LTC2368-24
24-Bit, 1Msps, PseudoDifferential Unipolar SAR ADC
with Integrated Digital Filter
DESCRIPTION
FEATURES
Guaranteed 24-Bits No Missing Codes
nn ±0.5ppm INL (Typ)
nn Integrated Digital Filter with Real-Time Averaging
nn Low Power: 21mW at 1Msps
nn 98dB SNR (Typ) at 1Msps
nn 140dB Dynamic Range (Typ) at 15.25sps
nn –116dB THD (Typ) at f = 2kHz
IN
nn 50Hz/60Hz Rejection
nn Guaranteed Operation to 85°C
nn Single 2.5V Supply
nn Pseudo-Differential Unipolar Input Range: 0V to V
REF
nn 1.8V to 5V SPI-Compatible Serial I/O with DaisyChain Mode
nn 16-Lead MSOP and 4mm × 3mm DFN Packages
The LTC®2368-24 is a low noise, low power, high speed
24-bit successive approximation register (SAR) ADC with
an integrated digital averaging filter. Operating from a
2.5V supply, the LTC2368-24 has a 0V to VREF pseudodifferential unipolar input range with VREF ranging from
2.5V to 5.1V. The LTC2368-24 consumes only 21mW
(Typ) and achieves ±4.5ppm INL maximum and no missing codes at 24 bits.
nn
The LTC2368-24 has an easy to use integrated digital
averaging filter that can average 1 to 65536 conversion
results real-time, dramatically improving dynamic range
from 98dB at 1Msps to 140dB at 15.25sps. No separate
programming interface or configuration register is required.
The high speed SPI-compatible serial interface supports
1.8V, 2.5V, 3.3V and 5V logic while also featuring a daisychain mode. The LTC2368-24 automatically powers down
between conversions, reducing power dissipation at lower
sampling rates.
APPLICATIONS
Seismology
Energy Exploration
nn Medical Imaging
nn High Speed Data Acquisition
nn Industrial Process Control
nn ATE
nn
nn
L, LT, LTC, LTM, Linear Technology and the Linear logo are registered trademarks and
SoftSpan is a trademark of Linear Technology Corporation. All other trademarks are the property
of their respective owners. Protected by U.S. Patents, including 7705765, 7961132, 8319673,
8810443 and Patents pending.
TYPICAL APPLICATION
Integral Nonlinearity vs Output Code
4.0
2.5V 1.8V TO 5V
3.0
VREF
0V
+
LT6202
–
10Ω
VDD
0.1µF
OVDD
IN+
3.3nF
LTC2368-24
IN–
REF
GND
CHAIN
RDL/SDI
SDO
SCK
BUSY
CNV
2.0
INL ERROR (ppm)
10µF
SAMPLE CLOCK
236824 TA01
2.5V TO 5.1V
47µF
(X7R, 1210 SIZE)
1.0
0
–1.0
–2.0
–3.0
–4.0
0
4194304
8388608 12582912 16777216
OUTPUT CODE
236824 TA01b
236824f
For more information www.linear.com/LTC2368-24
1
LTC2368-24
ABSOLUTE MAXIMUM RATINGS
(Notes 1, 2)
Supply Voltage (VDD)................................................2.8V
Supply Voltage (OVDD).................................................6V
Reference Input (REF)..................................................6V
Analog Input Voltage (Note 3)
IN+, IN–..............................(GND – 0.3V) to (REF + 0.3V)
Digital Input Voltage
(Note 3)........................... (GND – 0.3V) to (OVDD + 0.3V)
Digital Output Voltage
(Note 3)........................... (GND – 0.3V) to (OVDD + 0.3V)
Power Dissipation............................................... 500mW
Operating Temperature Range
LTC2368C................................................. 0°C to 70°C
LTC2368I..............................................–40°C to 85°C
Storage Temperature Range................... –65°C to 150°C
PIN CONFIGURATION
TOP VIEW
CHAIN
1
VDD
2
GND
3
+
4
IN–
5
GND
6
REF
7
REF
8
IN
16 GND
15 OVDD
17
GND
TOP VIEW
CHAIN
VDD
GND
IN+
IN–
GND
REF
REF
14 SDO
13 SCK
12 RDL/SDI
11 BUSY
10 GND
9 CNV
1
2
3
4
5
6
7
8
16
15
14
13
12
11
10
9
GND
OVDD
SDO
SCK
RDL/SDI
BUSY
GND
CNV
MS PACKAGE
16-LEAD PLASTIC MSOP
TJMAX = 150°C, θJA = 110°C/W
DE PACKAGE
16-LEAD (4mm × 3mm) PLASTIC DFN
TJMAX = 150°C, θJA = 40°C/W
EXPOSED PAD (PIN 17) IS GND, MUST BE SOLDERED TO PCB
ORDER INFORMATION
LEAD FREE FINISH
TAPE AND REEL
PART MARKING*
PACKAGE DESCRIPTION
TEMPERATURE RANGE
LTC2368CMS-24#PBF
LTC2368CMS-24#TRPBF
236824
16-Lead Plastic MSOP
0°C to 70°C
LTC2368IMS-24#PBF
LTC2368IMS-24#TRPBF
236824
16-Lead Plastic MSOP
–40°C to 85°C
LTC2368CDE-24#PBF
LTC2368CDE-24#TRPBF
23684
16-Lead (4mm × 3mm) Plastic DFN
0°C to 70°C
LTC2368IDE-24#PBF
LTC2368IDE-24#TRPBF
23684
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.
236824f
2
For more information www.linear.com/LTC2368-24
LTC2368-24
ELECTRICAL CHARACTERISTICS
The l denotes the specifications which apply over the full operating
temperature range, otherwise specifications are at TA = 25°C. (Note 4)
SYMBOL
PARAMETER
CONDITIONS
VIN+
Absolute Input Range (IN+)
(Note 5)
–
Absolute Input Range (IN–)
VIN+ – VIN–
Input Differential Voltage Range
IIN
Analog Input Leakage Current
CIN
Analog Input Capacitance
CMRR
Input Common Mode Rejection Ratio
VIN
MIN
TYP
MAX
UNITS
l
−0.1
VREF + 0.1
V
(Note 5)
l
−0.1
0.1
V
VIN = VIN+ – VIN–
l
0
VREF
V
0.01
μA
Sample Mode
Hold Mode
45
5
pF
pF
fIN = 500kHz
83
dB
CONVERTER CHARACTERISTICS
The l denotes the specifications which apply over the full operating
temperature range, otherwise specifications are at TA = 25°C. (Note 4)
SYMBOL
N
PARAMETER
CONDITIONS
MIN
TYP
MAX
UNITS
Resolution
l
24
Bits
No Missing Codes
l
24
Bits
Number of Averages
l
1
65536
68.5
16.8
2.24
0.87
LSBRMS
LSBRMS
LSBRMS
LSBRMS
Transition Noise
N=1
N = 16
N = 1024
N = 16384
l
l
l
l
INL
Integral Linearity Error
(Note 6)
l
–4.5
±0.5
4.5
ppm
DNL
Differential Linearity Error
(Note 7)
l
–0.9
±0.4
0.9
LSB
ZSE
Zero-Scale Error
(Note 8)
l
−20
0
20
ppm
(Note 8)
l
−100
Zero-Scale Error Drift
FSE
Full-Scale Error
±0.7
ppb/°C
±10
Full-Scale Error Drift
100
±0.05
ppm
ppm/°C
DYNAMIC ACCURACY
The l denotes the specifications which apply over the full operating temperature range,
otherwise specifications are at TA = 25°C and AIN = –1dBFS. (Notes 4, 9)
SYMBOL PARAMETER
CONDITIONS
DR
Dynamic Range
IN+ = IN– = GND, VREF = 5V, N = 1
IN+ = IN– = GND, VREF = 5V, N = 16
IN+ = IN– = GND, VREF = 5V, N = 1024
IN+ = IN– = GND, VREF = 5V, N = 16384
IN+ = IN– = GND, VREF = 5V, N = 65536
SINAD
Signal-to-(Noise + Distortion) Ratio fIN = 2kHz, VREF = 5V
Signal-to-Noise Ratio
fIN = 2kHz, VREF = 5V
fIN = 2kHz, VREF = 2.5V
fIN = 2kHz, VREF = 5V, N = 16, AIN = –20dBFS
fIN = 50Hz, VREF = 5V, N = 1024, AIN = –20dBFS
l
l
l
THD
Total Harmonic Distortion
fIN = 2kHz, VREF = 5V
fIN = 2kHz, VREF = 2.5V
fIN = 2kHz, VREF = 5V, N = 16, AIN = –20dBFS
fIN = 50Hz, VREF = 5V, N = 1024, AIN = –20dBFS
l
l
SFDR
Spurious Free Dynamic Range
fIN = 2kHz, VREF = 5V
l
SNR
–3dB Input Linear Bandwidth
MIN
TYP
MAX
UNITS
98
110
128
138
140
dB
dB
dB
dB
dB
95.5
98
dB
95.5
90
98
92.3
110
124
dB
dB
dB
dB
–116
–116
–116
–116
103
–103
–103
dB
dB
dB
dB
116
dB
34
MHz
236824f
For more information www.linear.com/LTC2368-24
3
LTC2368-24
DYNAMIC ACCURACY
