LTC2376-20 20-Bit, 250ksps, Low Power SAR ADC with 0.5ppm INL

30 Pages·2016·1.02 MB·English

LTC2376-20
20-Bit, 250ksps, Low Power
SAR ADC with 0.5ppm INL
FeaTures DescripTion
n 250ksps Throughput Rate The LTC®2376-20 is a low noise, low power, high speed
n ±0.5ppm INL (Typ) 20-bit successive approximation register (SAR) ADC. Op-
n Guaranteed 20-Bit No Missing Codes erating from a 2.5V supply, the LTC2376-20 has a ±V
REF
n Low Power: 5.3mW at 250ksps, 5.3µW at 250sps fully differential input range with V ranging from 2.5V
REF
n 104dB SNR (Typ) at f = 2kHz to 5.1V. The LTC2376-20 consumes only 5.3mW and
IN
n –125dB THD (Typ) at f = 2kHz achieves ±2ppm INL maximum, no missing codes at 20
IN
n Digital Gain Compression (DGC) bits with 104dB SNR.
n Guaranteed Operation to 85°C
The LTC2376-20 has a high speed SPI-compatible serial
n 2.5V Supply interface that supports 1.8V, 2.5V, 3.3V and 5V logic
n Fully Differential Input Range ±VREF while also featuring a daisy-chain mode. The fast 250ksps
n VREF Input Range from 2.5V to 5.1V throughput with no cycle latency makes the LTC2376-20
n No Pipeline Delay, No Cycle Latency ideally suited for a wide variety of high speed applications.
n 1.8V to 5V I/O Voltages An internal oscillator sets the conversion time, easing exter-
n SPI-Compatible Serial I/O with Daisy-Chain Mode nal timing considerations. The LTC2376-20 automatically
n Internal Conversion Clock powers down between conversions, leading to reduced
n 16-Lead MSOP and 4mm × 3mm DFN Packages power dissipation that scales with the sampling rate.
applicaTions The LTC2376-20 features a unique digital gain compres-
sion (DGC) function, which eliminates the driver amplifier’s
n Medical Imaging
negative supply while preserving the full resolution of the
n High Speed Data Acquisition
ADC. When enabled, the ADC performs a digital scaling
n Portable or Compact Instrumentation
function that maps zero-scale code from 0V to 0.1 • V
REF
n Industrial Process Control
and full-scale code from V to 0.9 • V . For a typical
REF REF
n Low Power Battery-Operated Instrumentation
reference voltage of 5V, the full-scale input range is now
n ATE
0.5V to 4.5V, which provides adequate headroom for
L, LT, LTC, LTM, Linear Technology and the Linear logo are registered trademarks and powering the driving amplifier from a single 5.5V supply.
SoftSpan is a trademark of Linear Technology Corporation. All other trademarks are the
property of their respective owners. Patents Pending. Protected by U.S. Patents, including
7705765, 7961132, 8319673.
