14
LTC1404
1404fa
APPLICATIONS INFORMATION
WU
U
Figure 8. LTC1404 Unipolar Transfer Characteristics
INPUT VOLTAGE (V)
0V
OUTPUT
CODE
FS – 1LSB
1404 F08
111...111
111...110
111...101
111...100
000...000
000...001
000...010
000...011
1
LSB
UNIPOLAR
ZERO
1LSB = FS
4096
4.096
4096
=
Figure 10b. LTC1404 Offset and Full-Scale Adjust Circuit
1404 F10b
–
+
R2
10k
R9
20
R4
100k
R5
4.3k
FULL-SCALE
ADJUST
R3
100k
R6
400
R1
10k
ANALOG
INPUT
0V TO 4.096V
A1
5V
R8
10k
OFFSET
ADJUST
R7
100k
5V
AIN
LTC1404
Bipolar Offset and Full-Scale Error Adjustments
Bipolar offset and full-scale errors are adjusted in a similar
fashion to the unipolar case. Bipolar offset error adjust-
ment is achieved by applying an input voltage of – 0.5mV
(– 0.5LSB) to the input in Figure 10c and adjusting the op
amp until the ADC output code flickers between 0000 0000
0000 and 1111 1111 1111. For full-scale adjustment, an
input voltage of 2.0465V (FS – 1.5LSBs) is applied to the
input and R5 is adjusted until the output code flickers
between 0111 1111 1110 and 0111 1111 1111.
1404 F10c
–
+
R2
10k
R4
100k
R5
4.3k
FULL-SCALE
ADJUST
R3
100k
R6
200
R1
10k
ANALOG
INPUT
±2.048V
A1
R8
20k
OFFSET
ADJUST
R7
100k
5V
–5V
AIN
LTC1404
Figure 10c. LTC1404 Bipolar Offset and Full-Scale Adjust Circuit
Figure 9. LTC1404 Bipolar Transfer Characteristics
INPUT VOLTAGE (V)
0V
OUTPUT
CODE
–1
LSB
1404 F09
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
1404 F10a
–
+
R2
10k
R3
10k
R1
50
R4
100
FULL-SCALE
ADJUST
VIN
A1
LTC1404
AIN
GND
ADDITIONAL PINS OMITTED FOR CLARITY
±20LSB TRIM RANGE
Figure 10a. LTC1404 Full-Scale Adjust Circuit