The l denotes the specifications which apply over the full operating temperature range,
otherwise specifications are at TA = 25°C and AIN = –1dBFS. (Notes 4, 9)
SYMBOL PARAMETER
CONDITIONS
MIN
TYP
Aperture Delay
500
Aperture Jitter
4
Transient Response
Full–Scale Step
MAX
UNITS
ps
psRMS
312
ns
REFERENCE INPUT
The l denotes the specifications which apply over the full operating temperature range, otherwise
specifications are at TA = 25°C. (Note 4)
SYMBOL
PARAMETER
CONDITIONS
VREF
Reference Voltage
(Note 5)
l
MIN
IREF
Reference Input Current
(Note 10)
l
TYP
2.5
0.45
MAX
UNITS
5.1
V
0.6
mA
DIGITAL INPUTS AND DIGITAL OUTPUTS
The l denotes the specifications which apply over the
full operating temperature range, otherwise specifications are at TA = 25°C. (Note 4)
SYMBOL
PARAMETER
CONDITIONS
MIN
VIH
High Level Input Voltage
l
VIL
Low Level Input Voltage
l
IIN
Digital Input Current
CIN
Digital Input Capacitance
VOH
TYP
MAX
UNITS
0.8 • OVDD
VIN = 0V to OVDD
l
High Level Output Voltage
IO = –500µA
l OVDD – 0.2
V
–10
0.2 • OVDD
V
10
μA
5
pF
V
VOL
Low Level Output Voltage
IO = 500µA
l
IOZ
Hi-Z Output Leakage Current
VOUT = 0V to OVDD
l
ISOURCE
Output Source Current
VOUT = 0V
–10
mA
ISINK
Output Sink Current
VOUT = OVDD
10
mA
–10
0.2
V
10
µA
POWER REQUIREMENTS
The l denotes the specifications which apply over the full operating temperature
range, otherwise specifications are at TA = 25°C. (Note 4)
SYMBOL
PARAMETER
VDD
OVDD
IVDD
IOVDD
IPD
Supply Current
Supply Current
Power Down Mode
PD
Power Dissipation
Power Down Mode
CONDITIONS
MIN
TYP
MAX
Supply Voltage
l
2.375
2.5
2.625
V
Supply Voltage
l
1.71
5.25
V
10
l
8.4
0.4
1
90
mA
mA
μA
l
l
21
2.5
25
225
mW
μW
l
(CL = 20pF)
Conversion Done (IVDD + IOVDD + IREF)
Conversion Done (IVDD + IOVDD + IREF)
UNITS
ADC TIMING CHARACTERISTICS
The l denotes the specifications which apply over the full operating
temperature range, otherwise specifications are at TA = 25°C. (Note 4)
SYMBOL
PARAMETER
MAX
UNITS
fSMPL
Maximum Sampling Frequency
CONDITIONS
l
MIN
1
Msps
fODR
Output Data Rate
l
1
Msps
tCONV
Conversion Time
l
615
TYP
675
ns
236824f
4
For more information www.linear.com/LTC2368-24
LTC2368-24
ADC TIMING CHARACTERISTICS
The l denotes the specifications which apply over the full operating
temperature range, otherwise specifications are at TA = 25°C. (Note 4)
SYMBOL
PARAMETER
CONDITIONS
tACQ
Acquisition Time
tACQ = tCYC – tCONV – tBUSYLH (Note 7)
MIN
tCYC
TYP
MAX
UNITS
l
312
ns
Time Between Conversions
l
1
µs
l
20
ns
20
ns
tCNVH
CNV High Time
tCNVL
Minimum Low Time for CNV
(Note 11)
l
tBUSYLH
CNV↑ to BUSY↑ Delay
CL = 20pF
l
13
ns
tQUIET
SCK Quiet Time from CNV↑
(Note 7)
l
10
ns
tSCK
SCK Period
(Notes 11, 12)
l
10
ns
tSCKH
SCK High Time
l
4
ns
tSCKL
SCK Low Time
l
4
ns
tSSDISCK
SDI Setup Time From SCK↑
(Note 11)
l
4
ns
tHSDISCK
SDI Hold Time From SCK↑
(Note 11)
l
1
ns
tSCKCH
SCK Period in Chain Mode
tSCKCH = tSSDISCK + tDSDO (Note 11)
l
13.5
tDSDO
SDO Data Valid Delay from SCK↑
CL = 20pF, OVDD = 5.25V
CL = 20pF, OVDD = 2.5V
CL = 20pF, OVDD = 1.71V
l
l
l
tHSDO
SDO Data Remains Valid Delay from SCK↑ CL = 20pF (Note 7)
l
ns
7.5
8
9.5
1
ns
ns
ns
ns
tDSDOBUSYL SDO Data Valid Delay from BUSY↓
CL = 20pF (Note 7)
l
5
ns
tEN
Bus Enable Time After RDL↓
(Note 11)
l
16
ns
tDIS
Bus Relinquish Time After RDL↑
(Note 11)
l
13
ns
Note 1: Stresses beyond those listed under Absolute Maximum Ratings
may cause permanent damage to the device. Exposure to any Absolute
Maximum Rating condition for extended periods may affect device
reliability and lifetime.
Note 2: All voltage values are with respect to ground.
Note 3: When these pin voltages are taken below ground or above REF or
OVDD, they will be clamped by internal diodes. This product can handle
input currents up to 100mA below ground or above REF or OVDD without
latchup.
Note 4: VDD = 2.5V, OVDD = 2.5V, REF = 5V, fSMPL = 1MHz, N = 1.
Note 5: Recommended operating conditions.
Note 6: Integral nonlinearity is defined as the deviation of a code from a
straight line passing through the actual endpoints of the transfer curve.
The deviation is measured from the center of the quantization band.
Note 7: Guaranteed by design, not subject to test.
Note 8: Zero-scale error is the offset voltage measured from 0.5LSB when
the output code flickers between 0000 0000 0000 0000 0000 0000 and
0000 0000 0000 0000 0000 0001. Full-scale error is the deviation of the
last code transition from ideal and includes the effect of offset error.
Note 9: All specifications in dB are referred to a full-scale 5V input with a
5V reference voltage, unless otherwise specified.
Note 10: fSMPL = 1MHz, IREF varies proportionally with sample rate.
Note 11: Parameter tested and guaranteed at OVDD = 1.71V, OVDD = 2.5V
and OVDD = 5.25V.
Note 12: tSCK of 10ns maximum allows a shift clock frequency up to
100MHz for rising edge capture.
0.8 • OVDD
tWIDTH
0.2 • OVDD
tDELAY
tDELAY
0.8 • OVDD
0.8 • OVDD
0.2 • OVDD
0.2 • OVDD
50%
50%
236824 F01
Figure 1. Voltage Levels for Timing Specifications
236824f
For more information www.linear.com/LTC2368-24
5
LTC2368-24
TYPICAL PERFORMANCE CHARACTERISTICS
TA = 25°C, VDD = 2.5V, OVDD = 2.5V, REF = 5V,
fSMPL = 1Msps, N = 1, unless otherwise noted.
Integral Nonlinearity vs Output
Code
Differential Nonlinearity vs
Output Code
4.0
1.0
3.0
0.8
1.0
0
–1.0
–2.0
0.2
0.0
–0.2
–0.4
–0.8
0
4194304
8388608 12582912 16777216
OUTPUT CODE
–1.0
0
4194304
8388608 12582912 16777216
OUTPUT CODE
236824 G01
8000
8000
2000
100
200
300 400
CODE
500
600
COUNTS
4000
0
σ = 0.6
337
341
345
CODE
349
341
345
CODE
349
353
236824 G07
0
337
341
345
CODE
349
–80
–100
–120
–60
–80
–100
–120
–140
–140
–160
–160
100
200
300
FREQUENCY (kHz)
400
SNR = 110.3dB
–40
–60
0
353
128k Point FFT fSMPL = 1Msps,
fIN = 2kHz, N = 16
–20
AMPLITUDE (dBFS)
AMPLITUDE (dBFS)
337
4000
236824 G06
SNR = 98dB
THD = –116dB
SINAD = 97.9dB
SFDR = 116dB
–40
–180
700
σ = 0.87
0
333
353
128k Point FFT fSMPL = 1Msps,
fIN = 2kHz
–20
6000
0
333
600
236824 G05
DC Histogram (Near Zero Scale),
N = 65536
2000
500
2000
0
333
700
4000
300 400
CODE
6000
236824 G04
8000
200
8000
σ = 2.24
2000
0
100
DC Histogram (Near Zero Scale),
N = 16384
6000
COUNTS
COUNTS
6000
0
0
236824 G03
DC Histogram (Near Zero Scale),
N = 1024
σ = 16.8
4000
0
236824 G02
DC Histogram (Near Zero Scale),
N = 16
COUNTS
4000
2000
–0.6
–3.0
σ = 68.5
6000
0.4
COUNTS
DNL ERROR (LSB)
INL ERROR (ppm)
8000
0.6
2.0
–4.0
DC Histogram (Near Zero Scale),
N=1
500
236824 G08
–180
0
6.25
12.50
18.75
FREQUENCY (kHz)
25
31.25
236824 G09
236824f
6
For more information www.linear.com/LTC2368-24
LTC2368-24
TYPICAL PERFORMANCE CHARACTERISTICS
fSMPL = 1Msps, N = 1, unless otherwise noted.
