operation
with HBEN = 0. Bit 6 and Bit 7 of DAC data are written into
GAIN and BUF registers but have no effect. The high byte is
then written to. Only the lower four bits of data are written into
the DAC high byte register, so Bit 6 and Bit 7 can be GAIN and
BUF data.
LDAC
is used to update the DAC, GAIN, and BUF values.
DB
8
DB
9
HIGH BYTE
LOW BYTE
X = UNUSED BIT
DB
0
DB
1
DB
2
DB
3
DB
4
DB
5
DB
6
DB
7
XX DB
10
DB
11
BUF GAIN
06852-043
Figure 42. AD5341 with GAIN and BUF Data on 8-Bit Bus