LTC1400 LINER [Linear Technology], LTC1400 Datasheet - Page 11

• Manufacturer Part Number: LTC1400
• Description: Complete SO-8, 12-Bit, 400ksps ADC with Shutdown
• Manufacturer: LINER [Linear Technology]

ANALOG
APPLICATIONS
Figure 10c. LTC1400 Bipolar Offset and Full-Scale Adjust Circuit
0V TO 4.096V
2.048V
INPUT
ANALOG
Figure 10b. LTC1400 Offset and Full-Scale Adjust Circuit
V
IN
INPUT
ADDITIONAL PINS OMITTED FOR CLARITY
20LSB TRIM RANGE
5V
Figure 10a. LTC1400 Full-Scale Adjust Circuit
10k
R1
50
R1
10k
10k
R1
R2
10k
R2
10k
R2
10k
R9
20
U
+
–
A1
R3
10k
INFORMATION
+
–
+
–
U
A1
A1
100
FULL-SCALE
R4
R4
100k
R5
4.3k
FULL-SCALE
ADJUST
R3
100k
R6
200
ADJUST
W
100k
R4
100k
R5
4.3k
FULL-SCALE
ADJUST
R3
100k
R6
400
R7
A
GND
100k
A
LTC1400
LTC1400
R7
–5V
IN
IN
5V
R8
20k
OFFSET
ADJUST
U
LTC1400 • F10a
A
LTC1400
LTC1400 • F10c
IN
5V
LTC1400 • F10b
R8
10k
OFFSET
ADJUST
error adjustment. Figure 10b shows offset and full-scale
adjustment. Offset error must be adjusted before full-
scale error. Zero offset is achieved by applying 0.5mV (i.e.,
0.5LSB) at the input and adjusting the offset trim until the
LTC1400 output code flickers between 0000 0000 0000
and 0000 0000 0001. For zero full-scale error, apply an
analog input of 4.0945V (FS – 1.5LSB or last code transi-
tion) at the input and adjust R5 until the LTC1400 output
code flickers between 1111 1111 1110 and 1111 1111
1111.
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.
BOARD LAYOUT AND BYPASSING
To obtain the best performance from the LTC1400, a
printed circuit board is required. 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 GND.
High quality tantalum and ceramic bypass capacitors
should be used at the V
Typical Application on the first page of this data sheet. For
the bipolar mode, a 0.1 F ceramic provides adequate
bypassing for the V
10 F surface mount AVX capacitor with a 0.1 F ceramic is
recommended for the V
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. In
unipolar mode operation, V
noise source before shorting to the GND pin.
SS
pin. For optimum performance, a
CC
CC
and V
and V
SS
should be isolated from any
REF
REF
pins as shown in the
pins. The capacitors
LTC1400
11