0
32k Point FFT fSMPL = 1Msps,
fIN = 50Hz, N = 1024
–40
–60
–60
–80
–120
–140
AMPLITUDE (dBFS)
–40
–100
–80
–100
–120
–140
–80
–100
–120
–140
–160
–160
–160
–180
–180
–180
122
244
366
FREQUENCY (Hz)
–200
488
0
10
20
FREQUENCY (Hz)
SNR
THD, HARMONICS (dBFS)
1
110
97
SINAD
96
95
94
DYNAMIC RANGE
92
0.1
70k
0
10 20 30 40 50 60 70 80 90 100
FREQUENCY (kHz)
THD
2ND
–110
3RD
–120
–130
SNR, SINAD vs Input level,
fIN = 2kHz
99
0
10 20 30 40 50 60 70 80 90 100
FREQUENCY (kHz)
SNR, SINAD (dBFS)
SNR
98.0
SINAD
97.5
–110
SNR
97
SINAD
96
94
93
92
0
236824 G16
236824 G15
SNR, SINAD vs Reference
Voltage, fIN = 2kHz
98
98.5
–20
–10
INPUT LEVEL (dB)
–140
236824 G14
236824 G13
–30
–100
93
10
100
1k
10k
NUMBER OF AVERAGES (N)
97.0
–40
7.5
–90
98
SNR, SINAD (dBFS)
120
TRANSITION NOISE (LSB)
10
130
99.0
6
99
140
1
3
4.5
FREQUENCY (Hz)
THD, Harmonics vs Input
Frequency
100
100
TRANSITION NOISE
90
1.5
236824 G12
SNR, SINAD vs Input Frequency
150
0
236824 G11
Dynamic Range, Transition Noise
vs Number of Averages (N)
100
–200
30
THD, HARMONICS (dBFS)
0
DR = 140dB
–20
–60
236824 G10
DYNAMIC RANGE (dB)
0
SNR = 133dB
–40
–200
SNR, SINAD (dBFS)
8k Point FFT fSMPL = 1Msps,
IN+ = Near GND, IN– = GND,
N = 65536
32k Point FFT fSMPL = 1Msps,
fIN = 10Hz, N = 16384
–20
AMPLITUDE (dBFS)
AMPLITUDE (dBFS)
0
SNR = 124dB
–20
TA = 25°C, VDD = 2.5V, OVDD = 2.5V, REF = 5V,
91
2.5
3
3.5
4
4.5
REFERENCE VOLTAGE (V)
5
236824 G17
THD, Harmonics vs Reference
Voltage, fIN = 2kHz
–115
THD
2ND
–120
–125
3RD
–130
–135
2.5
3
3.5
4
4.5
REFERENCE VOLTAGE (V)
5
236824 G18
236824f
For more information www.linear.com/LTC2368-24
7
LTC2368-24
TYPICAL PERFORMANCE CHARACTERISTICS
fSMPL = 1Msps, N = 1, unless otherwise noted.
–110
THD, Harmonics vs Temperature,
fIN = 2kHz
SNR
THD, HARMONICS (dBFS)
SNR, SINAD (dBFS)
98.0
SINAD
97.5
97.0
96.5
96.0
–40
–15
10
35
TEMPERATURE (°C)
60
3.0
THD
–115
2.0
2ND
–120
–125
3RD
Full-Scale Error vs Temperature
–15
10
35
TEMPERATURE (°C)
60
60
10
35
TEMPERATURE (°C)
60
12
4
11
IVDD
IREF
IOVDD
10
3
2
1
0
–1
–2
–3
9
8
7
6
5
4
3
2
1
–5
–40
85
–15
10
35
TEMPERATURE (°C)
236824 G22
60
0
–40
85
–15
10
35
TEMPERATURE (°C)
60
236824 G23
Power-Down Current vs
Temperature
85
236824 G24
Reference Current vs Reference
Voltage
CMRR vs Input Frequency
10
85
Supply Current vs Temperature
5
–4
10
35
TEMPERATURE (°C)
–15
236824 G21
SUPPLY CURRENT (mA)
ZERO–SCALE ERROR (LSB)
FULL–SCALE ERROR (ppm)
–5
MIN INL
–4.0
–40
85
Zero-Scale Error vs Temperature
0
–15
–1.0
236824 G20
10
–10
–40
0
–3.0
236824 G19
5
MAX INL
1.0
–2.0
–130
–135
–40
85
INL vs Temperature
4.0
INL ERROR (PPM)
98.5
SNR, SINAD vs Temperature,
fIN = 2kHz
TA = 25°C, VDD = 2.5V, OVDD = 2.5V, REF = 5V,
100
0.6
95
0.5
REFERENCE CURRENT (mA)
8
90
6
CMRR (dB)
POWER–DOWN CURRENT (µA)
IVDD + I OVDD + I REF
4
85
80
2
0
–40
75
–15
10
35
TEMPERATURE (°C)
60
85
236824 G25
70
0.001
0.01
0.1
1
FREQUENCY (MHz)
10
236824 G26
0.4
0.3
0.2
0.1
0
2.5
3
3.5
4
4.5
REFERENCE VOLTAGE (V)
5
236824 G27
236824f
8
For more information www.linear.com/LTC2368-24
LTC2368-24
PIN FUNCTIONS
CHAIN (Pin 1): Chain Mode Selector Pin. When low, the
LTC2368-24 operates in normal mode and the RDL/SDI
input pin functions to enable or disable SDO. When high,
the LTC2368-24 operates in chain mode and the RDL/SDI
pin functions as SDI, the daisy-chain serial data input.
Logic levels are determined by OVDD.
VDD (Pin 2): 2.5V Power Supply. The range of VDD is
2.375V to 2.625V. Bypass VDD to GND with a 10µF ceramic capacitor.
GND (Pins 3, 6, 10 and 16): Ground.
IN+ (Pin 4): Analog Input. IN+ operates differential with
respect to IN– with an IN+ to IN– range of 0V to VREF.
IN– (Pin 5): Analog Ground Sense. IN– has an input range
of ±100mV with respect to GND and must be tied to the
ground plane or a remote ground sense.
REF (Pins 7, 8): Reference Input. The range of REF is 2.5V
to 5.1V. This pin is referred to the GND pin and should be
decoupled closely to the pin with a 47µF ceramic capacitor
(X7R, 1210 size, 10V rating).
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 OVDD.
BUSY (Pin 11): BUSY Indicator. Goes high at the start of
a new conversion and returns low when the conversion
has finished. Logic levels are determined by OVDD.
RDL/SDI (Pin 12): Bus Enabling Input/Serial Data Input
Pin. This pin serves two functions depending on whether
the part is operating in normal mode (CHAIN pin low) or
chain mode(CHAIN pin high). In normal mode, RDL/SDI
is a bus enabling input for the serial data I/O bus. When
RDL/SDI is low in normal mode, data is read out of the
ADC on the SDO pin. When RDL/SDI is high in normal
mode, SDO becomes Hi-Z and SCK is disabled. In chain
mode, RDL/SDI acts as a serial data input pin where data
from another ADC in the daisy chain is input. Logic levels
are determined by OVDD.
SCK (Pin 13): Serial Data Clock Input. When SDO is enabled,
the conversion result or daisy-chain data from another
ADC is shifted out on the rising edges of this clock MSB
first. Logic levels are determined by OVDD.
SDO (Pin 14): Serial Data Output. The conversion result
or daisy-chain data is output on this pin on each rising
edge of SCK MSB first. The output data is in straight binary
format. Logic levels are determined by OVDD.
OVDD (Pin 15): I/O Interface Digital Power. The range of
OVDD is 1.71V to 5.25V. This supply is nominally set to
the same supply as the host interface (1.8V, 2.5V, 3.3V,
or 5V). Bypass OVDD to GND with a 0.1µF capacitor.
GND (Exposed Pad Pin 17 – DFN Package Only): Ground.
Exposed pad must be soldered directly to the ground plane.
236824f
For more information www.linear.com/LTC2368-24
9
LTC2368-24
FUNCTIONAL BLOCK DIAGRAM
VDD = 2.5V
OVDD = 1.8V to 5V
REF = 5V
IN+
IN–
CHAIN
+
24-BIT
SAMPLING ADC
DIGITAL
FILTER
–
SPI
PORT
SDO
RDL/SDI
SCK
CNV
CONTROL LOGIC
BUSY
REF
GND
236824 BD
TIMING DIAGRAM
Conversion Timing Using the Serial Interface
CHAIN, RDL/SDI = 0
CNV
BUSY
POWER-DOWN AND ACQUIRE
CONVERT
SCK
SDO
D23 D22 D21 D20 D19 D18 D17 D16 D15 D14 D13 D12 D11 D10 D9 D8 D7 D6 D5 D4 D3 D2 D1 D0 C15 C14 C13 C12 C11 C10 C9 C8 C7 C6 C5
C4 C3 C2 C1 C0
236824 TD01
DATA FROM CONVERSION
NUMBER OF SAMPLES
AVERAGED FOR DATA
236824f
10
For more information www.linear.com/LTC2368-24
LTC2368-24
APPLICATIONS INFORMATION
OVERVIEW
The LTC2368-24 has an easy to use integrated digital
averaging filter that can average 1 to 65536 conversion
results real-time, dramatically improving dynamic range
from 98dB at 1Msps to 140dB at 15.25sps. No separate
programming interface or configuration register is required.
The high speed SPI-compatible serial interface supports
1.8V, 2.5V, 3.3V and 5V logic while also featuring a daisychain mode. The LTC2368-24 automatically powers down
between conversions, reducing power dissipation at lower
sampling rates.
CONVERTER OPERATION
The LTC2368-24 operates in two phases. During the acquisition 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 24-bit CDAC is sequenced through a
successive approximation algorithm, effectively comparing
the sampled input with binary-weighted fractions of the
reference voltage (e.g. VREF/2, VREF/4 … VREF/16777216)
using the differential comparator. At the end of conversion,
the CDAC output approximates the sampled analog input.
The ADC control logic then passes the 24-bit digital output
code to the digital filter for further processing.
1LSB = FS/16777216
111...110
111...101
OUTPUT CODE
The LTC2368-24 is a low noise, low power, high speed
24-bit successive approximation register (SAR) ADC with
an integrated digital averaging filter. Operating from a
2.5V supply, the LTC2368-24 has a 0V to VREF pseudodifferential unipolar input range with VREF ranging from
2.5V to 5.1V. The LTC2368-24 consumes only 21mW
(Typ) and achieves ±4.5ppm INL maximum and no missing codes at 24 bits.
111...111
111...100
000...011
UNIPOLAR
ZERO
000...010
000...001
000...000
0V
1
LSB
FS – 1LSB
INPUT VOLTAGE (V)
236824 F02
Figure 2. LTC2368-24 Transfer Function
ANALOG INPUT
The analog inputs of the LTC2368-24 are pseudodifferential in order to reduce any unwanted signal that
is common to both inputs. 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 approximately 45pF (CIN)
from the sampling CDAC in series with 40Ω (RON) 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 CIN capacitors during
acquisition. During conversion, the analog inputs draw
only a small leakage current.
