L7L|nt “I2 LTC2315-12 TECHNOLOGY WI | L7 LJUW 1
LTC2315-12
1
231512fa
For more information www.linear.com/LTC2315-12
TYPICAL APPLICATION
FEATURES DESCRIPTION
12-Bit, 5Msps Serial
Sampling ADC in TSOT
The LTC
®
2315-12 is a 12-bit, 5Msps, serial sampling A/D
converter that draws only 6.4mA from a wide range analog
supply adjustable from 2.7V to 5.25V. The LTC2315-12
contains an integrated bandgap and reference buffer which
provide a low cost, high performance (20ppm/°C max)
and space saving applications solution. The LTC2315-12
achieves outstanding AC performance of 72.6dB SINAD
and 84dB THD while sampling a 500kHz input frequency.
The extremely high sample rate-to-power ratio makes the
LTC2315-12 ideal for compact, low power, high speed
systems. The LTC2315-12 also provides both nap and
sleep modes for further optimization of the device power
within a system.
The LTC2315-12 has a high-speed SPI-compatible serial
interface that supports 1.8V, 2.5V, 3V and 5V logic. The
fast 5Msps throughput makes the LTC2315-12 ideally
suited for a wide variety of high speed applications.
Complete 14-/12-Bit Pin-Compatible SAR ADC Family
500ksps 2.5Msps 4.5Msps 5Msps
14-Bit LTC2312-14 LTC2313-14 LTC2314-14
12-Bit LTC2312-12 LTC2313-12 LTC2315-12
Power 3V/5V 9mW/15mW 14mW/25mW 18mW/31mW 19mW/32mW
APPLICATIONS
n 5Msps Throughput Rate
n Guaranteed 12-Bit No Missing Codes
n Internal Reference: 2.048V/4.096V Span
n Low Noise: 73dB SNR
n Low Power: 6.4mA at 5Msps and 5V
n Dual Supply Range: 3V/5V operation
n Sleep Mode with < 1µA Typical Supply Current
n Nap Mode with Quick Wake-up < 1 conversion
n Separate 1.8V to 5V Digital I/O Supply
n High Speed SPI-Compatible Serial I/O
n Guaranteed Operation from –40°C to 125°C
n 8-Lead TSOT-23 Package
n Communication Systems
n High Speed Data Acquisition
n Handheld Terminal Interface
n Medical Imaging
n Uninterrupted Power Supplies
n Battery Operated Systems
n Automotive
L, LT, LT C , LT M, Linear Technology and the Linear logo are registered trademarks of Linear
Technology Corporation. All other trademarks are the property of their respective owners.
5V Supply, Internal Reference, 5Msps, 12-bit Sampling ADC
SERIAL DATA LINK TO
ASIC, PLD, MPU, DSP
OR SHIFT REGISTERS
ANALOG INPUT
0V TO 4.096V
5V
2.2µF
2.2µF
2.2µF
231512 TA01
GND
VDD
REF
AIN OVDD
SCK
CS
SDO
LTC2315-12
DIGITAL OUTPUT SUPPLY
1.8V TO 5V
16k Point FFT, fS = 5Msps, fIN = 500kHz
231512 TA01a
FREQUENCY (kHz)
AMPLITUDE (dBFS)
0 25002000
1000500 1500
0
–20
–40
–60
–80
–100
–120
–140
VDD = 5V
SNR = 73.1dBFS
SINAD = 72.6dBFS
THD = –84dB
SFDR = 87dBc
LTC2315—1 2 WW UUUU 2 L7LJ1‘JW
LTC2315-12
2
231512fa
For more information www.linear.com/LTC2315-12
PIN CONFIGURATIONABSOLUTE MAXIMUM RATINGS
Supply Voltage (VDD, OVDD) .......................................6V
Reference (REF) and Analog Input (AIN) Voltage
(Note 3) ......................................(–0.3V) to (VDD + 0.3V)
Digital Input Voltage (Note 3) .. (–0.3V) to (OVDD + 0.3V)
Digital Output Voltage ............. (–0.3V) to (OVDD + 0.3V)
Power Dissipation ...............................................100mW
Operating Temperature Range
LTC2315C ................................................ C to 70°C
LTC2315I ..............................................40°C to 8C
LTC2315H .......................................... 40°C to 125°C
Storage Temperature Range .................. 65°C to 150°C
Lead Temperature Range (Soldering, 10 sec) ........30C
(Notes 1, 2)
1
2
3
4
8
7
6
5
TOP VIEW
TS8 PACKAGE
8-LEAD PLASTIC TSOT-23
CS
SCK
SDO
OVDD
VDD
REF
GND
AIN
TJMAX = 150°C, θJA = 195°C/W
ORDER INFORMATION
Lead Free Finish
TAPE AND REEL (MINI) TAPE AND REEL PART MARKING* PACKAGE DESCRIPTION TEMPERATURE RANGE
LTC2315CTS8-12#TRMPBF LTC2315CTS8-12#TRPBF LTFZG 8-Lead Plastic TSOT-23 0°C to 70°C
LTC2315ITS8-12#TRMPBF LTC2315ITS8-12#TRPBF LTFZG 8-Lead Plastic TSOT-23 –40˚C to 85˚C
LTC2315HTS8-12#TRMPBF LTC2315HTS8-12#TRPBF LTFZG 8-Lead Plastic TSOT-23 –40˚C to 125˚C
TRM = 500 pieces. *Temperature grades are identified by a label on the shipping container.
