Datasheet
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OUTPUT RANGE
V V-
REFH REFL
65536
´ CODE BufferGain+V´
REFL
V
OUT
=
(1)
INPUT DATA FORMAT
POWER DOWN
HARDWARE RESET
DAC8881
SBAS422A – JULY 2007 – REVISED SEPTEMBER 2007
The maximum output range of the DAC8881 is V
REFL
to V
REFH
× G, where G is the output buffer gain set by the
GAIN pin. When the GAIN pin is connected to DGND, the output buffer gain = 1. When the GAIN pin is
connected to IOV
DD
, the output buffer gain = 2. The output range must not be greater than AV
DD
; otherwise,
output saturation occurs. The DAC8881 output transfer function is given in Equation 1 :
Where:
CODE = 0 to 65535. This is the digital code loaded to the DAC.
Buffer Gain = 1 or 2 (set by the GAIN pin).
V
REFH
= reference high voltage applied to the device.
V
REFL
= reference low voltage applied to the device.
The USB/ BTC pin defines the input data format. When this pin is connected to IOV
DD
, the input data format is
straight binary, as shown in Table 1 . When this pin is connected to DGND, the input data format is two's
complement, as shown in Table 2 .
Table 1. Output vs Straight Binary Code
USB CODE 5V RANGE DESCRIPTION
FFFFh +4.99992 +Full-Scale – 1LSB
C000h +3.75000 3/4-Scale
8000h +2.50000 Midscale
4000h +1.25000 1/4-Scale
0000h 0.00000 Zero-Scale
Table 2. Output vs Two's Complement Code
BTC CODE 5V RANGE DESCRIPTION
7FFFh +4.99992 +Full-Scale – 1LSB
4000h +3.75000 3/4-Scale
0000h +2.50000 Midscale
FFFFh +2.49992 Midscale – 1LSB
C000h +1.25000 1/4-Scale
8000h 0.00000 Zero-Scale
The DAC8881 has a hardware power-down function. When the PDN pin is high, the device is in power-down
mode. The V
OUT
pin is connected to ground through an internal 10k Ω resistor, but the contents of the input
register and the DAC latch do not change. In power-down mode, SPI communication is still active.
When the RST pin is low, the device is in hardware reset mode, and the input register and DAC latch are set to
the value defined by the RSTSEL pin. After RST goes high, the device is in normal operating mode.
26 Submit Documentation Feedback Copyright © 2007, Texas Instruments Incorporated
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