ANALOG OUTPUTS
The current into the VREFH input depends on the DAC output
voltages and can vary from a few microamps to approxi-
mately 0.1 milliamp. The VREFH source will not be required
to sink current, only source it. Bypassing the reference
voltage or voltages with at least a 0.1µF capacitor placed as
close to the DAC7613 package is strongly recommended.
When VSS = –5V (dual supply operation), the output ampli-
fier can swing to within 2.25V of the supply rails, guaran-
teed over the –40°C to +85°C temperature range. With
VSS = 0V (single-supply operation), the output can swing to
ground. Note that the settling time of the output op amp will
be longer with voltages very near ground. Additionally, care
must be taken when measuring the zero-scale error when
VSS = 0V. Since the output voltage cannot swing below
ground, the output voltage may not change for the first few
digital input codes (000H, 001H, 002H, etc.) if the output
amplifier has a negative offset.
DIGITAL INTERFACE
Table I shows the basic control logic for the DAC7613. Note
that the internal register is level triggered and not edge
triggered. When the appropriate signal is LOW, the register
becomes transparent. When this signal is returned HIGH, the
digital word currently in the register is latched. The first
register (the input register) is triggered via the R/W, and CS
inputs. The second register (the DAC register) is transparent
when LOADDAC input is pulled LOW.
The behavior of the output amplifier can be critical in some
applications. Under short-circuit conditions (DAC output
shorted to ground), the output amplifier can sink a great deal
more current than it can source. See the Specifications table
for more details concerning short-circuit current.
The double-buffered architecture is mainly designed so that
the DAC input register can be written at any time and then
the DAC voltage updated by pulling LOADDAC LOW.
REFERENCE INPUTS
The reference inputs, VREFL and VREFH, can be any voltage
between VSS + 2.25V and VDD – 2.25V provided that VREFH
is at least 1.25V greater than VREFL. The minimum output of
each DAC is equal to VREFL plus a small offset voltage
(essentially, the offset of the output op amp). The maximum
output is equal to VREFH plus a similar offset voltage. Note
that VSS (the negative power supply) must either be
connected to ground or must be in the range of –4.75V to
–5.25V. The voltage on VSS sets several bias points within
the converter. If VSS is not in one of these two configura-
tions, the bias values may be in error and proper operation
of the device is not guaranteed.
INPUT
REGISTER
DAC
REGISTER
R/W
CS
RST LOADDAC
MODE
L
L
L
L
H
H
H
H
H
L
L
H
H
L
Write
Write
Read
Hold
Hold
Hold
Write
Hold
Write
Write Input
Read Input
Update
H
X
X
X
L
Hold
H
H
H
Update
Hold
H
X
Hold
Reset
Reset
X = Don’t Care.
TABLE I. DAC7613 Control Logic Truth Table.
®
8
DAC7613
TI [ TEXAS INSTRUMENTS ]
