DAC8734_091 Datasheet, PDF (20/41 Pages) Texas Instruments – Quad, 16-Bit, High-Accuracy, ±16V Output, Serial Input DIGITAL-TO-ANALOG CONVERTER

DAC8734
SBAS465A – MAY 2009 – REVISED SEPTEMBER 2009 .................................................................................................................................................. www.ti.com
TRANSFER FUNCTION FOR THE ANALOG OUTPUTS (V_OUT-0 to V_OUT-3)
For bipolar output:
V_OUT = Gain ´ V_REF ´
INPUT_CODE ₊ ZERO_CODE
65536
8 ´ 65536
´
1 + ^GAIN_CODE
2 ´ 65536
(1)
For unipolar output:
V_OUT = Gain ´ V_REF ´
INPUT_CODE ₊ ZERO_CODE
65536
8 ´ 65536
´
1 + ^GAIN_CODE
65536
(2)
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.
Input Data Format
For bipolar output operation, INPUT_CODE is always twos complement, and can accept values between –32768
to 32767.
For unipolar output operation, INPUT_CODE is always straight binary, and can accept values between 0 to
65535.
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.
OUTPUT RANGE
Each channel of the DAC8734 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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