Datasheet

LTC2757
13
2757f
1. Load ±5V range with the output at 0V. Note that since span and code are updated together, the output, if started at
0V, will stay there. The 18-bit DAC code is shown in hex for compactness.
OPERATION
WR
2757 TD03
SPAN I/O
INPUT
DATA I/O
INPUT
UPD
D/S
20000
H
010
READ = LOW
V
OUT
UPDATE
(±5V RANGE, V
OUT
= 0V)
0V (00000
H
IN 0V to 5V RANGE) 0V (20000
H
IN ±5V RANGE)
The offset adjust pin V
OSADJ
can be used to null unipolar
offset or bipolar zero error. The offset change expressed
in LSB is the same for any output range:
ΔV
OS
LSB
[]
=
–V(V
OSADJ
)
V(R
IN
)
• 2048
A 5V control voltage applied to V
OSADJ
produces ΔV
OS
=
–2048 LSB in any output range, assuming a 5V reference
voltage at R
IN
.
In voltage terms, the offset delta is attenuated by a factor
of 32, 64 or 128, depending on the output range. (These
functions hold regardless of reference voltage.)
ΔV
OS
= –(
1
/
128
)V
OSADJ
[0V to 5V, ±2.5V spans]
ΔV
OS
= –(
1
/
64
)V
OSADJ
[0V to 10V, ±5V, –2.5V to
7.5V spans]
ΔV
OS
= –(
1
/
32
)V
OSADJ
[±10V span]
The gain error adjust pin GE
ADJ
can be used to null gain
error or to compensate for reference errors. The gain er-
ror change expressed in LSB is the same for any output
range:
ΔGE =
V(GE
ADJ
)
V(R
IN
)
• 2048
The gain-error delta is non-inverting for positive reference
voltages.
Note that this pin compensates the gain by altering the
inverted reference voltage V(REF). In voltage terms,
the V(REF) delta is inverted and attenuated by a factor
of 128.
ΔV(REF) = –(
1
/
128
)GE
ADJ
The nominal input range of these pins is ±5V; other volt-
ages of up to ±15V may be used if needed. However, do
not use voltages divided down from power supplies; ref-
erence-quality, low-noise inputs are required to maintain
the best DAC performance.
The V
OSADJ
pin has an input impedance of 1.28M. This
pin should be driven with a Thevenin-equivalent impedance
of 10k or less to preserve the settling performance of the
LTC2757. It should be shorted to GND if not used.
The GE
ADJ
pin has an input impedance of 2.56M, and
is intended for use with fi xed reference voltages only. It
should be shorted to GND if not used.
OPERATION—EXAMPLES