LTC1402
U
W U U
APPLICATIONS INFORMATION
more than 0.25 inch long to the common reference. You
may also choose to tie AGND2 (Pin 6) directly to a solid
analog ground plane and eliminate all the 10µF capacitors
at this pin. The external reference source needs to have
enough output drive current for the 2kΩ load at each ADC.
Adjustment in Unipolar Mode with Pin 8 Held Low
The code transitions occur midway between successive
integer LSB values (i.e., –FS + 0.5LSB, –FS + 1.5LSB,
–FS + 2.5LSB,...FS – 2.5LSB, FS – 1.5LSB). The output at
DOUT is binary with 1LSB = FS/4096 = 4.096V/4096 =
1.0mV. In applications where absolute accuracy is impor-
tant, offset and full-scale errors can be adjusted to zero.
Offset error must be adjusted before full-scale error. In
Figure 10b, zero offset is achieved by adjusting the offset
FULL-SCALE AND OFFSET ADJUSTMENT
Figure 9 shows the ideal input/output characteristics for
the LTC1402 in bipolar mode and unipolar mode. Figure
10a shows the components required for full-scale error
adjustment. Figure 10b includes the components for off-
set and full-scale adjustment.
–
applied to the AIN input. For zero offset error apply
–0.5mV (i.e., –0.5LSB) to AIN+ and adjust the offset at the
AIN– input using R8 until the output code flickers between
R1
LTC1402
+
51Ω
3
4
A
A
011...111
011...110
011...101
111...111
111...110
111...101
IN
IN
ANALOG INPUT
0V TO 4.096V
OR ±2.048V
R2
39k
R3
51Ω
S/H
–
2.048V
BANGAP
REFERENCE
5
V
REF
REFERENCE
AMP
R4
470k
10µF
64k
64k
100...010
100...001
100...000
000...010
000...001
000...000
7
6
GAIN
R5
500Ω
AGND2
–(FS – 1LSB)
FS – 1LSB
INPUT VOLTAGE (V)
1402 F010a
1402 F09
Figure 9. LTC1402 Transfer Characteristic
Figure 10a. Full-Scale Adjustment Circuit with
±10LSB Range
Adjustment in Bipolar Mode with Pin 8 Held High
5V
The code transitions occur midway between successive
integerLSBvalues(i.e., –FS+0.5LSB, –FS+1.5LSB, –FS
+2.5LSB,...FS–2.5LSB, FS–1.5LSB). TheoutputatDOUT
is two’s complement binary with 1LSB = FS – (–FS)/4096
= 4.096V/4096 = 1.0mV. 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. In Figure 10b, zero offset is achieved by
R6
R1
LTC1402
+
–
24k
51Ω
3
4
A
A
IN
IN
ANALOG INPUT
0V TO 4.096V
OR ±2.048V
R2
24k
R3
51Ω
S/H
5V
R7
7.5k
2.048V
BANGAP
REFERENCE
OFFSET
ADJ
R8
10k
5
V
REF
REFERENCE
AMP
R4
470k
–
adjusting the offset applied to the AIN input. For zero
10µF
64k
64k
+
offset error, apply –0.5mV (i.e., –0.5LSB) to AIN and
adjust the offset at the AIN– input using R8 until the output
code flickers between 0000 0000 0000 and 1111 1111
1111. For full-scale adjustment in Figures 10a and 10b,
7
6
GAIN
FULL-SCALE
R5
ADJ 500Ω
AGND2
1402 F010b
+
apply an input voltage of 2.0465V (FS – 1.5LSB) to AIN
Figure 10b. Offset and Full-Scale Adjustment
Circuits with ±10LSB Range
and adjust R5 until the output code flickers between 0111
1111 1110 and 0111 1111 1111.
14
Linear [ Linear ]