REF
RON
40Ω
IN+
REF
IN–
TRANSFER FUNCTION
RON
40Ω
CIN
45pF
CIN
45pF
BIAS
VOLTAGE
236824 F03
The LTC2368-24 digitizes the full-scale voltage of REF into
224 levels, resulting in an LSB size of 0.3µV with REF = 5V.
The ideal transfer function is shown in Figure 2. The output
data is in straight binary format.
Figure 3. The Equivalent Circuit for the Pseudo-Differential
Unipolar Analog Input of the LTC2368-24
236824f
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11
LTC2368-24
APPLICATIONS INFORMATION
INPUT DRIVE CIRCUITS
Input Currents
A low impedance source can directly drive the high impedance inputs of the LTC2368-24 without gain error. A high
impedance source should be buffered to minimize settling
time during acquisition and to optimize ADC linearity. For
best performance, a buffer amplifier should be used to
drive the analog inputs of the LTC2368-24. The amplifier
provides low output impedance, which produces fast settling of the analog signal during the acquisition phase. It
also provides isolation between the signal source and the
ADC input currents.
One of the biggest challenges in coupling an amplifier to
the LTC2368-24 is in dealing with current spikes drawn
by the ADC inputs at the start of each acquisition phase.
The ADC inputs may be modeled as a switched capacitor
load of the drive circuit. A drive circuit may rely partially
on attenuating switched-capacitor current spikes with
small filter capacitors CFILT placed directly at the ADC
inputs, and partially on the driver amplifier having sufficient bandwidth to recover from the residual disturbance.
Amplifiers optimized for DC performance may not have
sufficient bandwidth to fully recover at the ADC’s maximum
conversion rate, which can produce nonlinearity and other
errors. Coupling filter circuits may be classified in three
broad categories:
Noise and Distortion
The noise and distortion of the buffer amplifier and signal
source must be considered since they add to the ADC noise
and distortion. Noisy input signals should be filtered prior
to the buffer amplifier input with an appropriate filter to
minimize noise. The simple 1-pole RC lowpass filter (LPF1)
shown in Figure 4 is sufficient for many applications.
LPF1
VREF
0V
50Ω
LPF2
+
66nF
LT6202
–
10Ω
IN+
LTC2368-24
3.3nF
IN–
BW = 48kHz
BW = 1.6MHz
236824 F04
Figure 4. Input Signal Chain
A coupling filter network (LPF2) should be used between
the buffer and ADC input to minimize disturbances reflected
into the buffer from sampling transients. Long RC time
constants at the analog inputs will slow down the settling
of the analog inputs. Therefore, LPF2 typically requires a
wider bandwidth than LPF1. This filter also helps minimize
the noise contribution from the buffer. A buffer amplifier
with a low noise density must be selected to minimize
degradation of the SNR.
High quality capacitors and resistors should be used in the
RC filters since these components can add distortion. NP0
and silver mica type dielectric capacitors have excellent
linearity. Carbon surface mount resistors can generate
distortion from self heating and from damage that may
occur during soldering. Metal film surface mount resistors
are much less susceptible to both problems.
Fully Settled – This case is characterized by filter time
constants and an overall settling time that is considerably shorter than the sample period. When acquisition
begins, the coupling filter is disturbed. For a typical first
order RC filter, the disturbance will look like an initial step
with an exponential decay. The amplifier will have its own
response to the disturbance, which may include ringing. If
the input settles completely (to within the accuracy of the
LTC2368-24), the disturbance will not contribute any error.
Partially Settled – In this case, the beginning of acquisition
causes a disturbance of the coupling filter, which then
begins to settle out towards the nominal input voltage.
However, acquisition ends (and the conversion begins)
before the input settles to its final value. This generally
produces a gain error, but as long as the settling is linear,
no distortion is produced. The coupling filter’s response
is affected by the amplifier’s output impedance and other
parameters. A linear settling response to fast switchedcapacitor current spikes can NOT always be assumed for
precision, low bandwidth amplifiers. The coupling filter
serves to attenuate the current spikes’ high-frequency
energy before it reaches the amplifier.
Fully Averaged – If the coupling filter capacitors (CFILT) at
the ADC inputs are much larger than the ADC’s sample
capacitors (45pF), then the sampling glitch is greatly attenuated. The driving amplifier effectively only sees the
average sampling current, which is quite small. At 1Msps,
the equivalent input resistance is approximately 22k (as
236824f
12
For more information www.linear.com/LTC2368-24
LTC2368-24
APPLICATIONS INFORMATION
shown in Figure 5), a benign resistive load for most precision amplifiers. However, resistive voltage division will
occur between the coupling filter’s DC resistance and the
ADC’s equivalent (switched-capacitor) input resistance,
thus producing a gain error.
IN+
CFILT >> 45pF
IN–
CFILT >> 45pF
REQ
BIAS
VOLTAGE
LTC2368-24
REQ
236824 F05
REQ =
1
fSMPL • 45pF
VE =
RS1 +RS2
I +I
• (IL1 –IL2 ) + (RS1 –RS2 ) • L1 L2
2
2
The common mode input leakage current, (IL1 + IL2)/2, is
typically extremely small (Figure 6) over the entire operating
temperature range and common mode input voltage range.
Thus, any reasonable mismatch (below 5%) of the source
impedances RS1 and RS2 will cause only a negligible error.
The differential input leakage current, (IL1 – IL2), increases
with temperature as shown in Figure 6 and is maximum
when VIN = VREF. The differential leakage current is also
typically very small, and its nonlinear component is even
smaller. Only the nonlinear component will impact the
ADC’s linearity.
Figure 5. Equivalent Circuit for the Pseudo-Differential
Unipolar Analog Input of the LTC2368-24 at 1Msps
The input leakage currents of the LTC2368-24 should
also be considered when designing the input drive circuit,
because source impedances will convert input leakage
currents to an added input voltage error. The input leakage
currents, both common mode and differential, are typically
extremely small over the entire operating temperature
range. Figure 6 shows input leakage currents over temperature for a typical part.
INPUT LEAKAGE (nA)
10
VIN = VREF
DIFFERENTIAL
5
0
COMMON
–5
–40
–15
10
35
TEMPERATURE (°C)
60
RS1
IL1
+
VE
–
RS2
IN+
LTC2368-24
IN–
IL2
236824 F07
Figure 7. Source Impedances and Input
Leakage Currents of the LTC2368-24
For optimal performance, it is recommended that the
source impedances, RS1 and RS2, be between 5Ω and
50Ω and with 1% tolerance. For source impedances in
this range, the voltage and temperature coefficients of
RS1 and RS2 are usually not critical. The guaranteed AC
and DC specifications are tested with 10Ω source impedances, and the specifications will gradually degrade with
increased source impedances due to incomplete settling
of the inputs.
Low Side Current Sensing
85
236824 F06
Figure 6. Common Mode and Differential
Input Leakage Current over Temperature
Let RS1 and RS2 be the source impedances of the input
drive circuit shown in Figure 7, and let IL1 and IL2 be the
leakage currents flowing out of the ADC’s analog inputs.
The voltage error, VE, due to the leakage currents can be
expressed as:
Figure 8 shows a typical low side current sense application
where a sense resistor, RSENSE, is placed in series with
the ground terminal of a circuit block to produce a voltage, VSENSE, that is amplified and buffered before being
presented to the ADC input. VSENSE is inherently unipolar
with respect to ground, making the pseudo-differential
unipolar input range of the LTC2368-24 ideally suited for
low side current sense applications.
236824f
For more information www.linear.com/LTC2368-24
13
LTC2368-24
APPLICATIONS INFORMATION
8V
LOAD
ILOAD
3
+
VSENSE
–
RSENSE = 100Ω
2
7
+
LTC2057
–
4
6
10Ω
IN+
LTC2368-24
4.7µF
IN–
–3.6V
236824 F08
0.047µF
208Ω
4.99k
Figure 8. Low Side Current Sensing
The LTC2057 is a high precision, zero drift amplifier
that complements the low offset and offset drift of the
LTC2368-24. The LTC2057 is shown in a non-inverting
amplifier configuration to provide a gain of 25 to VSENSE.
Low noise is achieved using the digital averaging filter
provided by the LTC2368-24.
DC Accuracy
The very low level of distortion is a direct consequence of
the excellent INL of the LTC2368-24, and this property can
be exploited in DC applications. Note that while the driver
amplifier in Figure 4 (LT6202) is characterized by excellent AC specifications, its DC specifications do not match
those of the LTC2368-24. The offset of this amplifier, for
example, is more than 500µV under certain conditions.
In contrast, the LTC2368-24 has a guaranteed maximum
offset error of 130µV (typical drift ±0.007ppm/°C), and a
guaranteed maximum full-scale error of 150ppm (typical
drift ±0.05ppm/°C). Low drift is important to maintain
accuracy over wide temperature range in a calibrated
system. The LTC2057 shown in Figure 8 is an example
of an amplifier with low offset and offset drift.
Amplifiers have to be selected very carefully to provide a
24-bit accurate DC signal chain. A large-signal open-loop
gain of at least 126dB may be required to ensure 1ppm
linearity for amplifiers configured for a gain of negative
1. However, less gain is sufficient if the amplifier’s gain
characteristic is known to be (mostly) linear. An amplifier’s offset versus signal level must be considered for
amplifiers configured as unity gain buffers. For example,
1ppm linearity may require that the offset is known to
vary less than 5μV for a 5V swing. However, greater offset
variations may be acceptable if the relationship is known
to be (mostly) linear. Unity-gain buffer amplifiers typically
require substantial headroom to the power supply rails for
best performance. Inverting amplifier circuits configured
to minimize swing at the amplifier input terminals may
perform better with less headroom than unity-gain buffer
amplifiers. The linearity and thermal properties of an inverting amplifier’s feedback network should be considered
carefully to ensure DC accuracy.