Typical applicaTion
Integral Nonlinearity vs Output Code
2.5V 1.8V TO 5V 2.0
1.5
10µF 0.1µF
1.0
VVRR00EEVVFF –+ 1100ΩΩ 663883000000pppFFF IINN+– LTCRRV2EED3FFD76-20OGVNDDD RRCEBDSCSHFULDNC/A/SDSOKVIYGNDCI VSRAEMFPLE CLOCK INL ERROR (ppm) ––001...5050
2.5V TO 5.1V 237620 TA01
–1.5
47µF
(X7R, 1210 SIZE) –2.0
–524288 –262144 0 262144 524288
OUTPUT CODE
237620 TA02
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LTC2376-20
absoluTe MaxiMuM raTings
(Notes 1, 2)
Supply Voltage (V ) ...............................................2.8V Digital Output Voltage
DD
Supply Voltage (OV ) ................................................6V (Note 3) ..........................(GND – 0.3V) to (OV + 0.3V)
DD DD
Reference Input (REF) .................................................6V Power Dissipation ..............................................500mW
Analog Input Voltage (Note 3) Operating Temperature Range
IN+, IN– .........................(GND – 0.3V) to (REF + 0.3V) LTC2376C ................................................0°C to 70°C
REF/DGC Input (Note 3) ....(GND – 0.3V) to (REF + 0.3V) LTC2376I .............................................–40°C to 85°C
Digital Input Voltage Storage Temperature Range ..................–65°C to 150°C
(Note 3) ..........................(GND – 0.3V) to (OV + 0.3V)
DD
pin conFiguraTion
TOP VIEW
CHAIN 1 16 GND
TOP VIEW
VDD 2 15 OVDD CHAIN 1 16 GND
GND 3 14 SDO VDD 2 15 OVDD
IN+ 4 17 13 SCK GND 3 14 SDO
IN– 5 GND 12 RDL/SDI IINN+– 45 1132 SRCDKL/SDI
GND 6 11 BUSY GND 6 11 BUSY
REF 7 10 GND REF 7 10 GND
REF/DGC 8 9 CNV
REF/DGC 8 9 CNV
MS PACKAGE
DE PACKAGE 16-LEAD PLASTIC MSOP
16-LEAD (4mm × 3mm) PLASTIC DFN TJMAX = 150°C, θJA = 110°C/W
TJMAX = 150°C, θJA = 40°C/W
EXPOSED PAD (PIN 17) IS GND, MUST BE SOLDERED TO PCB
orDer inForMaTion
http://www.linear.com/product/LTC2376-20#orderinfo
LEAD FREE FINISH TAPE AND REEL PART MARKING* PACKAGE DESCRIPTION TEMPERATURE RANGE
LTC2376CMS-20#PBF LTC2376CMS-20#TRPBF 237620 16-Lead Plastic MSOP 0°C to 70°C
LTC2376IMS-20#PBF LTC2376IMS-20#TRPBF 237620 16-Lead Plastic MSOP –40°C to 85°C
LTC2376CDE-20#PBF LTC2376CDE-20#TRPBF 23760 16-Lead (4mm × 3mm) Plastic DFN 0°C to 70°C
LTC2376IDE-20#PBF LTC2376IDE-20#TRPBF 23760 16-Lead (4mm × 3mm) Plastic DFN –40°C to 85°C
Consult LTC Marketing for parts specified with wider operating temperature ranges. *The temperature grade is identified by a label on the shipping container.
For more information on lead free part marking, go to: http://www.linear.com/leadfree/
For more information on tape and reel specifications, go to: http://www.linear.com/tapeandreel/. Some packages are available in 500 unit reels through
designated sales channels with #TRMPBF suffix.