Consult LTC Marketing for parts specified with wider operating temperature ranges.
Consult LTC Marketing for information on lead based finish parts.
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/
LTC231 5—1 2 L7 LJUW 3
LTC2315-12
3
231512fa
For more information www.linear.com/LTC2315-12
ELECTRICAL CHARACTERISTICS
CONVERTER CHARACTERISTICS
DYNAMIC ACCURACY
SYMBOL PARAMETER CONDITIONS MIN TYP MAX UNITS
VAIN Absolute Input Range l–0.05 VDD + 0.05 V
VIN Input Voltage Range (Note 11) 0 VREF V
IIN Analog Input DC Leakage Current l–1 1 µA
CIN Analog Input Capacitance Sample Mode
Hold Mode
13
3
pF
pF
SYMBOL PARAMETER CONDITIONS MIN TYP MAX UNITS
Resolution l12 Bits
No Missing Codes l12 Bits
Transition Noise (Note 6) 0.33 LSBRMS
INL Integral Linearity Error VDD = 5V (Note 5)
VDD = 3V (Note 5)
l
l
–1.25
–1.5
±0.25
±0.3
1.25
1.5
LSB
LSB
DNL Differential Linearity Error VDD = 5V
VDD = 3V
l
l
–0.99
–0.99
±0.15
±0.2
0.99
0.99
LSB
LSB
Offset Error VDD = 5V
VDD = 3V
l
l
–4
–6
±0.5
±1
4
6
LSB
LSB
Full-Scale Error VDD = 5V
VDD = 3V
l
l
–7
–9
±1.5
±2
7
9
LSB
LSB
Total Unadjusted Error VDD = 5V
VDD = 3V
l
l
–8
–10
±2
±2.5
8
10
LSB
LSB
SYMBOL PARAMETER CONDITIONS MIN TYP MAX UNITS
SINAD Signal-to-(Noise + Distortion) Ratio fIN = 500kHz, VDD = 5V
fIN = 500kHz, VDD = 3V
l
l
69.5
67.5
72.6
69.5
dB
dB
SNR Signal-to-Noise Ratio fIN = 500kHz, VDD = 5V
fIN = 500kHz, VDD = 3V
l
l
70
68
73
70
dB
dB
THD Total Harmonic Distortion
First 5 Harmonics
fIN = 500kHz, VDD = 5V
fIN = 500kHz, VDD = 3V
l
l
–84
–84
–76
–75
dB
dB
SFDR Spurious Free Dynamic Range fIN = 500kHz, VDD = 5V
fIN = 500kHz, VDD = 3V
l
l
87
87
78
77
dB
dB
IMD Intermodulation Distortion
2nd Order Terms
3rd Order Terms
fIN1 = 461kHz, fIN2 = 541kHz
AIN1, AIN2 = –7dBFS
–77
–89
dBc
dBc
Full Power Bandwidth At 3dB
At 0.1dB
130
20
MHz
MHz
–3dB Input Linear Bandwidth SINAD ≥ 68dB 5 MHz
tAP Aperture Delay 1 ns
tJITTER Aperture Jitter 10 psRMS
The l denotes the specifications which apply over the full operating
temperature range, otherwise specifications are at TA = 25°C. (Note 4)
The l denotes the specifications which apply over the full operating
temperature range, otherwise specifications are at TA = 25°C. (Note 4)
The l denotes the specifications which apply over the full operating temperature range,
otherwise specifications are at TA = 25°C and AIN = –1dBFS. (Note 4)
LTC2315—1 2 4 L7LJ1W
LTC2315-12
4
231512fa
For more information www.linear.com/LTC2315-12
