AD5363 Analog Devices, AD5363 Datasheet - Page 17

• Manufacturer Part Number: AD5363
• Description: 8-Channel, 14-Bit, Serial Input, Voltage-Output DAC
• Manufacturer: Analog Devices

Specifications of AD5363

• Resolution (bits): 14bit
• Dac Settling Time: 20µs
• Single-supply: No
• Dac Type: Voltage Out
• Dac Input Format: Ser,SPI

A/B REGISTERS AND GAIN/OFFSET ADJUSTMENT
Each DAC channel has seven data registers. The actual DAC
data-word can be written to either the X1A or X1B input
register, depending on the setting of the A /B bit in the control
register. If the A /B bit is 0, data is written to the X1A register.
If the A /B bit is 1, data is written to the X1B register. Note that
this single bit is a global control and affects every DAC channel
in the device. It is not possible to set up the device on a per-
channel basis so that some writes are to X1A registers and some
writes are to X1B registers.
Each DAC channel also has a gain (M) register and an offset (C)
register, which allow trimming out of the gain and offset errors
of the entire signal chain. Data from the X1A register is operated
on by a digital multiplier and adder controlled by the contents of
the M and C registers. The calibrated DAC data is then stored in
the X2A register. Similarly, data from the X1B register is operated
on by the multiplier and adder and stored in the X2B register.
Although a multiplier and an adder symbol are shown in Figure 21
for each channel, there is only one multiplier and one adder in
the device, which are shared among all channels. This has impli-
cations for the update speed when several channels are updated
at once, as described in the Register Update Rates section.
Each time data is written to the X1A register, or to the M or C
register with the A /B control bit set to 0, the X2A data is recal-
culated and the X2A register is automatically updated. Similarly,
X2B is updated each time data is written to X1B, or to M or C
with A /B set to 1. The X2A and X2B registers are not readable
or directly writable by the user.
Data output from the X2A and X2B registers is routed to the
final DAC register by a multiplexer. A 4-bit A/B select register
associated with each group of four DACs controls whether each
individual DAC takes its data from the X2A or X2B register. If a
bit in this register is 0, the DAC takes its data from the X2A
register; if 1, the DAC takes its data from the X2B register.
Note that because there are eight bits in two registers, it is possible
to set up, on a per-channel basis, whether each DAC takes its
data from the X2A or X2B register. A global command is also
provided that sets all bits in the A/B select registers to 0 or to 1.
REGISTER
REGISTER
REGISTER
REGISTER
X1A
X1B
Figure 21. Data Registers Associated with Each DAC Channel
M
C
MUX
REGISTER
REGISTER
X2A
X2B
MUX
REGISTER
DAC
DAC
Rev. A | Page 17 of 28
All DACs in the AD5362/AD5363 can be updated simultane-
ously by taking LDAC low when each DAC register is updated
from either its X2A or X2B register, depending on the setting of
the A/B select registers. The DAC register is not readable or
directly writable by the user. LDAC can be permanently tied
low, and the DAC output is updated whenever new data appears
in the appropriate DAC register.
OFFSET DACS
In addition to the gain and offset trim for each DAC, there are
two 14-bit offset DACs, one for Group 0 and one for Group 1.
These allow the output range of all DACs connected to them to
be offset within a defined range. Thus, subject to the limitations
of headroom, it is possible to set the output range of Group 0 or
Group 1 to be unipolar positive, unipolar negative, or bipolar,
either symmetrical or asymmetrical about 0 V. The DACs in the
AD5362/AD5363 are factory trimmed with the offset DACs set
at their default values. This gives the best offset and gain perfor-
mance for the default output range and span.
When the output range is adjusted by changing the value of the
offset DAC, an extra offset is introduced due to the gain error of
the offset DAC. The amount of offset is dependent on the mag-
nitude of the reference and how much the offset DAC moves
from its default value. See the Specifications section for this
offset. The worst-case offset occurs when the offset DAC is at
positive or negative full scale. This value can be added to the
offset present in the main DAC channel to give an indication of
the overall offset for that channel. In most cases, the offset can
be removed by programming the C register of the channel with
an appropriate value. The extra offset caused by the offset DAC
needs to be taken into account only when the offset DAC is
changed from its default value. Figure 22 shows the allowable
code range that can be loaded to the offset DAC, depending on
the reference value used. Thus, for a 5 V reference, the offset
DAC should not be programmed with a value greater than 8192
(0x2000).
5
4
3
2
1
0
0
Figure 22. Offset DAC Code Range
4096
OFFSET DAC CODE
8192
AD5362/AD5363
12288
RESERVED
16383