DAC7634
www.ti.com
SBAS134A–JULY 2004–REVISED AUGUST 2004
SERIAL-DATA OUTPUT
Table 2. Serial Shift Register Truth Table
(1)
CS
CLK(1)
X(3)
L
LOAD
RST
H
SERIAL SHIFT REGISTER
H(2)
L(4)
L
H
H
No Change
No Change
H
(5)
↑
H
H
Advanced One Bit
Advanced One Bit
No Change
↑
L
X
X
H
L(7)
H
H(6)
H(6)
H
(8)
H
↑
No Change
(1) CS and CLK are interchangeable.
(2) H = Logic HIGH
(3) X = Don't Care
(4) L = Logic LOW
(5) Positive logic transition
(6) A HIGH value is suggested in order to avoid a false clock from advancing the shift register and
changing the shift register.
(7) If data is clocked into the serial register while LOAD is LOW, the selected DAC register changes as
the shift register bits flow through A1 and A0. This corrupts the data in each DAC register that has
been erroneously selected.
(8) Rising edge of RST causes no change in the contents of the serial shift register.
The Serial-Data Output (SDO) is the internal shift
ǒVREF
LǓ
H * V
N
REF
65, 536
register's output. For DAC7634, the SDO is a driven
output and does not require an external pull-up. Any
number of DAC7634s can be daisy-chained by con-
necting the SDO pin of one device to the SDI pin of
the following device in the chain, as shown in
Figure 61.
V
+ V
L )
OUT
REF
(1)
DIGITALLY-PROGRAMMABLE CURRENT
SOURCE
The DAC7634 offers a unique set of features that
allows a wide range of flexibility in designing appli-
cations circuits such as programmable current
sources. The DAC7634 offers both a differential
reference input, as well as an open-loop configuration
around the output amplifier. The open-loop configur-
ation around the output amplifier allows a transistor to
be placed within the loop to implement a digitally-
programmable, unidirectional current source. The
DIGITAL TIMING
Figure 62 and Table 3 provide detailed timing for the
digital interface of the DAC7634.
DIGITAL INPUT CODING
The DAC7634 input data is in straight binary format.
The output voltage is given by Equation 1.
availability of
a
differential reference allows
programmability for both the full-scale and zero-scale
currents. The output current is calculated as:
Where N is the digital input code. This equation does
not include the effects of offset (zero-scale) or gain
(full-scale) errors.
V
H * V
L
REF
R
REF
N
ǒ Ǔ
I
+
ǒ
Ǔ
ƪ
ƫ
OUT
65, 536
SENSE
) ǒVREF SENSEǓ
LńR
(2)
23
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