REFERENCE INPUT/OUTPUT
POWER REQUIREMENTS
DIGITAL INPUTS AND DIGITAL OUTPUTS
SYMBOL PARAMETER CONDITIONS MIN TYP MAX UNITS
VREF VREF Output Voltage 2.7V ≤ VDD ≤ 3.6V
4.75 ≤ VDD ≤ 5.25V
l
l
2.040
4.080
2.048
4.096
2.056
4.112
V
V
VREF Temperature Coefficient l7 20 ppm/°C
VREF Output Resistance Normal Operation
Overdrive Condition
(VREFIN ≥ VREFOUT + 50mV)
2
52
Ω
VREF Line Regulation 2.7V ≤ VDD ≤ 3.6V
4.75 ≤ VDD ≤ 5.25V
2
0.8
mV/V
mV/V
VREF 2.048V/4.096V Supply Threshold 4.15 V
VREF 2.048V/4.096V Supply Threshold Hysteresis 150 mV
VREF Input Voltage Range
(External Reference Input)
2.7V ≤ VDD ≤ 3.6V
4.75 ≤ VDD ≤ 5.25V
l
l
VREF + 50mV
VREF + 50mV
VDD
4.3
V
V
SYMBOL PARAMETER CONDITIONS MIN TYP MAX UNITS
VDD Supply Voltage
3V Operational Range
5V Operational Range
l
l
2.7
4.75
3
5
3.6
5.25
V
V
OVDD Digital Output Supply Voltage l1.71 5.25 V
ITOTAL =
IVDD + IOVDD
Supply Current, Static Mode
Operational Mode
Nap Mode
Sleep Mode
CS = 0V, SCK = 0V l
l
l
3.5
6.4
1.8
0.8
4
7.5
5
mA
mA
mA
µA
PDPower Dissipation, Static Mode
Operational Mode
Nap Mode
Sleep Mode
CS = 0V, SCK = 0V l
l
l
17.5
32
9
4
20
37.5
25
mW
mW
mW
µW
SYMBOL PARAMETER CONDITIONS MIN TYP MAX UNITS
VIH High Level Input Voltage l0.8 • OVDD V
VIL Low Level Input Voltage l0.2 • OVDD V
IIN Digital Input Current VIN = 0V to OVDD l–10 10 μA
CIN Digital Input Capacitance 5 pF
VOH High Level Output Voltage IO = –500µA (Source) lOVDD–0.2 V
VOL Low Level Output Voltage IO = 500µA (Sink) l0.2 V
IOZ High-Z Output Leakage Current VOUT = 0V to OVDD, CS = High l–10 10 µA
COZ High-Z Output Capacitance CS = High 4 pF
ISOURCE Output Source Current VOUT = 0V, OVDD = 1.8V –20 mA
ISINK Output Sink Current VOUT = OVDD = 1.8V 20 mA
The l denotes the specifications which apply over the full operating temperature
range, otherwise specifications are at TA = 25°C. (Note 4)
The l denotes the specifications which apply over the full operating temperature
range, otherwise specifications are at TA = 25°C. (Note 4)
The l denotes the specifications which apply over the
full operating temperature range, otherwise specifications are at TA = 25°C. (Note 4)
LTC231 5—1 2 L7 LJUW 5
LTC2315-12
5
231512fa
For more information www.linear.com/LTC2315-12
ADC TIMING CHARACTERISTICS
SYMBOL PARAMETER CONDITIONS MIN TYP MAX UNITS
fSAMPLE(MAX) Maximum Sampling Frequency (Notes 7, 8) l5 MHz
fSCK Shift Clock Frequency (Notes 7, 8) l87.5 MHz
tSCK Shift Clock Period l11.4 ns
