Datasheet

14
LTC1603
1603f
APPLICATIONS INFORMATION
WUU
U
LTC1603
A
IN
+
ANALOG INPUT
2V TO 2.7V
DIFFERENTIAL
A
IN
–
V
REF
REFCOMP
AGND
1603 F13
1
2
3
4
5
47µF
LTC1450
2V TO 2.7V
Figure 14a. CMRR vs Input Frequency
INPUT FREQUENCY (Hz)
1k
COMMON MODE REJECTION (dB)
80
70
60
50
40
30
20
10
0
10k 100k
1603 G14a
1M
Figure 13. Driving V
REF
with a DAC
can not exceed the AV
DD
or V
SS
power supply voltages.
Integral nonlinearity errors (INL) and differential nonlin-
earity errors (DNL) are independent of the common mode
voltage, 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 96dB
with a common mode of 0V to 86dB with a common mode
of 2.5V or –2.5V.
Differential inputs allow greater flexibility for accepting
different input ranges. Figure 14b shows a circuit that
converts a 0V to 5V analog input signal with only an
additional buffer that is not in the signal path.
LTC1603
A
IN
+
A
IN
–
V
REF
0V TO
5V
±2.5V
REFCOMP
AGND
1603 F14b
1
2
3
4
5
10µF
ANALOG INPUT
–
+
Figure 14b. Selectable 0V to 5V or ±2.5V Input Range
Full-Scale and Offset Adjustment
Figure 15a shows the ideal input/output characteristics
for the LTC1603. 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). The output is two’s complement binary with
1LSB = FS – (–FS)/65536 = 5V/65536 = 76.3µV.
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 15b
shows the extra components required for full-scale error
adjustment. Zero offset is achieved by adjusting the offset
applied to the A
IN
–
input. For zero offset error apply
1603 F15a
011...111
011...110
000...001
000...000
111...111
111...110
100...001
100...000
FS – 1LSB
–(FS – 1LSB)
INPUT VOLTAGE (A
IN
+
– A
IN
–
)
OUTPUT CODE
Figure 15a. LTC1603 Transfer Characteristics