LTC1409 LINER [Linear Technology], LTC1409 Datasheet - Page 13

• Manufacturer Part Number: LTC1409
• Description: 12-Bit, 800ksps Sampling A/D Converter with Shutdown
• Manufacturer: LINER [Linear Technology]

however, the bipolar zero error (BZE) will vary. The change
in BZE is typically less than 0.1% of the common mode
voltage. Dynamic performance is also affected by the
common mode voltage. THD will degrade as the inputs
approach either power supply rail, from 86dB with a
common mode of 0V to 75dB with a common mode of
2.5V or – 2.5V.
Differential inputs allow greater flexibility for accepting
different input ranges. Figure 10b shows a circuit that
converts a 0V to 5V analog input signal with no additional
translation circuitry.
Full-Scale and Offset Adjustment
Figure 11a shows the ideal input/output characteristics for
the LTC1409. The code transitions occur midway between
successive integer LSB values (i.e., –FS + 0.5LSB, –FS +
1.5LSB, –FS + 2.5LSB,. FS – 1.5LSB, FS – 0.5LSB).
A
PPLICATI
Figure 10b. Selectable 0V to 5V or 2.5V Input Range
0V TO 5V
RANGE
2.5V RANGE
80
70
60
50
40
30
20
10
Figure 10a. CMRR vs Input Frequency
0
1
ANALOG INPUT
O
U
10
2.5V
INPUT FREQUENCY (Hz)
1 F
S
10 F
I FOR ATIO
U
100
1
2
3
4
5
+A
–A
V
REFCOMP
AGND
REF
IN
IN
LTC1409
1000
W
LTC1409 • TPC09
LTC1409 • F10b
10000
U
The output is two’s complement binary with 1LSB =
FS – (– FS)/4096 = 5V/4096 = 1.22mV.
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. Figure 11b
shows the extra components required for full-scale error
adjustment. Zero offset is achieved by adjusting the offset
applied to the – A
0.61mV (i.e., – 0.5LSB) at +A
– A
0000 0000 and 1111 1111 1111. For full-scale adjust-
ment, an input voltage of 2.49817V (FS/2 – 1.5LSBs) is
applied to A
flickers between 0111 1111 1110 and 0111 1111 1111.
IN
50k
R1
input until the output code flickers between 0000
– 5V
111...111
111...110
111...101
000...010
000...001
000...000
Figure 11b. Offset and Full-Scale Adjust Circuit
Figure 11a. LTC1409 Transfer Characteristics
R5
47k
–(FS – 1LSB)
IN
50k
R2
and R2 is adjusted until the output code
24k
R3
IN
R6
24k
10 F
input. For zero offset error apply –
ANALOG INPUT
INPUT RANGE
100
R4
IN
and adjust the offset at the
1
2
3
4
5
+A
–A
V
REFCOMP
AGND
REF
FS – 1LSB
LTC1409 • F11a
IN
IN
LTC1409
LTC1409
LTC1409 • F11b
13