LTC1403-1 LINER [Linear Technology], LTC1403-1 Datasheet - Page 12

• Manufacturer Part Number: LTC1403-1
• Description: Serial 12-Bit/14-Bit, 2.8Msps Sampling ADCs with Shutdown
• Manufacturer: LINER [Linear Technology]

APPLICATIO S I FOR ATIO
LTC1403-1/LTC1403A-1
reference. The recommended range for an external refer-
ence is 2.55V to V
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
reference 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
A
the inputs. The common mode rejection holds up at
extremely high frequencies, see Figure 4. The only require-
ment is that both inputs not go below ground or exceed
V
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.
12
DD
IN
DD
+
. The ADC will always convert the bipolar difference of
. Integral nonlinearity errors (INL) and differential
– A
IN
–100
–120
–
–20
–40
–60
–80
, independent of the common mode voltage at
0
100
1k
DD
U
CMRR vs Frequency
. An external reference at 2.55V will
10k
FREQUENCY (Hz)
Figure 4
REF
U
100k
at Pin 3, and the voltage at the
1M
W
10M 100M
14031 F04
U
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 natural binary with 1LSB = 2.5V/16384 = 153 V for the
LTC1403A-1, and 1LSB = 2.5V/4096 = 610 V 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).
1.25V
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
499
R4
–FS
LTC1403-1/LTC1403A-1 Transfer
499
–
1/2 LT1819
–
1/2 LT1819
+
R3
+
U1
U2
–5V
INPUT VOLTAGE (V)
5V
Characteristic
0.1 F
0.1 F
C5
C6
Figure 5
1 F
1 F
C3
C4
R5
1k
R6
1k
51
51
R1
R2
1.5V
FS – 1LSB
14031 F05
CM
C1
47pF TO
1000pF
C2
47pF TO
1000pF
1
A
A
LTC1403A-1
IN
IN
+
–
1403A F06a
14031f