LTC1400
U U
W U
APPLICATIO S I FOR ATIO
trimmed to 2.42V. It is internally connected to the DAC
and is available at Pin 3 to provide up to 1mA of current to
an external load. For minimum code transition noise, the
reference output should be decoupled with a capacitor to
filterwidebandnoisefromthereference(10μFtantalumin
Unipolar/Bipolar Operation and Adjustment
Figure 8 shows the ideal input/output characteristics for
the LTC1400. The code transitions occur midway between
successive integer LSB values (i.e., 0.5LSB, 1.5LSB,
2.5LSB, … FS – 1.5LSB). The output code is straight
binary with 1LSB = 4.096V/4096 = 1mV. Figure 9 shows
the input/output transfer characteristics for the bipolar
mode in two’s complement format.
parallel with a 0.1μF ceramic). The V pin can be driven
REF
with a DAC or other means to provide input span adjust-
ment in bipolar mode. The V
pin must be driven to at
REF
least 2.45V to prevent conflict with the internal reference.
The reference should not be driven to more than 5V.
FS
4096
1LSB =
111...111
111...110
111...101
111...100
Figure 6 shows an LT1360 op amp driving the reference
pin. Figure 7 shows a typical reference, the LT1019A-5
connected to the LTC1400. This will provide an improved
drift (equal to the maximum 5ppm/°C of the LT1019A-
5) and a ±4.231V full scale. If V
is forced lower than
REF
UNIPOLAR
ZERO
2.42V, the REFRDY bit in the serial data output will be
000...011
000...010
000...001
000...000
forced to low.
5V
INPUT RANGE
0V
1
LSB
V
FS – 1LSB
CC
A
V
IN
±0.846 • V
REF(OUT)
INPUT VOLTAGE (V)
1400 F08
+
LTC1400
V
≥ 2.45V
3Ω
REF(OUT)
LT1360
Figure 8. LTC1400 Unipolar Transfer Characteristics
REF
–
10µF
011...111
GND
V
SS
BIPOLAR
ZERO
011...110
–5V
1400 F06
000...001
000...000
111...111
111...110
Figure 6. Driving the V
with the LT1360 Op Amp
REF
5V
100...001
100...000
INPUT RANGE ±4.231V
(= ±0.846 • V
V
CC
A
V
IN
)
REF
10V
LTC1400
–1 0V
1
–FS/2
FS/2 – 1LSB
V
LSB
LSB
IN
V
REF
OUT
INPUT VOLTAGE (V)
11400 F09
3Ω
10µF
LT1019A-5
GND
Figure 9. LTC1400 Bipolar Transfer Characteristics
GND
V
SS
Unipolar Offset and Full-Scale Error Adjustments
–5V
1400 F07
In applications where absolute accuracy is important,
offset and full-scale errors can be adjusted to zero. Figure
10a shows the extra components required for full-scale
Figure 7. Supplying a 5V Reference Voltage
to the LTC1400 with the LT1019A-5
1400fa
10
Linear [ Linear ]