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LTC2376-20
elecTrical characTerisTics
The l denotes the specifications which apply over the full operating
temperature range, otherwise specifications are at T = 25°C. (Note 4)
A
SYMBOL PARAMETER CONDITIONS MIN TYP MAX UNITS
V + Absolute Input Range (IN+) (Note 5) l –0.1 V + 0.1 V
IN REF
V – Absolute Input Range (IN–) (Note 5) l –0.1 V + 0.1 V
IN REF
V + – V – Input Differential Voltage Range V = V + – V – l –V +V V
IN IN IN IN IN REF REF
V Common-Mode Input Range l V /2– V /2 V /2+ V
CM REF REF REF
0.1 0.1
I Analog Input Leakage Current 0.01 µA
IN
C Analog Input Capacitance Sample Mode 45 pF
IN
Hold Mode 5 pF
CMRR Input Common Mode Rejection Ratio f = 125kHz 86 dB
IN
converTer characTerisTics
The l denotes the specifications which apply over the full operating
temperature range, otherwise specifications are at T = 25°C. (Note 4)
A
SYMBOL PARAMETER CONDITIONS MIN TYP MAX UNITS
Resolution l 20 Bits
No Missing Codes l 20 Bits
Transition Noise 2.3 ppm
RMS
INL Integral Linearity Error (Note 6) l –2 ±0.5 2 ppm
REF/DGC = GND, (Note 6) l –2 ±0.5 2 ppm
DNL Differential Linearity Error (Note 10) l –0.5 ±0.2 0.5 ppm
BZE Bipolar Zero-Scale Error (Note 7) l –13 0 13 ppm
Bipolar Zero-Scale Error Drift ±7 ppb/°C
FSE Bipolar Full-Scale Error (Note 7) l –100 ±10 100 ppm
Bipolar Full-Scale Error Drift ±0.05 ppm/°C
DynaMic accuracy
The l denotes the specifications which apply over the full operating temperature range,
otherwise specifications are at T = 25°C and A = –1dBFS. (Notes 4, 8)
A IN
SYMBOL PARAMETER CONDITIONS MIN TYP MAX UNITS
SINAD Signal-to-(Noise + Distortion) Ratio f = 2kHz, V = 5V l 101 104 dB
IN REF
SNR Signal-to-Noise Ratio f = 2kHz, V = 5V l 101 104 dB
IN REF
f = 2kHz, V = 5V, REF/DGC = GND l 99 102 dB
IN REF
f = 2kHz, V = 2.5V l 95.5 98 dB
IN REF
THD Total Harmonic Distortion f = 2kHz, V = 5V l –125 –115 dB
IN REF
f = 2kHz, V = 5V, REF/DGC = GND l –125 –114 dB
IN REF
f = 2kHz, V = 2.5V l –123 –113 dB
IN REF
SFDR Spurious Free Dynamic Range f = 2kHz, V = 5V l 115 128 dB
IN REF
–3dB Input Bandwidth 34 MHz
Aperture Delay 500 ps
Aperture Jitter 4 ps
Transient Response Full-Scale Step 1 µs
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LTC2376-20
reFerence inpuT
The l denotes the specifications which apply over the full operating temperature range, otherwise
specifications are at T = 25°C. (Note 4)
A
SYMBOL PARAMETER CONDITIONS MIN TYP MAX UNITS
V Reference Voltage (Note 5) l 2.5 5.1 V
REF
I Reference Input Current (Note 9) l 0.24 0.3 mA
REF
V High Level Input Voltage REF/DGC Pin l 0.8V V
IHDGC REF
V Low Level Input Voltage REF/DGC Pin l 0.2V V
ILDGC REF
DigiTal inpuTs anD DigiTal ouTpuTs
The l denotes the specifications which apply over the
full operating temperature range, otherwise specifications are at T = 25°C. (Note 4)
A
SYMBOL PARAMETER CONDITIONS MIN TYP MAX UNITS
V High Level Input Voltage l 0.8 • OV V
IH DD
V Low Level Input Voltage l 0.2 • OV V
IL DD
I Digital Input Current V = 0V to OV l –10 10 µA
IN IN DD
C Digital Input Capacitance 5 pF
IN
V High Level Output Voltage I = –500µA l OV –0.2 V
OH O DD
V Low Level Output Voltage I = 500µA l 0.2 V
OL O
I Hi-Z Output Leakage Current V = 0V to OV l –10 10 µA
OZ OUT DD
I Output Source Current V = 0V –10 mA
SOURCE OUT
I Output Sink Current V = OV 10 mA
SINK OUT DD
power requireMenTs