tTHROUGHPUT Minimum Throughput Time, tACQ + tCONV l200 ns
tCONV Conversion Time l160 ns
tACQ Acquisition Time l40 ns
t1Minimum CS Pulse Width (Note 7) l5 ns
t2SCK
Setup Time After CS(Note 7) l5 ns
t3SDO Enable Time After CS(Notes 7, 8) l10 ns
t4SDO Data Valid Access Time after SCK(Notes 7, 8, 9) l9.1 ns
t5SCLK Low Time l4.5 ns
t6SCLK High Time l4.5 ns
t7SDO Data Valid Hold Time After SCK(Notes 7, 8, 9) l1 ns
t8SDO into Hi-Z State Time After 16th SCK(Notes 7, 8, 10) l3 10 ns
t9SDO into Hi-Z State Time After CS(Notes 7, 8, 10) l3 10 ns
t10 CS Setup Time After 14th SCK(Note 7) l5 ns
Latency l1 Cycle Latency
tWAKE_NAP Power-Up Time from Nap Mode See Nap Mode Section 50 ns
tWAKE_SLEEP Power-Up Time from Sleep Mode See Sleep Mode Section 1.1 ms
The l denotes the specifications which apply over the full operating
temperature range, otherwise specifications are at TA = 25°C. (Note 4)
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 VDD
(AIN, REF) or OVDD (SCK, CS, SDO) they will be clamped by internal
diodes. This product can handle input currents up to 100mA below ground
or above VDD or OVDD without latch-up.
Note 4. VDD = 5V, OVDD = 2.5V, fSMPL = 5MHz, fSCK = 87.5MHz, AIN =
–1dBFS and internal reference unless otherwise noted.
Note 5. 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 6. Typical RMS noise at code transitions.
Note 7. Parameter tested and guaranteed at OVDD = 2.5V. All input signals
are specified with tr = tf = 1nS (10% to 90% of OVDD) and timed from a
voltage level of OVDD/2.
Note 8. All timing specifications given are with a 10pF capacitance load.
Load capacitances greater than this will require a digital buffer.
Note 9. The time required for the output to cross the VIH or VIL voltage.
Note 10. Guaranteed by design, not subject to test.
Note 11. Recommended operating conditions.
LTC2315—12 \\ II /I If II I I II H II E4 ”I
LTC2315-12
6
231512fa
For more information www.linear.com/LTC2315-12
TYPICAL PERFORMANCE CHARACTERISTICS
16k Point FFT, fS = 5Msps
fIN = 500kHz
SNR, SINAD vs Input Frequency
(100kHz to 2.2MHz)
THD, Harmonics vs Input
Frequency (100kHz to 2.2MHz)
THD, Harmonics vs Input
Frequency (100kHz to 2.2MHz)
SNR, SINAD vs Temperature,
fIN = 500kHz
THD, Harmonics vs Temperature,
fIN = 500kHz
Integral Nonlinearity
vs Output Code
Differential Nonlinearity
vs Output Code
DC Histogram Near Mid-Scale
(Code 2048)
TA = 25°C, VDD = 5V, OVDD = 2.5V, fSMPL = 5Msps,
unless otherwise noted.
