LTC2355-12_09 LINER [Linear Technology], LTC2355-12_09 Datasheet - Page 12

• Manufacturer Part Number: LTC2355-12_09
• Description: Serial 12-Bit/14-Bit, 3.5Msps Sampling ADCs with Shutdown
• Manufacturer: LINER [Linear Technology]

applications inFormation
LTC2355-12/LTC2355-14
INPUT SPAN VERSUS REFERENCE VOLTAGE
The differential input range has a 0V to V
span that equals the difference between the voltage at the
reference buffer output V
the ground (Exposed Pad Ground). The differential input
range of the ADC is 0V to 2.5V 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 LTC2355-12/LTC2355-14 has a unique differential
sample-and-hold circuit that measures input voltages from
ground to V
difference of A

–100
–120
–20
–40
–60
–80
DD
0
100
. The ADC will always convert the unipolar
IN
Figure 3. CMRR vs Frequency
+
– A
1k
IN
10k
FREQUENCY (Hz)
–
REF
, independent of the common
100k
at Pin 3, and the voltage at
1M
REF
10M 100M
unipolar voltage
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mode voltage at the inputs. The common mode rejection
holds up at extremely high frequencies, see Figure 3. The
only requirement is that both inputs not go below ground
or exceed V
ferential 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.
Figure 4 shows the ideal input/output characteristics for
the LTC2355-12/LTC2355-14. 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 straight binary with 1LSB = 2.5V/16384 = 153µV for
the LTC2355-14, and 1LSB = 2.5V/4096 = 610µV for the
LTC2355-12. The LTC2355-14 has 1LSB RMS of random
white noise.
Figure 4. LTC2355-12/LTC2355-14 Transfer Characteristic
111...111
111...110
111...101
000...010
000...001
000...000
DD
0
. Integral nonlinearity errors (INL) and dif-
INPUT VOLTAGE (V)
FS – 1LSB
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