The l denotes the specifications which apply over the full operating temperature
range, otherwise specifications are at T = 25°C. (Note 4)
A
SYMBOL PARAMETER CONDITIONS MIN TYP MAX UNITS
V Supply Voltage l 2.375 2.5 2.625 V
DD
OV Supply Voltage l 1.71 5.25 V
DD
I Supply Current 250ksps Sample Rate l 2.1 2.5 mA
VDD
I Supply Current 250ksps Sample Rate (C = 20pF) 0.1 mA
OVDD L
I Power Down Mode Conversion Done (I + I + I ) l 1 90 µA
PD VDD OVDD REF
P Power Dissipation 250ksps Sample Rate 5.25 6.25 mW
D
Power Down Mode Conversion Done (I + I + I ) 2.5 225 µW
VDD OVDD REF
aDc TiMing characTerisTics
The l denotes the specifications which apply over the full operating
temperature range, otherwise specifications are at T = 25°C. (Note 4)
A
SYMBOL PARAMETER CONDITIONS MIN TYP MAX UNITS
f Maximum Sampling Frequency l 250 ksps
SMPL
t Conversion Time l 2 3 µs
CONV
t Acquisition Time t = t – t (Note 10) l 3.312 µs
ACQ ACQ CYC HOLD
t Maximum Time Between Acquisitions l 688 ns
HOLD
t Time Between Conversions l 4 µs
CYC
t CNV High Time l 20 ns
CNVH
t CNV↑ to BUSY Delay C = 20pF l 13 ns
BUSYLH L
t Minimum Low Time for CNV (Note 11) l 20 ns
CNVL
t SCK Quiet Time from CNV↑ (Note 10) l 20 ns
QUIET
t SCK Period (Notes 11, 12) l 10 ns
SCK
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LTC2376-20
aDc TiMing characTerisTics
The l denotes the specifications which apply over the full operating
temperature range, otherwise specifications are at T = 25°C. (Note 4)
A
SYMBOL PARAMETER CONDITIONS MIN TYP MAX UNITS
t SCK High Time l 4 ns
SCKH
t SCK Low Time l 4 ns
SCKL
t SDI Setup Time From SCK↑ (Note 11) l 4 ns
SSDISCK
t SDI Hold Time From SCK↑ (Note 11) l 1 ns
HSDISCK
t SCK Period in Chain Mode t = t + t (Note 11) l 13.5 ns
SCKCH SCKCH SSDISCK DSDO
t SDO Data Valid Delay from SCK↑ C = 20pF, OV = 5.25V l 7.5 ns
DSDO L DD
C = 20pF, OV = 2.5V l 8 ns
L DD
C = 20pF, OV = 1.71V l 9.5 ns
L DD
t SDO Data Remains Valid Delay from SCK↑ C = 20pF (Note 10) l 1 ns
HSDO L
t SDO Data Valid Delay from BUSY↑ C = 20pF (Note 10) l 5 ns
DSDOBUSYL L
t Bus Enable Time After RDL↑ (Note 11) l 16 ns
EN
t Bus Relinquish Time After RDL↑ (Note 11) l 13 ns
DIS
Note 1: Stresses beyond those listed under Absolute Maximum Ratings Note 7: Bipolar zero-scale error is the offset voltage measured from
may cause permanent damage to the device. Exposure to any Absolute –0.5LSB when the output code flickers between 0000 0000 0000 0000 0000
Maximum Rating condition for extended periods may effect device and 1111 1111 1111 1111 1111. Full-scale bipolar error is the worst-case
reliability and lifetime. of –FS or +FS untrimmed deviation from ideal first and last code transitions
Note 2: All voltage values are with respect to ground. and includes the effect of offset error.
Note 3: When these pin voltages are taken below ground or above REF or Note 8: All specifications in dB are referred to a full-scale ±5V input with a
OV , they will be clamped by internal diodes. This product can handle 5V reference voltage.
DD
input currents up to 100mA below ground or above REF or OV without Note 9: f = 250kHz, I varies proportionately with sample rate.
DD SMPL REF
latch-up. Note 10: Guaranteed by design, not subject to test.
Note 4: VDD = 2.5V, OVDD = 2.5V, REF = 5V, VCM = 2.5V, fSMPL = 250kHz, Note 11: Parameter tested and guaranteed at OVDD = 1.71V, OVDD = 2.5V
REF/DGC = VREF. and OVDD = 5.25V.
