LTC1402 Linear Technology, LTC1402 Datasheet - Page 13

• Manufacturer Part Number: LTC1402
• Description: Serial 12-Bit/ 2.2Msps Sampling ADC with Shutdown
• Manufacturer: Linear Technology

APPLICATIONS
FULL-SCALE AND OFFSET ADJUSTMENT
Figure 8 shows the ideal input/output characteristics for
the LTC1402 in bipolar mode and unipolar mode. Figure 9a
shows the components required for full-scale error ad-
justment. Figure 9b includes the components for offset
and full-scale adjustment.
Adjustment in Bipolar Mode with Pin 8 Held High
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 D
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 9b, zero offset is achieved by adjust-
ing the offset applied to the A
error, apply – 0.5mV (i.e., – 0.5LSB) to A
offset at the A
flickers between 0000 0000 0000 and 1111 1111 1111.
For full-scale adjustment in Figures 9a and 9b, apply an
input voltage of 2.0465V (FS – 1.5LSB) to A
R5 until the output code flickers between 0111 1111 1110
and 0111 1111 1111.
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
– 20
– 30
– 40
– 50
– 60
–10
–70
0
0.1
Figure 7. CMRR vs Input Frequency
IN
–
input using R8 until the output code
U
1
FREQUENCY (MHz)
INFORMATION
U
10
IN
–
100
input. For zero offset
W
IN
1402 F07
+
1000
and adjust the
IN
+
and adjust
U
OUT
ANALOG INPUT
ANALOG INPUT
FULL-SCALE
OFFSET
0V TO 4.096V
0V TO 4.096V
Figure 9a. Full-Scale Adjustment Circuit with 10LSB Range
OR 2.048V
OR 2.048V
ADJ
ADJ
10k
R8
011...111
011...110
011...101
100...010
100...001
100...000
500
Figure 9b. Offset and Full-Scale Adjustment
Circuits with 10LSB Range
5V
500
R5
Figure 8. LTC1402 Transfer Characteristic
R5
– (FS – 1LSB)
51
51
R1
R3
7.5k
51
51
R4
470k
R7
R1
R3
R4
470k
5V
R2
39k
10 F
R6
24k
R2
24k
10 F
3
4
5
7
6
INPUT VOLTAGE (V)
3
4
5
7
6
AGND2
A
A
V
GAIN
AGND2
A
A
V
GAIN
IN
IN
REF
IN
IN
REF
+
–
+
–
REFERENCE
S/H
REFERENCE
S/H
64k
64k
64k
64k
AMP
AMP
FS – 1LSB
1402 F08
2.048V
2.048V
LTC1402
111...111
111...110
111...101
000...010
000...001
000...000
REFERENCE
REFERENCE
BANGAP
BANGAP
LTC1402
13
LTC1402
1402 F09a
1402 F09b