Datasheet

TRANSFER FUNCTION FOR THE ANALOG OUTPUTS (V
OUT
-0 to V
OUT
-3)
V =
OUT
Gain V´ ´
REF
INPUT_CODE
16384
+
ZERO_CODE
32 16384´
´
1+
GAIN_CODE
8 16384´
(1)
V =
OUT
Gain V´ ´
REF
INPUT_CODE
16384
+
ZERO_CODE
32 16384´
´
1+
GAIN_CODE
4 16384´
(2)
Input Data Format
OUTPUT RANGE
DAC8234
SBAS464A – AUGUST 2009 – REVISED SEPTEMBER 2009 ........................................................................................................................................... www.ti.com
For bipolar output:
For unipolar output:
Where:
GAIN is the DAC gain, which can be set to x2 or x4 and is determined by the connection of pins R
FB1
-x and
R
FB2
-x to V
OUT
-x, and the GAIN bit in the Command Register.
INPUT_CODE is the decimal equivalent value of the code written into the DAC input register.
ZERO_CODE is the decimal equivalent value of the code written into the Zero Register.
GAIN_CODE is the decimal equivalent value of the code written into the Gain Register.
Note that the output voltage must not be greater than (AV
DD
– 1.0V) or less than (AV
SS
+ 1.0V); otherwise, the
output may be saturated.
For bipolar output operation, INPUT_CODE is always twos complement, and can accept values between – 8192
to 8191.
For unipolar output operation, INPUT_CODE is always straight binary, and can accept values between 0 to
16383.
GAIN_CODE is always in twos complement format, and can accept values between – 128 and +127.
ZERO_CODE is always in twos complement format and can accept values between – 256 and +255.
The data written to the Command and Monitor registers are written as specified in the definitions. For read
operations, the read-back data format is the same as the format used to write to the device. Refer to the Internal
Registers section for more details.
Each channel of the DAC8234 implements an output amplifier that provides a unipolar output or a bipolar output
with a gain of 2 or 4. The output span equals the gain times the reference voltage. For a 5V reference, the output
range can be configured as ± 10V, ± 5V, 0V to 20V, or 0V to 10V. The status of the UNI/BIP pin determines the
output mode (unipolar or bipolar) of each group. When the UNI/BIP-A pin is high, the outputs of Group A (DAC-0
and DAC-1) are unipolar; when the pin is low, the outputs of Group A are bipolar. Similarly, the UNI/BIP-B pin
defines the output mode of Group B (DAC-2 and DAC-3).
Each individual DAC can be configured with a gain of 4 or a gain of 2. To set the gain = 4, connect R
FB1
-x to
V
OUT
-x with R
FB2
-x left open, and set the gain bit for that channel to '1' in the Command Register. To set the gain
= 2, connect both R
FB1
-x and R
FB2
-x to V
OUT
-x, and set the gain bit for that channel to '0'. The gain bits in the
Command Register are set to '1' by default at power-on or reset, and must be cleared to '0' for gain = 2.
Note that the power supplies must meet the following requirements:
• AV
DD
must not be greater than 24V or less than 4.75V, and AV
SS
must not be greater than – 4.75V or less
than – 18V. In any case, (AV
DD
– AV
SS
) ≤ 36V.
• For bipolar mode: AV
DD
≥ 2 × V
REF
+ 1V, and AV
SS
≤ – 2 × V
REF
– 1V.
• For unipolar mode: AV
DD
≥ Gain × V
REF
+ 1V, and AV
SS
≤ – 2 × V
REF
– 1V.
For example, for a 5V reference in bipolar operation, the minimum supplies must be at least ± 11V, regardless of
whether the output range is ± 5V or ± 10V. For unipolar operation with the same reference, the supplies must be
at least ± 11V for a 0V to 10V operation, and +21V/ – 11V for a 0V to +20V operation.
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