Note 5: Recommended operating conditions. Note 12: t of 10ns maximum allows a shift clock frequency up to
SCK
Note 6: Integral nonlinearity is defined as the deviation of a code from a 100MHz for rising capture.
straight line passing through the actual endpoints of the transfer curve.
The deviation is measured from the center of the quantization band.
0.8*OVDD tWIDTH
0.2*OVDD
tDELAY tDELAY 50% 50%
0.8*OVDD 0.8*OVDD 237620 F01
0.2*OVDD 0.2*OVDD
Figure 1. Voltage Levels for Timing Specifications
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LTC2376-20
Typical perForMance characTerisTics
T = 25°C, V = 2.5V, OV = 2.5V, V = 2.5V,
A DD DD CM
REF = 5V, f = 250ksps, unless otherwise noted.
SMPL
Integral Nonlinearity Differential Nonlinearity
vs Output Code vs Output Code DC Histogram
2.0 0.5 50000
σ = 2.3
0.4 45000
1.5
0.3 40000
1.0
m) m) 0.2 35000
INL ERROR (pp –00..505 DNL ERROR (pp––0000....1021 COUNTS 23210055000000000000
–1.0
–0.3 10000
–1.5 –0.4 5000
–2.0 –0.5 0
–524288 –262144 0 262144 524288 –524288 –262144 0 262144 524288 –9–8–7–6–5–4–3–2–1 0 1 2 3 4 5 6 78
OUTPUT CODE OUTPUT CODE OUTPUT CODE
237620 G01 237620 G02 237620 G03
128k Point FFT f = 250ksps, THD, Harmonics
S
f = 2kHz SNR, SINAD vs Input Frequency vs Input Frequency
IN
0 108 –90
SNR = 104dB THD
–20 THD = –128dB 106 –95 2ND
SINAD = 104dB 3RD
–40 SFDR = 132dB 104 SNR S)–100
AMPLITUDE (dBFS)––––1168020000 SNR, SINAD (dBFS) 11900802 SINAD RMONICS, THD (dBF–––––111112121000555
–140 96 HA
–130
–160 94 –135
–180 92 –140
0 25 50 75 100 125 0 25 50 75 100 125 0 25 50 75 100 125
FREQUENCY (kHz) FREQUENCY (kHz) FREQUENCY (kHz)
237620 G04 237620 G05 237620 G06
SNR, SINAD vs Input Level, SNR, SINAD vs Reference THD, Harmonics vs Reference
f = 2kHz Voltage, f = 2kHz Voltage, f = 2kHz
IN IN IN
105.0 105 –110
104
–115
103
104.5 S)
dBFS) SNR dBFS)110021 SNR SINAD D (dBF –120 3TRHDD
D ( SINAD D ( TH
R, SINA104.0 R, SINA19090 ONICS, –125
N N M –130
S S 98 R
103.5 HA
97
–135
96 2ND
103.0 95 –140
–40 –30 –20 –10 0 2.5 3.0 3.5 4.0 4.5 5.0 2.5 3.0 3.5 4.0 4.5 5.0
INPUT LEVEL (dB) REFERENCE VOLTAGE (V) REFERENCE VOLTAGE (V)
237620 G07 237620 G08 237620 G09
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LTC2376-20
Typical perForMance characTerisTics
T = 25°C, V = 2.5V, OV = 2.5V, V = 2.5V,
A DD DD CM
REF = 5V, f = 250ksps, unless otherwise noted.
