Datasheet

LTC2380-16
10
238016fa
OVERVIEW
The LTC2380-16 is a low noise, low power, high speed 16-bit
successive approximation register (SAR) ADC. Operating
from a single 2.5V supply, the LTC2380-16 supports a
large and flexible ±V
REF
fully differential input range with
V
REF
ranging from 2.5V to 5.1V, making it ideal for high
performance applications which require a wide dynamic
range. The LTC2380-16 achieves ±0.6LSB INL max, no
missing codes at 16 bits and 96.2dB SNR.
Fast 2Msps throughput with no cycle latency makes the
LTC2380-16 ideally suited for a wide variety of high speed
applications. An internal oscillator sets the conversion time,
easing external timing considerations. The LTC2380-16
dissipates only 19mW at 2Msps, while an auto power-down
feature is provided to further reduce power dissipation
during inactive periods.
The LTC2380-16 features a unique digital gain compres-
sion (DGC) function, which eliminates the driver amplifier’s
negative supply while preserving the full resolution of the
ADC. When enabled, the ADC performs a digital scaling
function that maps zero-scale code from 0V to 0.1 • V
REF
and full-scale code from V
REF
to 0.9 • V
REF
. For a typical
reference voltage of 5V, the full-scale input range is now
0.5V to 4.5V, which provides adequate headroom for
powering the driving amplifier from a single 5.5V supply.
CONVERTER OPERATION
The LTC2380-16 operates in two phases. During the ac-
quisition phase, the charge redistribution capacitor D/A
converter (CDAC) is connected to the IN
+
and IN
–
pins
to sample the differential analog input voltage. A rising
edge on the CNV pin initiates a conversion. During the
conversion phase, the 16-bit CDAC is sequenced through a
successive approximation algorithm, effectively comparing
the sampled input with binary-weighted fractions of the
reference voltage (e.g. V
REF
/2, V
REF
/4 … V
REF
/65536) using
the differential comparator. At the end of conversion, the
CDAC output approximates the sampled analog input. The
ADC control logic then prepares the 16-bit digital output
code for serial transfer.
APPLICATIONS INFORMATION
Figure 2. LTC2380-16 Transfer Function
INPUT VOLTAGE (V)
0V
OUTPUT CODE (TWO’S COMPLEMENT)
–1
LSB
238016 F02
011...111
011...110
000...001
000...000
100...000
100...001
111...110
1
LSB
BIPOLAR
ZERO
111...111
FSR/2 – 1LSB–FSR/2
FSR = +FS – –FS
1LSB = FSR/65536
TRANSFER FUNCTION
The LTC2380-16 digitizes the full-scale voltage of 2 × REF
into 2
16
levels, resulting in an LSB size of 152µV with
REF = 5V. The ideal transfer function is shown in Figure 2.
The output data is in 2’s complement format.
R
ON
40
C
IN
45pF
R
ON
40
REF
REF
C
IN
45pF
IN
+
IN
–
BIAS
VOLTAGE
238016 F03
Figure 3. The Equivalent Circuit for the
Differential Analog Input of the LTC2380-16
ANALOG INPUT
The analog inputs of the LTC2380-16 are fully differential
in order to maximize the signal swing that can be digitized.
The analog inputs can be modeled by the equivalent circuit
shown in Figure 3. The diodes at the input provide ESD
protection. In the acquisition phase, each input sees ap-
proximately 45pF (C
IN
) from the sampling CDAC in series
with 40Ω (R
ON
) from the on-resistance of the sampling
switch. Any unwanted signal that is common to both
inputs will be reduced by the common mode rejection of
the ADC. The inputs draw a current spike while charging
the C
IN
capacitors during acquisition. During conversion,
the analog inputs draw only a small leakage current.