ADC REFERENCE
The LTC2368-24 requires an external reference to define
its input range. A low noise, low temperature drift reference is critical to achieving the full data sheet performance
of the ADC. Linear Technology offers a portfolio of high
performance references designed to meet the needs of
many applications. With its small size, low power and high
accuracy, the LTC6655-5 is particularly well suited for
use with the LTC2368-24. The LTC6655-5 offers 0.025%
(max) initial accuracy and 2ppm/°C (max) temperature
coefficient for high precision applications.
When choosing a bypass capacitor for the LTC6655-5, the
capacitor’s voltage rating, temperature rating, and package size should be carefully considered. Physically larger
capacitors with higher voltage and temperature ratings tend
to provide a larger effective capacitance, better filtering
the noise of the LTC6655-5, and consequently producing
a higher SNR. Therefore, we recommend bypassing the
LTC6655-5 with a 47μF ceramic capacitor (X7R, 1210
size, 10V rating) close to the REF pin.
236824f
14
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LTC2368-24
APPLICATIONS INFORMATION
The REF pin of the LTC2368-24 draws charge (QCONV) from
the 47µF bypass capacitor during each conversion cycle.
The reference replenishes this charge with a DC current,
IREF = QCONV/tCYC. The DC current draw of the REF pin,
IREF, depends on the sampling rate and output code. If
the LTC2368-24 is used to continuously sample a signal
at a constant rate, the LTC6655-5 will keep the deviation
of the reference voltage over the entire code span to less
than 0.5ppm.
improvement of the SNR as N increases, because any
noise on the REF pin will modulate around the fundamental
frequency of the input signal. Therefore, it is critical to
use a low-noise reference, especially if the input signal
amplitude approaches full-scale. For small input signals,
the dynamic range will improve as described earlier in
this section.
When idling, the REF pin on the LTC2368-24 draws only
a small leakage current (< 1µA). In applications where a
burst of samples is taken after idling for long periods as
shown in Figure 9, IREF quickly goes from approximately
0µA to a maximum of 1mA at 1Msps. This step in DC
current draw triggers a transient response in the reference that must be considered since any deviation in the
reference output voltage will affect the accuracy of the
output code. In applications where the transient response
of the reference is important, the fast settling LTC6655-5
reference is also recommended.
Fast Fourier Transform (FFT) techniques are used to test
the ADC’s frequency response, distortion and noise at the
rated throughput. By applying a low distortion sine wave
and analyzing the digital output using an FFT algorithm,
the ADC’s spectral content can be examined for frequencies outside the fundamental. The LTC2368-24 provides
guaranteed tested limits for both AC distortion and noise
measurements.
In applications where power management is critical, the
external reference may be powered down such that the
voltage on the REF pin can go below 2V. In such scenarios,
it is recommended that after the voltage on the REF pin
recovers to above 2V, the ADC’s internal digital I/O registers
be cleared before the initiation of the next conversion. This
can be achieved by providing at least 20 rising edges on
the SCK pin before the first CNV rising edge.
Reference Noise
The dynamic range of the ADC will increase approximately
3dB for every 2× increase in the number of conversion
results averaged (N). The SNR should also improve as a
function of N in the same manner. For large input signals
near full-scale, however, any reference noise will limit the
DYNAMIC PERFORMANCE
Dynamic Range
The dynamic range is the ratio of the RMS value of a full
scale input to the total RMS noise measured with IN+ tied
to a DC voltage near GND and IN– shorted to GND. The
dynamic range of the LTC2368-24 without averaging (N =
1) is 98dB which improves by 3dB for every 2× increase
in the number of conversion results averaged (N) per
measurement.
Signal-to-Noise and Distortion Ratio (SINAD)
The signal-to-noise and distortion ratio (SINAD) is the
ratio between the RMS amplitude of the fundamental input
frequency and the RMS amplitude of all other frequency
components at the ADC output. The output is band-limited
to frequencies from above DC and below half the sampling
frequency. Figure 10 shows that the LTC2368-24 achieves
a typical SINAD of 98dB at a 1MHz sampling rate with a
2kHz input.
CNV
IDLE
PERIOD
IDLE
PERIOD
236824 F09
Figure 9. CNV Waveform Showing Burst Sampling
236824f
For more information www.linear.com/LTC2368-24
15
LTC2368-24
APPLICATIONS INFORMATION
0
–40
AMPLITUDE (dBFS)
interface power supply (OVDD). The flexible OVDD supply
allows the LTC2368-24 to communicate with any digital
logic operating between 1.8V and 5V, including 2.5V and
3.3V systems.
SNR = 98dB
THD = –116dB
SINAD = 97.9dB
SFDR = 116dB
–20
–60
–80
Power Supply Sequencing
–100
–120
–140
–160
–180
0
100
200
300
FREQUENCY (kHz)
400
500
236824 F10
Figure 10. 128k Point FFT Plot of the LTC2368-24
with fIN = 2kHz and fSMPL = 1MHz
Signal-to-Noise Ratio (SNR)
The signal-to-noise ratio (SNR) is the ratio between the
RMS amplitude of the fundamental input frequency and
the RMS amplitude of all other frequency components
except the first five harmonics and DC. Figure 10 shows
that the LTC2368-24 achieves a typical SNR of 98dB at a
1MHz sampling rate with a 2kHz input.
Total Harmonic Distortion (THD)
Total Harmonic Distortion (THD) is the ratio of the RMS sum
of all harmonics of the input signal to the fundamental itself.
The out-of-band harmonics alias into the frequency band
between DC and half the sampling frequency (fSMPL/2).
THD is expressed as:
THD= 20log
V22 + V32 + V42 +…+ VN2
V1
where V1 is the RMS amplitude of the fundamental
frequency and V2 through VN are the amplitudes of the
second through Nth harmonics.
POWER CONSIDERATIONS
The LTC2368-24 provides two power supply pins: the
2.5V power supply (VDD), and the digital input/output
The LTC2368-24 does not have any specific power supply sequencing requirements. Care should be taken to
adhere to the maximum voltage relationships described
in the Absolute Maximum Ratings section. The LTC236824 has a power-on-reset (POR) circuit that will reset the
LTC2368-24 at initial power-up or whenever the power
supply voltage drops below 1V. Once the supply voltage
re-enters the nominal supply voltage range, the POR will
reinitialize the ADC. No conversions should be initiated
until 200µs after a POR event to ensure the re-initialization
period has ended. Any conversions initiated before this
time will produce invalid results. In addition, after a POR
event, it is recommended that the ADC’s internal digital
I/O registers be cleared before the initiation of the next
conversion. This can be achieved by providing at least 20
rising edges on the SCK pin before the first CNV rising edge.
TIMING AND CONTROL
CNV Timing
The LTC2368-24 conversion is controlled by CNV. A rising edge on CNV will start a conversion and power up
the LTC2368-24. Once a conversion has been initiated,
it cannot be restarted until the conversion is complete.
For optimum performance, CNV should be driven by a
clean low jitter signal. Converter status is indicated by the
BUSY output which remains high while the conversion is
in progress. To ensure that no errors occur in the digitized
results, any additional transitions on CNV should occur
within 40ns from the start of the conversion or after the
conversion has been completed. Once the conversion has
completed, the LTC2368-24 powers down and begins
acquiring the input signal.
236824f
16
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LTC2368-24
APPLICATIONS INFORMATION
Internal Conversion Clock
The LTC2368-24 has an internal clock that is trimmed to
achieve a maximum conversion time of 675ns. With a minimum acquisition time of 312ns, a maximum sample rate
of 1Msps is guaranteed without any external adjustments.
Auto Power-Down
The LTC2368-24 automatically powers down after a conversion has been completed and powers up once a new
conversion is initiated on the rising edge of CNV. During
power-down, data from the last conversion can be clocked
out. To minimize power dissipation during power-down,
disable SDO and turn off SCK. The auto power-down feature
will reduce the power dissipation of the LTC2368-24 as the
sampling rate is reduced. Since power is consumed only
during a conversion, the LTC2368-24 remains powereddown for a larger fraction of the conversion cycle (tCYC) at
lower sample rates, thereby reducing the average power
dissipation which scales with the sampling rate as shown
in Figure 11.
10
label2IVDD
label6
label5
label4
label3
IREF
IOVDD
SUPPLY CURRENT (mA)
8
Digital Averaging Filter (SINC1 Decimation Filter)
Many SAR ADC applications use digital averaging techniques to reduce the uncertainty of measurements due
to noise. An FPGA or DSP is typically needed to compute
the average of multiple A/D conversion results. The
LTC2368-24 features an integrated digital averaging
filter that can provide the function without any additional
hardware, thus simplifying the application solution and
providing a number of unique advantages. The digital
averaging filter can be used to average blocks of as few
as N = 1 or as many as N = 65536 conversion results.
The digital averaging filter described in this section is also
known as a SINC1 digital decimation filter. A SINC1 digital
decimation filter is an FIR filter with N equal-valued taps.
Block Diagram
Figure 12 illustrates a block diagram of the digital averaging
filter, including a Conversion Result Register, the Digital
Signal Processing (DSP) block, and an I/O Register.
6
4
The Conversion Result Register holds the 24-bit conversion
result from the most recent sample taken at the rising edge
of CNV. The DSP block provides an averaging operation,
2
0
The interface controls a digital averaging filter, which
can be used to increase the dynamic range of measurements. The flexible OVDD supply allows the LTC2368-24
to communicate with any digital logic operating between
1.8V and 5V, including 2.5V and 3.3V systems. The digital
interface of the LTC2368-24 is backwards compatible with
the LTC2378-20 family.
0
200
400
600
800
SAMPLING RATE (kHz)
1000
DIGITAL AVERAGING FILTER
236824 F11
Figure 11. Power Supply Current of the LTC2368-24
Versus Sampling Rate
DIGITAL INTERFACE
The LTC2368-24 features a simple and easy to use serial
digital interface that supports output data rates up to 1Msps.
