LTC1282ACS View Datasheet(PDF) - Linear Technology
Part Name
Description
MFG CO.
'LTC1282ACS' PDF : 24 Pages View PDF
LTC1282
APPLICATI S I FOR ATIO
apply 0.305mV (i.e., 1/2LSB) at V1 and adjust the op amp
offset voltage until the LTC1282 output code flickers
between 0000 0000 0000 and 0000 0000 0001. For zero
full scale error, apply an analog input of 2.49909V
(i.e., FS – 1 1/2LSBs or last code transition) at the input
and adjust the full scale trim until the LTC1282 output code
flickers between 1111 1111 1110 and 1111 1111 1111.
R1
50Ω
V1
+
A1
–
R4
R2
100Ω
10k
R5
10k
FULL SCALE
ADJUST
ADDITIONAL PINS OMITTED FOR CLARITY
±20LSB TRIM RANGE
AIN
LTC1282
AGND
LTC1282 • F10
Figure 10. Full Scale Adjust Circuit
R1
ANALOG 10k
INPUT
+
0V TO 2.5V
R2
10k 10k
5V
–
R9
20Ω
AIN
R4
100k
R5
4.3k
FULL SCALE
ADJUST
R3
100k
R7
100k
R6
400Ω
LTC1282
5V
R8
10k
OFFSET
ADJUST
LTC1282 • F11
Figure 11. Unipolar Offset and Full Scale Adjust Circuit
Bipolar Offset and Full Scale Adjustment
Bipolar offset and full scale errors are adjusted in a similar
fashion to the unipolar case. Figure 10 shows the extra
components required for full scale error adjustment. If both
offset and full scale adjustments are needed, the circuit in
Figure 12 can be used. Again, bipolar offset must be adjusted
before full scale error. Bipolar offset error adjustment is
R1
ANALOG 10k
INPUT
±1.25V
+
R2
10k
–
AIN
R4
100k
R5
4.3k
LTC1282
FULL SCALE
ADJUST
R3
100k
R7
100k
5V
R8
20k
LTC1282 • F12
OFFSET
R6
ADJUST
200Ω
– 5V
Figure 12. Bipolar Offset and Full Scale Adjust Circuit
achieved by trimming the offset adjustment of Figure 12
while the input voltage is 1/2LSB below ground. This is done
by applying an input voltage of – 0.305mV (– 1/2LSB for
LTC1282) to the input in Figure 12 and adjusting R8 until the
ADC output code flickers between 0000 0000 0000 and
1111 1111 1111. For full scale adjustment, an input voltage
of 1.24909V (FS – 3/2LSBs for LTC1282) is applied to the
input and R5 is adjusted until the output code flickers
between 0111 1111 1110 and 0111 1111 1111.
BOARD LAYOUT AND BYPASSING
The LTC1282 is easy to use. To obtain the best perfor-
mance from the device, a printed circuit board is
recommended. Layout for the printed circuit board should
ensure that digital and analog signal lines are separated as
much as possible. In particular, care should be taken not
to run any digital track alongside an analog signal track or
underneath the ADC. The analog input should be screened
by AGND.
High quality tantalum and ceramic bypass capacitors
should be used at the VDD and VREF pins as shown in Figure
13. In bipolar mode, a 0.1µF ceramic provides adequate
bypassing for the VSS pin. The capacitors must be located
as close to the pins as possible. The traces connecting the
pins and the bypass capacitors must be kept short and
should be made as wide as possible.
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