LT1460-2.5 LINER [Linear Technology], LT1460-2.5 Datasheet - Page 13

• Manufacturer Part Number: LT1460-2.5
• Description: Serial 12-Bit/14-Bit, 2.8Msps
• Manufacturer: LINER [Linear Technology]

APPLICATIONS INFORMATION
internal reference. The recommended range for an external
reference is 2.55V to V
will see a DC quiescent load of 0.75mA and as much as
3mA during conversion.
INPUT SPAN VERSUS REFERENCE VOLTAGE
The differential input range has a unipolar voltage span
that equals the difference between the voltage at the ref-
erence buffer output V
ground (Exposed Pad Ground). The differential input range
of the ADC is ±1.25V when using the internal reference.
The internal ADC is referenced to these two nodes. This
relationship also holds true with an external reference.
DIFFERENTIAL INPUTS
The LTC1403-1/LTC1403A-1 have a unique differential
sample-and-hold circuit that allows inputs from ground
to V
ence of A
voltage at the inputs. The common mode rejection holds
up at extremely high frequencies, see Figure 4. The only
requirement is that both inputs not go below ground or
exceed V
ential nonlinearity errors (DNL) are largely independent
of the common mode voltage. However, the offset error
will vary. The change in offset error is typically less than
0.1% of the common mode voltage.
DD
. The ADC will always convert the bipolar differ-
DD
–100
–120
IN
–20
–40
–60
–80
. Integral nonlinearity errors (INL) and differ-
+
0
100
– A
IN
1k
–
CMRR vs Frequency
, independent of the common mode
10k
REF
DD
FREQUENCY (Hz)
Figure 4
. An external reference at 2.55V
at Pin 3, and the voltage at the
100k
1M
10M 100M
14031 F04
1.25V
Figure 5 shows the ideal input/output characteristics for
the LTC1403-1/LTC1403A-1. The code transitions occur
midway between successive integer LSB values (i.e.,
0.5LSB, 1.5LSB, 2.5LSB, FS – 1.5LSB). The output code
is 2’s complement with 1LSB = 2.5V/16384 = 153µV for
the LTC1403A-1, and 1LSB = 2.5V/4096 = 610µV for the
LTC1403-1. The LTC1403A-1 has 1LSB RMS of random
white noise. Figure 6a shows the LTC1819 converting a
single ended input signal to differential input signals for
optimum THD and SFDR performance as shown in the
FFT plot (Figure 6b).
Figure 6a. The LT1819 Driving the LTC1403A-1 Differentially
MAX
V
P-P
IN
011...111
011...110
011...101
100...010
100...001
100...000
LTC1403-1/LTC1403A-1
499
R4
–FS
LTC1403-1/LTC1403A-1 Transfer
499
–
1/2 LT1819
+
R3
–
1/2 LT1819
+
U1
U2
–5V
5V
Characteristic
INPUT VOLTAGE (V)
0.1µF
0.1µF
C5
C6
Figure 5
1µF
1µF
C3
C4
R5
1k
R6
1k
51
51
R1
R2
1.5V
FS – 1LSB
CM
14031 F05
C1
47pF TO
1000pF
C2
47pF TO
1000pF
1
A
A
LTC1403A-1
IN
IN
13
+
–
1403A F06a
14031fc