24-BIT
SAMPLING ADC
CNV
CONVERSION
RESULT
REGISTER
DIGITAL
SIGNAL
PROCESSING
I/O
REGISTER
SDO
SCK
236824 F12
Figure 12. Block Diagram with Digital Averaging Filter
236824f
For more information www.linear.com/LTC2368-24
17
LTC2368-24
APPLICATIONS INFORMATION
loading average values of conversion results into the I/O
Register for the user to read through the serial interface.
Reducing Measurement Noise Using the Digital
Averaging Filter
Conventional SAR Operation
Digital averaging techniques are often employed to reduce the uncertainty of measurements due to noise. The
LTC2368-24 features a digital averaging filter, making it
easy to perform an averaging operation without providing
any additional hardware and software.
The LTC2368-24 may be operated like a conventional nolatency SAR as shown in Figure 13. Each conversion result
is read out via the serial interface before the next conversion
is initiated. Note how the contents of the I/O Register track
the contents of the Conversion Result Register and that
both registers contain a result corresponding to a single
conversion. The digital averaging filter is transparent to
the user when the LTC2368-24 is operated in this way. No
programming is required. Simply read out each conversion
result in each cycle. Ri represents the 24-bit conversion
result corresponding to conversion number i. As few as
20 SCKs may be given in each conversion cycle (instead
of the 24 shown in Figure 13) to obtain a 20-bit accurate
result, making the LTC2368-24 backwards compatible
with the LTC2378-20.
CONVERSION
0
NUMBER
1
2
3
Averaging 4 Conversion Results
Figure 14 shows a case where an output result is read
out once for every 4 conversions initiated. As shown, the
output result read out from the I/O Register is the average
of the 4 previous conversion results. The digital averaging
filter will automatically average conversion results until an
output result is read out. When an output result is read
out, the digital averaging filter is reset and a new averaging
operation starts with the next conversion result.
In this example, output results are read out after conversion
numbers 0, 4 and 8. The digital averaging filter is reset after
4
5
6
7
8
CNV
BUSY
CONVERSION
RESULT
REGISTER
R0
R1
R2
R3
R4
R5
R6
R7
R8
I/O
REGISTER
R0
R1
R2
R3
R4
R5
R6
R7
R8
1
24
1
24
1
24
1
24
1
24
1
24
1
24
1
24
1
24
SCK
236824 F13
Figure 13. Conventional SAR Operation Timing
236824f
18
For more information www.linear.com/LTC2368-24
LTC2368-24
APPLICATIONS INFORMATION
CONVERSION
0
NUMBER
2
1
3
4
5
6
7
8
CNV
BUSY
CONVERSION
RESULT
REGISTER
I/O
REGISTER
R0
R1
R2
R3
R4
R5
R6
R7
R8
R(–3)+R(–2)+R(–1)+R0
4
R1
R1 + R2
2
R1 + R2 + R3
4
R1 + R2 + R3 + R4
4
R5
R5 + R6
2
R5 + R6 + R7
4
R5 + R6 + R7 + R8
4
1
24
1
24
1
24
SCK
236824 F14
Figure 14. Averaging 4 Conversion Results
conversion number 0 and starts a new averaging operation
beginning with conversion number 1. The output result
(R1 + R2 + R3 + R4)/4 is read out after conversion number
4, which resets the digital averaging filter again. Since the
digital averaging filter automatically averages conversion
results for each new conversion performed, an arbitrary
number of conversion results, up to the upper limit of
65536, may be averaged with no programming required.
Averaging 3 Conversion Results
The output result, when averaging N conversion results
for values of N that are not a power of 2, will be scaled by
N/M, where M is a weighting factor that is the next power
of 2 greater than N (described later in the Weighting Factor section). Figure 15 shows an example where only 3
conversion results are averaged. The output result read
out is scaled by N/M = ¾.
Using the Digital Averaging Filter with Reduced
Data Rate
The examples given in Figures 13, 14 and 15 illustrate
some of the most common ways to use the LTC2368-24.
Simply read each individual conversion result, or read an
average of N conversion results. In each case, the result is
read out between two consecutive A/D conversion (BUSY)
periods, requiring a fast serial shift clock.
Distributed Read
A relatively slower serial shift clock may be used when
using a distributed read. Distributed reads require that
multiple conversion results be averaged.
If at least 1 but less than 20 SCK pulses(0 < SCKs < 20)
are given in a conversion cycle between 2 BUSY falling
edges (See Figure 16), the I/O Register is not updated
with the output of the digital averaging filter, preserving
its contents. This allows an output result to be read from
the I/O Register over multiple conversion cycles, easing
the speed requirements of the serial interface.
A read is initiated by a rising edge of a first SCK pulse and
it must be terminated before a next read can be initiated.
The digital averaging filter is reset upon the initiation of a
read wherein a new averaging operation begins. Conversions completed after the digital averaging filter is reset
236824f
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19
LTC2368-24
APPLICATIONS INFORMATION
CONVERSION
0
NUMBER
1
2
3
4
5
6
7
8
CNV
BUSY
CONVERSION
RESULT
REGISTER
I/O
REGISTER
R0
R1
R2
R3
R4
R5
R6
R7
R8
R(–2) + R(–1) + R0
4
R1
R1 + R2
2
R1 + R2 + R3
4
R4
R4 + R5
2
R4 + R5 + R6
4
R7
R7 + R8
2
1
24
1
24
1
24
SCK
236824 F15
Figure 15. Averaging 3 Conversion Results
will automatically be averaged until a new read is initiated.
Thus, the digital averaging filter will calculate averages of
conversion results from conversions completed between
a time when one read is initiated to when a next read is
initiated.
is terminated at the completion of conversion number
5. A second read is initiated after conversion number 5,
which results in (R2 + R3 + R4 + R5)/4 being read out from
the I/O Register since conversion numbers 2, 3, 4 and 5
completed between the initiation of the two reads shown.
A read is terminated by providing either 0 or greater
than 19 SCK pulses (rising edges) in a conversion cycle
between 2 BUSY falling edges, allowing the I/O Register
to be updated with new averages from the output of the
digital averaging filter.
Averaging 25 Conversions Using a Distributed Read
Averaging 4 Conversions Using a Distributed Read
Figure 16 shows an example where reads are initiated
every 4 conversion cycles, and the I/O register is read
over 3 conversion cycles. This allows the serial interface
to run at 1/3 of the speed that it would otherwise have to
run. The first rising SCK edge initiates a 1st read, and 3
groups of 8-bits are read out over 3 conversion cycles.
No SCK pulses are provided between the BUSY falling
edges of conversion numbers 4 and 5, whereby the read
Figure 17 shows an example where a read is initiated every
25 conversion cycles, using a single SCK pulse per conversion cycle to read the output result from the I/O Register.
The first rising SCK edge initiates a read where a single
bit is then read out over the next 23 conversion cycles. No
SCK pulses are provided between the BUSY falling edges
of conversion numbers 25 and 26, whereby the read is
terminated at the completion of conversion number 26. A
2nd read is initiated after conversion number 26, resulting
in (R2 + R3 +…+ R25 + R26)/32 being read out from the
I/O Register. Since 0 < SCKs < 20 pulses are given each
conversion period during the read, the contents of the I/O
Register are not updated, allowing the distributed read to
occur without interruption.
236824f
20
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LTC2368-24
APPLICATIONS INFORMATION
CONVERSION
0
NUMBER
1
2
3
4
5
6
7
8
CNV
CONVERSIONS COMPLETED BETWEEN
INITIATION OF READS
BUSY
CONVERSION
RESULT
REGISTER
R1
R0
R2
R3
R4
R5
R6
R8
R7
BLOCK OF CONVERSION RESULTS AVERAGED FOR 1 MEASUREMENT
I/O R(–6) +R(–5) +R(–4) +R(–3)
REGISTER
4
R(–2) + R(–1) + R0 + R1
4
1
8
9
16
17
R2 + R3 + R4 + R5
4
24
1
8
9
16
17
24
SCK
0 SCKs
0 < SCKs < 20
0 < SCKs < 20
0 < SCKs < 20
0 SCKs
0 < SCKs < 20
0 < SCKs < 20
1ST READ
0 < SCKs < 20
0 SCKs
2ND READ
READ READ
TERMINATED INITIATED
DIGITAL AVERAGING
FILTER RESETS
236824 F16
READ READ
TERMINATED INITIATED
DIGITAL AVERAGING
FILTER RESETS
Figure 16. Averaging 4 Conversion Results and Reading Out Data with a Distributed Read
CONVERSION
0
NUMBER
1
2
3
4
23
24
25
26
27
CNV
CONVERSIONS COMPLETED BETWEEN
INITIATION OF READS
BUSY
CONVERSION
RESULT
REGISTER
R1
R0
R2
I/O
REGISTER
R3
R23
R24
R25
R(–23) + R(–22) +…+ R0 + R1
(REPEATING READ PATTERN – AVERAGE OF 25 CONVERSION
32
RESULTS FROM 25 CONVERSIONS PRECEDING INITIATION OF READ)
1
2
3
4
23
24
R26
R2 + R3 +…+ R25 + R26
32
1
SCK
0 SCKs
0 < SCKs < 20
0 < SCKs < 20
0 < SCKs < 20
1 SCK/CNV
0 < SCKs < 20
0 < SCKs < 20
0 SCKs
READ
0 < SCKs < 20
236824 F17
Figure 17. Averaging 25 Conversion Results and Reading Out Data with a Distributed Read
236824f
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21
LTC2368-24
APPLICATIONS INFORMATION
Minimum Shift Clock Frequency
Table 1. Weighting Factors and Throughput for Various Values of N
Requiring at least 1 SCK pulse per conversion cycle while
performing a read sets a lower limit on the SCK frequency
that can be used which is: fSCK = fSMPL.
