Datasheet

LTC1272
11
1272fc
For more information www.linear.com/1272
APPLICATIONS INFORMATION
Unipolar Operation
Figure 9 shows the ideal input/output characteristic for the
0V to 5V input range of the LTC1272. The code transitions
occur midway between successive integer LSB values
(i.e., 1/2LSB, 3/2LSBs, 5/2LSBs . . . FS – 3/2LSBs). The
output code is natural binary with 1 LSB = FS/4096 =
(5/4096)V = 1.22mV.
Unipolar Offset and Full-Scale Error Adjustment
In applications where absolute accuracy is important, then
offset and full-scale error can be adjusted to zero. Offset
error must be adjusted before full-scale error. Figure 10
shows the extra components required for full-scale error
adjustment. Zero offset is achieved by adjusting the offset
of the op amp driving A
IN
(i.e., A1 in Figure 10). For zero
offset error apply 0.61mV (i.e., 1/2LBS) at V
IN
and adjust
the op amp offset voltage until the ADC output code flickers
between 0000 0000 0000 and 0000 0000 0001.
For zero full-scale error apply an analog input of 4.99817V
(i.e., FS – 3/2LSBs or last code transition) at V
IN
and adjust
R1 until the ADC output code flickers between 1111 1111
1110 and 1111 1111 1111.
Figure 8. LTC1272 Internal 2.42V Reference Figure 9. LTC1272 Ideal Input/Output Transfer Characteristic
Figure 7. Operating Waveforms Using an External Clock Source for CLK IN
LTC1272 • F07
CS & RD
BUSY
CLK IN
50ns TYP
DB0
(LSB)
DB1DB10DB11
(MSB)
CLK OUT
LTC1272 • F08
–
+
CURVATURE
CORRECTED
BANDGAP
REFERENCE
TO DAC
V
REF
AGND
5V
LTC1272
0.1µF
10µF
+
3
2
OUTPUT CODE
A
IN
, INPUT VOLTAGE (IN TERMS OF LSBs)
0
00...000
00...001
00...010
00...011
11...110
11...111
1 FS
LT1272 • F09
2 3
11...101
LSB
LSBs
LSBs
FS – 1LSB
FS = 5V
1LSB =
FS
––––
4096
FULL-SCALE
TRANSITION