Datasheet

13
LTC1418
APPLICATIONS INFORMATION
WUU
U
Figure 9a. LTC1418 Unipolar Transfer Characteristics
ANALOG INPUT
1418 F10a
5V
R4
100Ω
R2
50k
R3
24k
R7
48k
R6
24k
R1
50k
R5
47k
0.1µF
10µF
R8
100Ω
1
2
3
4
5
LTC1418
A
IN
+
A
IN
–
V
REF
REFCOMP
AGND
V
SS
V
DD
Figure 10a. Offset and Full-Scale Adjust Circuit
If –5V Is Not Available
UNIPOLAR / BIPOLAR OPERATION AND ADJUSTMENT
Figure 9a shows the ideal input/output characteristics for
the LTC1418. 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 natural binary
with 1LSB = FS/16384 = 4.096V/16384 = 250µV. Figure 9b
shows the input/output transfer characteristics for the
bipolar mode in two’s complement format.
Unipolar Offset and Full-Scale Error Adjustment
In applications where absolute accuracy is important,
offset and full-scale errors can be adjusted to zero. Offset
error must be adjusted before full-scale error. Figures
10a and 10b show the extra components required for full-
scale error adjustment. Zero offset is achieved by adjust-
ing the offset applied to the A
IN
–
input. For zero offset
error apply 125µV (i.e., 0.5LSB) at the input and adjust
the offset at the A
IN
–
input until the output code flickers
between 0000 0000 0000 00 and 0000 0000 0000 01. For
full-scale adjustment, an input voltage of 4.095625V
(FS – 1.5LSBs) is applied to A
IN
+
and R2 is adjusted until
the output code flickers between 1111 1111 1111 10 and
1111 1111 1111 11.
Bipolar Offset and Full-Scale Error Adjustment
Bipolar offset and full-scale errors are adjusted in a similar
fashion to the unipolar case. Again, bipolar offset error
must be adjusted before full-scale error. Bipolar offset
Figure 9b. LTC1418 Bipolar Transfer Characteristics
Figure 10b. Offset and Full-Scale Adjust Circuit
If –5V Is Available
INPUT VOLTAGE (V)
0V
OUTPUT CODE
–1
LSB
1418 F9b
011...111
011...110
000...001
000...000
100...000
100...001
111...110
1
LSB
BIPOLAR
ZERO
111...111
FS/2 – 1LSB–FS/2
FS = 4.096V
1LSB = FS/16384
ANALOG INPUT
1418 F10b
5V–5V
–5V
1N5817
R4
100Ω
R2
50k
R3
24k
R6
24k
R1
50k
R5
47k
0.1µF
*
*ONLY NEEDED IF V
SS
GOES
ABOVE GROUND
10µF
1
2
3
4
5
LTC1418
A
IN
+
A
IN
–
V
REF
REFCOMP
AGND
V
SS
V
DD
INPUT VOLTAGE (V)
0V
OUTPUT CODE
FS – 1LSB
1418 F9a
111...111
111...110
111...101
111...100
000...000
000...001
000...010
000...011
1
LSB
UNIPOLAR
ZERO
1LSB =
FS
16384
4.096V
16384
=