Noise vs Averaging
The noise of the ADC is un-correlated from one sample to
the next. As a result, the ADC noise for a measurement will
decrease by √N where N is the number of A/D conversion
results averaged for a given measurement. Other noise
sources, such as noise from the input buffer amplifier and
reference noise may be correlated from sample-to-sample
and may be reduced by averaging, but to a lesser extent.
Weighting Factor
When conversion results are averaged, the resulting
output code represents an equally weighted average of
the previous N samples if N is a power of 2. If N is not a
power of 2, a weighting factor, M, is chosen according to
Table 1. Specifically, if Ri represents the 24-bit conversion
result of the ith analog sample, then the output code, D,
representing N averaged conversion results is defined as:
N
Ri
i=1 M
D= ∑
Table 1 illustrates weighting factors for any number of
averages, N, between 1 and 65536 and the resulting
data throughputs. Note that M reaches a maximum value
of 65536 when N = 65536. For N > 65536, the digital
averaging filter will continue to accumulate conversion
results such that N/M > 1. In such a case, if the ADC core
produces conversion results that have a non-zero mean,
the output result will eventually saturate at positive or
negative full-scale.
N
M
DATA THROUGHPUT
1
1
1Msps
2
2
500ksps
3-4
4
333.3ksps - 250ksps
5-8
8
200ksps - 125ksps
9 - 16
16
111.1ksps - 62.5ksps
17 - 32
32
58.8ksps - 31.3ksps
33 - 64
64
30.3ksps - 15.6ksps
65 - 128
128
15.4ksps - 7.8ksps
129 - 256
256
7.8ksps - 3.9ksps
257 - 512
512
3.9ksps - 2ksps
513 - 1024
1024
2ksps - 1ksps
1025 - 2048
2048
1ksps - 500sps
2049 - 4096
4096
488sps - 244sps
4097 - 8192
8192
244sps - 122sps
8193 - 16384
16384
122sps - 61sps
16385 - 32768
32768
61sps - 30.5sps
32769 - 65536
65536
30.5sps - 15.3sps
In cases where N/M < 1, achieving a full-scale output
result would require driving the analog inputs beyond
the specified guaranteed input differential voltage range.
Doing so is strongly discouraged since operation of the
LTC2368-24 beyond guaranteed specifications could result
in undesired behavior, possibly corrupting results. For
proper operation, it is recommended that the analog input
voltage not exceed the 0V to VREF specification. Note that
the output results do not saturate at N/M when N/M < 1.
50Hz and 60Hz Rejection
Particular input frequencies may be rejected by selecting
the appropriate number of averages, N, based on the
sampling rate, fSMPL, and the desired frequency to be
rejected, fREJECT. If,
TAVG =
1
fSMPL
•N=
1
fREJECT
236824f
22
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LTC2368-24
APPLICATIONS INFORMATION
then, D is an average value for a full sine wave cycle of
fREJECT, resulting in zero gain for that particular frequency
and integer multiples thereof up to fSMPL – fREJECT (See
Figure 18). Solving for N gives:
fSMPL
–40
fREJECT
Using this expression, we can find N for rejecting 50Hz
and 60Hz as well as other frequencies. Note that N and
fSMPL may be traded off to achieve rejection of particular
frequencies as shown below.
To reject 50Hz with fSMPL = 1Msps:
1,000,000sps
50Hz
= 20,000
To reject both 50Hz and 60Hz (each being a multiple of
10Hz), with N = 1024:
fSMPL = 1024 • 10Hz
–60
0
125 250 375 500 625 750 875 1000
FREQUENCY (kHz)
236824 F18
Figure 18. SINC1 Filter with fSMPL = 1Msps and N = 8
Count
N=
–20
GAIN (dB)
N=
0
= 10.24ksps
Figure 18 shows an example of a SINC1 filter where
fSMPL = 1Msps and N = 8, resulting in fREJECT = 125kHz.
Note that input frequencies above DC other than fREJECT
or multiples thereof are also attenuated to varying degrees
due to the averaging operation.
In addition to the 24-bit output code, a 16-bit WORD,
C[15:0], is appended to produce a total output WORD
of 40 bits, as shown in Figure 19. C[15:0] is the straight
binary representation (MSB first) of the number of samples
averaged to produce the output result minus one. For
instance, if N samples are averaged to produce the output
result, C[15:0] will equal N – 1. Thus, if N is 1 which is
the case with no averaging, C[15:0] will always be 0. If
N is 16384, then C[15:0] will equal 16383, and so on. If
more than 65536 samples are averaged, then C[15:0]
saturates at 65535.
CHAIN, RDL/SDI = 0
CNV
BUSY
POWER-DOWN AND ACQUIRE
CONVERT
SCK
SDO
D23 D22 D21 D20 D19 D18 D17 D16 D15 D14 D13 D12 D11 D10 D9 D8 D7 D6 D5 D4 D3 D2 D1 D0 C15 C14 C13 C12 C11 C10 C9 C8 C7 C6 C5
C4 C3 C2 C1 C0
236824 F19
DATA FROM CONVERSION
NUMBER OF SAMPLES
AVERAGED FOR DATA
Figure 19. Serial Output Code Parsing
236824f
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23
LTC2368-24
TIMING DIAGRAMS
Normal Mode, Single Device
SDO is driven. Figure 20 shows a single LTC2368-24
operated in normal mode with CHAIN and RDL/SDI tied
to ground. With RDL/SDI grounded, SDO is enabled and
the MSB(D23) of the output result is available tDSDOBUSYL
after the falling edge of BUSY. The count information is
shifted out after the output result.
When CHAIN = 0, the LTC2368-24 operates in normal
mode. In normal mode, RDL/SDI enables or disables the
serial data output pin SDO. If RDL/SDI is high, SDO is in
high impedance and SCK is ignored. If RDL/SDI is low,
CONVERT
CHAIN
DIGITAL HOST
CNV
BUSY
IRQ
LTC2368-24
RDL/SDI
SDO
SCK
DATA IN
CLK
236824 F20a
POWER-DOWN
AND ACQUIRE
CONVERT
CHAIN = 0
RDL/SDI = 0
POWER-DOWN AND ACQUIRE
CONVERT
tCYC
tCNVH
tCNVL
CNV
tACQ = tCYC – tCONV – tBUSYLH
tCONV
BUSY
tACQ
tBUSYLH
tSCK
1
SCK
2
3
SDO
C15
22
23
24
tSCKL
tHSDO
tDSDOBUSYL
tQUIET
tSCKH
tDSDO
D23
D22
D21
D1
D0
C15
236824 F20b
Figure 20. Using a Single LTC2368-24 in Normal Mode
236824f
24
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LTC2368-24
TIMING DIAGRAMS
Normal Mode, Multiple Devices
Since SDO is shared, the RDL/SDI input of each ADC must
be used to allow only one LTC2368-24 to drive SDO at a
time in order to avoid bus conflicts. As shown in Figure 21,
the RDL/SDI inputs idle high and are individually brought
low to read data out of each device between conversions.
When RDL/SDI is brought low, the MSB of the selected
device is output onto SDO. The count information is shifted
out after the output result.
Figure 21 shows multiple LTC2368-24 devices operating
in normal mode (CHAIN = 0) sharing CNV, SCK and SDO.
By sharing CNV, SCK and SDO, the number of required
signals to operate multiple ADCs in parallel is reduced.
RDLB
RDLA
CONVERT
CNV
CHAIN
RDL/SDI
LTC2368-24
B
SDO
RDL/SDI
SCK
DIGITAL HOST
CNV
CHAIN
BUSY
LTC2368-24
A
IRQ
SDO
SCK
DATA IN
CLK
236824 F21a
POWER-DOWN
AND ACQUIRE
CONVERT
POWER-DOWN AND ACQUIRE
CONVERT
CHAIN = 0
tCNVL
CNV
BUSY
tCONV
tBUSYLH
RDL/SDIA
RDL/SDIB
tSCK
1
SCK
tSCKH
2
3
tHSDO
tEN
SDO
Hi-Z
tQUIET
22
23
D22A
D21A
25
26
27
46
47
48
tSCKL
tDIS
tDSDO
D23A
24
D1A
D0A
Hi-Z
D23B
D22B
D21B
D1B
D0B
Hi-Z
236824 F21b
Figure 21. Normal Mode with Multiple Devices Sharing CNV, SCK and SDO
236824f
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25
LTC2368-24
TIMING DIAGRAMS
Chain Mode, Multiple Devices
number of converters. Figure 22 shows an example with
two daisy-chained devices. The MSB of converter A will
appear at SDO of converter B after 40 SCK cycles. The
MSB of converter A is clocked in at the RDL/SDI pin of
converter B on the rising edge of the first SCK pulse. The
functionality of the digital averaging filter is preserved
when in chain mode.
When CHAIN = OVDD, the LTC2368-24 operates in chain
mode. In chain mode, SDO is always enabled and RDL/
SDI serves as the serial data pin (SDI) where daisy-chain
data output from another ADC can be input.
This is useful for applications where hardware constraints
may limit the number of lines needed to interface to a large
OVDD
CONVERT
OVDD
CHAIN
RDL/SDI
CNV
CHAIN
LTC2368-24
A
SDO
SCK
RDL/SDI
DIGITAL HOST
CNV
LTC2368-24
B
BUSY
IRQ
SDO
SCK
DATA IN
CLK
236824 F22a
POWER-DOWN
AND ACQUIRE
CONVERT
POWER-DOWN AND ACQUIRE
CONVERT
CHAIN = OVDD
RDL/SDIA = 0
tCNVL
CNV
BUSY
tCONV
tBUSYLH
tSCKCH
1
SCK
2
3
38
39
tSSDISCK
40
41
tQUIET
42
43
78
79
80
tSCKL
tHSDO
tHSDISCK
SDOA = RDL/SDIB
tSCKH
tDSDO
D23A
D22A
D21A
C1A
C0A
D23B
D22B
D21B
C1B
C0B
tDSDOBUSYL
SDOB
D23A
D22A
D21A
C1A
C0A
236824 F22b
Figure 22. Chain Mode Timing Diagram
236824f
26
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LTC2368-24
BOARD LAYOUT
To obtain the best performance from the LTC2368-24
a printed circuit board is recommended. Layout for the
printed circuit board (PCB) should ensure the digital and
analog signal lines are separated as much as possible.