OUTPUT CODE
0
–1.0
–0.8
–0.6
–0.4
DNL (LSB)
–0.2
0.4
0.2
0.0
0.6
0.8
1.0
1024 2048 3072 4096
231512 G02
CODE
2047
COUNTS
2049
231512 G03
2048 2050 2051
σ = 0.33
0
10000
20000
30000
40000
60000
50000
231512 G04
INPUT FREQUENCY (kHz)
AMPLITUDE (dBFS)
0 25002000
1000500 1500
0
–20
–40
–60
–80
–100
–120
–140
VDD = 5V
SNR = 73.1dBFS
SINAD = 72.6dBFS
THD = –84dB
SFDR = 87dBc
INPUT FREQUENCY (kHz)
0
69
70
SNR, SINAD (dBFS)
71
72
73
74
500 1000 1500 2000 2500
231512 G05
SINAD
SNR
SINAD
SNR
VDD = 5V
VDD = 3V
INPUT FREQUENCY (kHz)
0
–100
–95
THD, HARMONICS (dB)
–90
–85
–80
–75
500 1000 1500 2000 2500
231512 G06
THD
2ND
3RD
RIN/CIN = 50Ω/47pF
fS = 5Msps
VDD = 3V
TEMPERATURE (°C)
–55 –35
68
70
69
SNR, SINAD (dBFS)
71
72
74
73
75
–15 5 25 45 65 85 105 125
231512 G07
SNR
SNR
SINAD
SINAD
VDD = 5V
VDD = 3V
TEMPERATURE (°C)
–55 –35
–100
–95
THD, HARMONICS (dB)
–90
–85
–80
–75
–15 5 25 45 65 85 105 125
231512 G08
THD
3RD
2ND
VDD = 3V
OUTPUT CODE
0
–1.0
–0.8
–0.6
–0.4
INL (LSB)
–0.2
0.4
0.2
0.0
0.6
0.8
1.0
1024 2048 3072 4096
231512 G01
INPUT FREQUENCY (kHz)
0
–100
–95
THD, HARMONICS (dB)
–90
–85
–80
–75
500 1000 1500 2000 2500
231512 G06a
THD
2ND
3RD
RIN/CIN = 50Ω/47pF
fS = 5Msps
VDD = 5V
LTC231 5—1 2 11 2114‘ 1‘ ‘ ll "——+4_ L7 HEW
LTC2315-12
7
231512fa
For more information www.linear.com/LTC2315-12
TYPICAL PERFORMANCE CHARACTERISTICS
Supply Current vs Temperature
Shutdown Current vs Temperature Supply Current vs SCK Frequency
Reference Current
vs Reference Voltage
Full-Scale Error vs Temperature Offset Error vs Temperature
SNR, SINAD vs Reference Voltage
fIN = 500kHz
THD, Harmonics vs Temperature,
fIN = 500kHz
TA = 25°C, VDD = 5V, OVDD = 2.5V, fSMPL = 5Msps,
unless otherwise noted.
REFERENCE VOLTAGE (V)
2
70
SNR, SINAD (dBFS)
71
72
73
74
2.5 3 3.5 4 4.5
231512 G10
SNR
SNR
SINAD
SINAD
VDD = 3.6V
OPERATION
NOT ALLOWED
VDD = 5V
REFERENCE VOLTAGE (V)
2
0
REFERENCE CURRENT (µA)
200
100
300
400
500
600
2.5 3 3.5 4 4.5
231512 G11
VDD = 3.6V
fS = 5Msps
fS = 5Msps
fS = 3Msps
fS = 3Msps
OPERATION
NOT ALLOWED
VDD = 5V
TEMPERATURE (°C)
–55
–4
FULL-SCALE ERROR (LSB)
–1
0
–3
–2
1
2
3
4
–35 –15 5 4525 8565 105 125
231512 G12
TEMPERATURE (°C)
–55
–1
OFFSET ERROR (LSB)
0
–0.5
0.5
1
–35 –15 5 4525 8565 105 125
231512 G13
TEMPERATURE (°C)
–55
5
SUPPLY CURRENT (mA)
5.75
5.5
5.25
6
6.5
6.25
–35 –15 5 4525 8565 105 125
231512 G14
VDD = 5V
VDD = 3V
TEMPERATURE (°C)
–55
0
SHUTDOWN CURRENT (µA)
0.25
0.5
1
0.75
–35 –15 5 4525 8565 105 125
231512 G15
VDD = 5V
VDD = 3V
IVDD + IOVDD
SCK FREQUENCY (MHz)
10
0
SUPPLY CURRENT (mA)
2
4
7
5
3
1
6
20 30 5040 7060 80 90
231512 G16
ITOT
IVDD
VDD = 3V
OVDD = 1.8V
IOVDD
TEMPERATURE (°C)
–55 –35
–100
–95
THD, HARMONICS (dB)
–90
–85
–80
–75
–15 5 25 45 65 85 105 125
231512 G08a
THD
3RD
2ND
VDD = 5V
LTC2315—1 2 ‘ ‘ \ 1 1/7 MH 1 ‘ /1 sax ‘ ‘ ‘ ‘ 7 T / ,v’ / /,_ —_/ MHzl 1 ’ r‘ i , ‘ , ‘,/ / 8 L7LJ1‘JW
LTC2315-12
8
231512fa
For more information www.linear.com/LTC2315-12
TA = 25°C, VDD = 5V, OVDD = 2.5V, fSMPL = 5Msps,
unless otherwise noted.
