Datasheet

www.ti.com
SERIAL-DATA OUTPUT
DIGITAL TIMING
DIGITAL INPUT CODING
I
OUT



V
REF
H  V
REF
L
R
SENSE



N
65, 536




V
REF
LR
SENSE

(2)
V
OUT
 V
REF
L 

V
REF
H  V
REF
L

 N
65, 536
(1)
DIGITALLY-PROGRAMMABLE CURRENT
DAC7634
SBAS134B – JULY 2004 – REVISED DECEMBER 2005
Table 2. Serial Shift Register Truth Table
CS
(1)
CLK
(1)
LOAD RST SERIAL SHIFT REGISTER
H
(2)
X
(3)
H H No Change
L
(4)
L H H No Change
L ↑
(5)
H H Advanced One Bit
↑ L H H Advanced One Bit
H
(6)
X L
(7)
H No Change
H
(6)
X H ↑
(8)
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 SOURCE
register's output. For DAC7634, the SDO is a driven
The DAC7634 offers a unique set of features that
output and does not require an external pull-up. Any
allows a wide range of flexibility in designing
number of DAC7634s can be daisy-chained by
applications circuits such as programmable current
connecting the SDO pin of one device to the SDI pin
sources. The DAC7634 offers both a differential
of the following device in the chain, as shown in
reference input, as well as an open-loop configuration
Figure 61 .
around the output amplifier. The open-loop
configuration around the output amplifier allows a
transistor to be placed within the loop to implement a
digitally- programmable, unidirectional current source.
Figure 62 and Table 3 provide detailed timing for the
The availability of a differential reference allows
digital interface of the DAC7634.
programmability for both the full-scale and zero-scale
currents. The output current is calculated as:
The DAC7634 input data is in straight binary format.
The output voltage is given by Equation 1 .
Where N is the digital input code. This equation does
not include the effects of offset (zero-scale) or gain
(full-scale) errors.
23