In particular, care should be taken not to run any digital
clocks or signals alongside analog signals or underneath
the ADC.
Supply bypass capacitors should be placed as close as
possible to the supply pins. Low impedance common re-
turns for these bypass capacitors are essential to the low
noise operation of the ADC. A single solid ground plane
is recommended for this purpose. When possible, screen
the analog input traces using ground.
Reference Design
For a detailed look at the reference design for this converter, including schematics and PCB layout, please refer
to DC2289, the evaluation kit for the LTC2368-24.
236824f
For more information www.linear.com/LTC2368-24
27
LTC2368-24
PACKAGE DESCRIPTION
Please refer to http://www.linear.com/product/LTC2368-24#packaging for the most recent package drawings.
DE Package
16-Lead Plastic DFN (4mm × 3mm)
(Reference LTC DWG # 05-08-1732 Rev Ø)
0.70 ±0.05
3.30 ±0.05
3.60 ±0.05
2.20 ±0.05
1.70 ±0.05
PACKAGE
OUTLINE
0.25 ±0.05
0.45 BSC
3.15 REF
RECOMMENDED SOLDER PAD PITCH AND DIMENSIONS
APPLY SOLDER MASK TO AREAS THAT ARE NOT SOLDERED
4.00 ±0.10
(2 SIDES)
R = 0.05
TYP
9
R = 0.115
TYP
0.40 ±0.10
16
3.30 ±0.10
3.00 ±0.10
(2 SIDES)
1.70 ±0.10
PIN 1 NOTCH
R = 0.20 OR
0.35 × 45°
CHAMFER
PIN 1
TOP MARK
(SEE NOTE 6)
(DE16) DFN 0806 REV Ø
8
0.200 REF
1
0.23 ±0.05
0.45 BSC
0.75 ±0.05
3.15 REF
0.00 – 0.05
BOTTOM VIEW—EXPOSED PAD
NOTE:
1. DRAWING PROPOSED TO BE MADE VARIATION OF VERSION (WGED-3) IN JEDEC
PACKAGE OUTLINE MO-229
2. DRAWING NOT TO SCALE
3. ALL DIMENSIONS ARE IN MILLIMETERS
4. DIMENSIONS OF EXPOSED PAD ON BOTTOM OF PACKAGE DO NOT INCLUDE
MOLD FLASH. MOLD FLASH, IF PRESENT, SHALL NOT EXCEED 0.15mm ON ANY SIDE
5. EXPOSED PAD SHALL BE SOLDER PLATED
6. SHADED AREA IS ONLY A REFERENCE FOR PIN 1 LOCATION ON THE
TOP AND BOTTOM OF PACKAGE
236824f
28
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LTC2368-24
PACKAGE DESCRIPTION
Please refer to http://www.linear.com/product/LTC2368-24#packaging for the most recent package drawings.
MS Package
16-Lead Plastic MSOP
(Reference LTC DWG # 05-08-1669 Rev A)
0.889 ±0.127
(.035 ±.005)
5.10
(.201)
MIN
3.20 – 3.45
(.126 – .136)
4.039 ±0.102
(.159 ±.004)
(NOTE 3)
0.50
(.0197)
BSC
0.305 ±0.038
(.0120 ±.0015)
TYP
RECOMMENDED SOLDER PAD LAYOUT
0.254
(.010)
DETAIL “A”
3.00 ±0.102
(.118 ±.004)
(NOTE 4)
4.90 ±0.152
(.193 ±.006)
0° – 6° TYP
0.280 ±0.076
(.011 ±.003)
REF
16151413121110 9
GAUGE PLANE
0.53 ±0.152
(.021 ±.006)
DETAIL “A”
0.18
(.007)
SEATING
PLANE
1.10
(.043)
MAX
0.17 – 0.27
(.007 – .011)
TYP
1234567 8
0.50
(.0197)
BSC
NOTE:
1. DIMENSIONS IN MILLIMETER/(INCH)
2. DRAWING NOT TO SCALE
3. DIMENSION DOES NOT INCLUDE MOLD FLASH, PROTRUSIONS OR GATE BURRS.
MOLD FLASH, PROTRUSIONS OR GATE BURRS SHALL NOT EXCEED 0.152mm (.006") PER SIDE
4. DIMENSION DOES NOT INCLUDE INTERLEAD FLASH OR PROTRUSIONS.
INTERLEAD FLASH OR PROTRUSIONS SHALL NOT EXCEED 0.152mm (.006") PER SIDE
5. LEAD COPLANARITY (BOTTOM OF LEADS AFTER FORMING) SHALL BE 0.102mm (.004") MAX
0.86
(.034)
REF
0.1016 ±0.0508
(.004 ±.002)
MSOP (MS16) 0213 REV A
236824f
Information furnished by Linear Technology Corporation is believed to be accurate and reliable.
However, no responsibility is assumed for its use. Linear Technology Corporation makes no representation that the interconnection
of itsinformation
circuits as described
herein will not infringe on existing patent rights.
For more
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29
LTC2368-24
TYPICAL APPLICATION
Using the LTC2368-24 in a Low Side Current Sensing Application
8V
LOAD
ILOAD
3
+
VSENSE
–
RSENSE = 100Ω
2
7
+
LTC2057
–
6
10Ω
IN+
LTC2368-24
4.7µF
4
IN–
–3.6V
236824 TA02
0.047µF
208Ω
4.99k
RELATED PARTS
PART NUMBER
DESCRIPTION
COMMENTS
ADCs
LTC2380-24
24-Bit, 1.5Msps/2Msps Serial, Low Power ADC 2.5V Supply, Differential Input, Digital Filter, 100dB SNR, ±5V Input Range,
DGC, MSOP-16 and 4mm × 3mm DFN-16 Packages
LTC2378-20/LTC2377-20/ 20-Bit, 1Msps/500ksps/250ksps, ±0.5ppm
LTC2376-20
INL Serial, Low Power ADC
2.5V Supply, ±5V Fully Differential Input, 104dB SNR, MSOP-16 and
4mm × 3mm DFN-16 Packages
LTC2379-18/LTC2378-18/ 18-Bit, 1.6Msps/1Msps/500ksps/250ksps
LTC2377-18/LTC2376-18 Serial, Low Power ADC
2.5V Supply, Differential Input, 101.2dB SNR, ±5V Input Range, DGC,
Pin-Compatible Family in MSOP-16 and 4mm × 3mm DFN-16 Packages
LTC2380-16/LTC2378-16/ 16-Bit, 2Msps/1Msps/500ksps/250ksps
LTC2377-16/LTC2376-16 Serial, Low Power ADC
2.5V Supply, Differential Input, 96.2dB SNR, ±5V Input Range, DGC,
Pin-Compatible Family in MSOP-16 and 4mm × 3mm DFN-16 Packages
LTC2369-18/LTC2368-18/ 18-Bit, 1.6Msps/1Msps/500ksps/250ksps
LTC2367-18/LTC2364-18 Serial, Low Power ADC
2.5V Supply, Pseudo-Differential Unipolar Input, 96.5dB SNR, 0V to 5V Input
Range, Pin-Compatible Family in MSOP-16 and 4mm × 3mm DFN-16 Packages
LTC2370-16/LTC2368-16/ 16-Bit, 2Msps/1Msps/500ksps/250ksps
LTC2367-16/LTC2364-16 Serial, Low Power ADC
2.5V Supply, Pseudo-Differential Unipolar Input, 94dB SNR, 0V to 5V Input
Range, Pin-Compatible Family in MSOP-16 and 4mm × 3mm DFN-16 Packages
DACs
LTC2757
18-Bit, Single Parallel IOUT SoftSpan™ DAC
±1LSB INL/DNL, Software-Selectable Ranges, 7mm × 7mm LQFP-48 Package
LTC2641
16-Bit/14-Bit/12-Bit Single Serial VOUT DAC
±1LSB INL/DNL, MSOP-8 Package, 0V to 5V Output
LTC2630
12-Bit/10-Bit/8-Bit Single VOUT DACs
SC70 6-Pin Package, Internal Reference, ±1LSB INL (12 Bits)
LTC6655
Precision Low Drift Low Noise Buffered
Reference
5V/4.906V/3.3V/3V/2.5V/2.048V/1.25V, 2ppm/°C, 0.25ppm Peak-to-Peak
Noise, MSOP-8 Package
LTC6652
Precision Low Drift Low Noise Buffered
Reference
5V/4.906V/3.3V/3V/2.5V/2.048V/1.25V, 5ppm/°C, 2.1ppm Peak-to-Peak Noise,
MSOP-8 Package
REFERENCES
AMPLIFIERS
LT6203/LT6202
Dual/Single 100MHz Rail-to-Rail Input/Output 1.9nV/√Hz, 3mA Maximum Supply Current, 100MHz Gain Bandwidth
Low Noise Power Amplifiers
LT6237/LT6236
Dual/Single Rail-to-Rail Output ADC Driver
215MHz GBW, 1.1nV/√Hz, 3.5mA Supply Current
LTC2057
Zero-Drift Rail-to-Rail Output Operational
Amplifier
4µV (Max) Offset Voltage, 0.015µV/°C Offset Voltage Drift
236824f
30 Linear Technology Corporation
1630 McCarthy Blvd., Milpitas, CA 95035-7417
For more information www.linear.com/LTC2368-24
(408) 432-1900 ● FAX: (408) 434-0507
●
www.linear.com/LTC2368-24
LT 1215 • PRINTED IN USA
LINEAR TECHNOLOGY CORPORATION 2015
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湘ICP备2023018690号