SMPL
SNR, SINAD vs Temperature, THD, Harmonics vs Temperature,
f = 2kHz f = 2kHz INL vs Temperature
IN IN
106 –120 2.0
1.5
105
SNR S) –125 1.0 MAX INL
F
NR, SINAD (dBFS) 111000243 SINAD MONICS, THD (dB –130 3RD THD NL ERROR (ppm)–00..505 MIN INL
S R I
HA –135 2ND –1.0
101
–1.5
100 –140 –2.0
–55 –35 –15 5 25 45 65 85 105 125 –55 –35 –15 5 25 45 65 85 105 125 –55 –35 –15 5 25 45 65 85 105 125
TEMPERATURE (°C) TEMPERATURE (°C) TEMPERATURE (°C)
237620 G10 237620 G11 237620 G12
Full-Scale Error vs Temperature Offset Error vs Temperature Supply Current vs Temperature
20 4 2.5
15 3 IVDD
ULL-SCALE ERROR (ppm)–11–00505 +–FFSS OFFSET ERROR (ppm) ––20121 WER SUPPLY CURRENT (mA) 211...005
F O 0.5
–15 –3 P IREF
IOVDD
–20 –4 0
–55 –35 –15 5 25 45 65 85 105 125 –55 –35 –15 5 25 45 65 85 105 125 –55 –35 –15 5 25 45 65 85 105 125
TEMPERATURE (°C) TEMPERATURE (°C) TEMPERATURE (°C)
237620 G13 237620 G14 237620 G15
Reference Current
Shutdown Current vs Temperature CMRR vs Input Frequency vs Reference Voltage
45 100 0.3
IVDD + IOVDD + IREF
40
95
µA) 35 A)
RRENT ( 30 B) 90 RENT (m 0.2
R-DOWN CU 122505 CMRR (d 8850 RENCE CUR 0.1
OWE 10 REFE
P 75
5
0 70 0
–50 –25 0 25 50 75 100 125 0 25 50 75 100 125 2.5 3.0 3.5 4.0 4.5 5.0
TEMPERATURE (°C) FREQUENCY (kHz) REFERENCE VOLTAGE (V)
237620 G16 237620 G17 237620 G18
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LTC2376-20
pin FuncTions
CHAIN (Pin 1): Chain Mode Selector Pin. When low, the BUSY (Pin 11): BUSY Indicator. Goes high at the start of
LTC2376-20 operates in normal mode and the RDL/SDI a new conversion and returns low when the conversion
input pin functions to enable or disable SDO. When high, has finished. Logic levels are determined by OV .
DD
the LTC2376-20 operates in chain mode and the RDL/SDI
RDL/SDI (Pin 12): When CHAIN is low, the part is in nor-
pin functions as SDI, the daisy-chain serial data input.
mal mode and the pin is treated as a bus enabling input.
Logic levels are determined by OV .
DD When CHAIN is high, the part is in chain mode and the
V (Pin 2): 2.5V Power Supply. The range of V is pin is treated as a serial data input pin where data from
DD DD
2.375V to 2.625V. Bypass V to GND with a 10µF ceramic another ADC in the daisy chain is input. Logic levels are
DD
capacitor. determined by OV .
DD
GND (Pins 3, 6, 10 and 16): Ground. SCK (Pin 13): Serial Data Clock Input. When SDO is enabled,
the conversion result or daisy-chain data from another
IN+, IN– (Pins 4, 5): Positive and Negative Differential
ADC is shifted out on the rising edges of this clock MSB
Analog Inputs.
first. Logic levels are determined by OV .
DD
REF (Pin 7): Reference Input. The range of REF is 2.5V
SDO (Pin 14): Serial Data Output. The conversion result or
to 5.1V. This pin is referred to the GND pin and should be
daisy-chain data is output on this pin on each rising edge
decoupled closely to the pin with a 47µF ceramic capacitor
of SCK MSB first. The output data is in 2’s complement
(X7R, 1210 size, 10V Rating).
format. Logic levels are determined by OV .
DD
REF/DGC (Pin 8): When tied to REF, digital gain compres-
OV (Pin 15): I/O Interface Digital Power. The range of
sion is disabled and the LTC2376-20 defines full-scale ac- DD
OV is 1.71V to 5.25V. This supply is nominally set to
cording to the ±V analog input range. When tied to GND, DD
REF
the same supply as the host interface (1.8V, 2.5V, 3.3V,
digital gain compression is enabled and the LTC2376-20
or 5V). Bypass OV to GND with a 0.1µF capacitor.
defines full-scale with inputs that swing between 10% and DD
90% of the ±V analog input range. GND (Exposed Pad Pin 17 – DFN Package Only): Ground.
REF
Exposed pad must be soldered directly to the ground plane.
CNV (Pin 9): Convert Input. A rising edge on this input
powers up the part and initiates a new conversion. Logic
levels are determined by OV .
DD
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LTC2376-20
FuncTional block DiagraM
VDD = 2.5V
REF = 2.5V TO 5.1V OVDD = 1.8V TO 5V
CHAIN
IN+ + SDO
SPI RDL/SDI
20-BIT SAMPLING ADC PORT
SCK
IN– –
CNV
BUSY
CONTROL LOGIC
REF/DGC
GND
237620 BD01
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LTC2376-20
TiMing DiagraM
Conversion Timing Using the Serial Interface
CHAIN, RDL/SDI = 0
CNV
CONVERT POWER-DOWN
BUSY
HOLD ACQUIRE
SCK
D19D18D17 D2 D1 D0
SDO
237620 TD01
applicaTions inForMaTion
OVERVIEW CONVERTER OPERATION
The LTC2376-20 is a low noise, low power, high speed The LTC2376-20 operates in two phases. During the ac-
20-bit successive approximation register (SAR) ADC. quisition phase, the charge redistribution capacitor D/A
Operating from a single 2.5V supply, the LTC2376-20 converter (CDAC) is connected to the IN+ and IN– pins
supports a large and flexible ±V fully differential input to sample the differential analog input voltage. A rising
REF
range with V ranging from 2.5V to 5.1V, making it ideal edge on the CNV pin initiates a conversion. During the
REF
for high performance applications which require a wide conversion phase, the 20-bit CDAC is sequenced through a
dynamic range. The LTC2376-20 achieves ±2ppm INL successive approximation algorithm, effectively comparing
maximum, no missing codes at 20 bits and 104dB SNR. the sampled input with binary-weighted fractions of the
reference voltage (e.g. V /2, V /4 … V /1048576)
Fast 250ksps throughput with no cycle latency makes REF REF REF
using the differential comparator. At the end of conversion,
the LTC2376-20 ideally suited for a wide variety of high
the CDAC output approximates the sampled analog input.
speed applications. An internal oscillator sets the con-
The ADC control logic then prepares the 20-bit digital
version time, easing external timing considerations. The
output code for serial transfer.
LTC2376-20 dissipates only 5.3mW at 250ksps, while an
auto power-down feature is provided to further reduce
power dissipation during inactive periods. TRANSFER FUNCTION
The LTC2376-20 features a unique digital gain compres- The LTC2376-20 digitizes the full-scale voltage of 2 × REF
sion (DGC) function, which eliminates the driver amplifier’s into 220 levels, resulting in an LSB size of 9.5µV with
negative supply while preserving the full resolution of the REF = 5V. Note that 1 LSB at 20 bits is approximately
ADC. When enabled, the ADC performs a digital scaling 1ppm. The ideal transfer function is shown in Figure 2.
function that maps zero-scale code from 0V to 0.1 • V The output data is in 2’s complement format.
REF
and full-scale code from V to 0.9 • V . For a typical
REF REF
reference voltage of 5V, the full-scale input range is now ANALOG INPUT
0.5V to 4.5V, which provides adequate headroom for
The analog inputs of the LTC2376-20 are fully differential
powering the driving amplifier from a single 5.5V supply.
in order to maximize the signal swing that can be digitized.
The analog inputs can be modeled by the equivalent circuit
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