TYPICAL PERFORMANCE CHARACTERISTICS
PIN FUNCTIONS
VDD (Pin 1): Power Supply. The ranges of VDD are 2.7V
to 3.6V and 4.75V to 5.25V. Bypass VDD to GND with a
2.2µF ceramic chip capacitor.
REF (Pin 2): Reference Input/Output. The REF pin volt-
age defines the input span of the ADC, 0V to VREF. By
default, REF is an output pin and produces a reference
voltage VREF of either 2.048V or 4.096V depending on
VDD (see Table 2). Bypass to GND with a 2.2µF, low ESR,
high quality ceramic chip capacitor. The REF pin may be
overdriven with a voltage at least 50mV higher than the
internal reference voltage output.
GND (Pin 3): Ground. The GND pin must be tied directly
to a solid ground plane.
AIN (Pin 4): Analog Input. AIN is a single-ended input with
respect to GND with a range from 0V to VREF.
OVDD (Pin 5): I/O Interface Digital Power. The OVDD range
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 to GND with a 2.2µF ceramic chip capacitor.
SDO (Pin 6): Serial Data Output. The A/D conversion result
is shifted out on SDO as a serial data stream with the MSB
first through the LSB last. There is 1 cycle of conversion
latency. Logic levels are determined by OVDD.
SCK (Pin 7): Serial Data Clock Input. The SCK serial clock
falling edge advances the conversion process and outputs
a bit of the serialized conversion result, MSB first to LSB
last. SDO data transitions on the falling edge of SCK. A
continuous or burst clock may be used. Logic levels are
determined by OVDD.
CS (Pin 8): Chip Select Input. This active low signal starts
a conversion on the falling edge and frames the serial data
transfer. Bringing CS high places the sample-and-hold
into sample mode and also forces the SDO pin into high
impedance. Logic levels are determined by OVDD.
Output Supply Current (IOVDD)
vs Output Supply Voltage (OVDD)
OUTPUT SUPPLY VOLTAGE (V)
1.7
0
OUTPUT SUPPLY CURRENT (mA)
0.5
1.0
2.5
2.0
1.5
2.92.3 4.13.5 4.7 5.3
231512 G18
5Msps
fSCK = 87.5MHz
3Msps
fSCK = 52.5MHz
Supply Current (IVDD)
vs Supply Voltage (VDD)
SUPPLY VOLTAGE (V)
2.6
4.50
SUPPLY CURRENT (mA)
5.25
5.00
4.75
5.50
5.75
6.00
6.50
6.25
2.9 3.83.53.2 4.1 4.74.4 5.35.0
231512 G17
5Msps
fSCK = 87.5MHz
3Msps
fSCK = 52.5MHz
OPERATION
NOT ALLOWED
5Msps
3Msps
LTC231 5—1 2 1 {J .IEL —cJ £5 E: £4— £1— :>C :X: £11519; 4 fig L7 LJUW 9
LTC2315-12
9
231512fa
For more information www.linear.com/LTC2315-12
TIMING DIAGRAMS
231512 TD04231512 TD03
231512 TD02231512 TD01
Hi-Z
SCK OVDD/2
SDO
t8
16TH EDGE
Hi-Z
CS OVDD/2
SDO
t9
VOH
VOL
SCK OVDD/2
SDO
t7
VOH
VOL
SCK OVDD/2
SDO
t4
Figure 1. SDO Into Hi-Z after 16TH SCK
Figure 3. SDO Data Valid Hold after SCK
Figure 2. SDO Into Hi-Z after CS
Figure 4. SDO Data Valid Access after SCK
tTHROUGHPUT
tACQ-MIN
tACQ-MIN = 40ns
tCONV
tCONV = 13.5 • tSCK + t2 + t10
1413124321
CS
SCK
SDO HI-Z STATE
(MSB)
*NOTE: SDO REPRESENTS THE ANALOG INPUT FROM THE PREVIOUS CONVERSION
B0 0B9B10B11*0
231512 TD05
t5
t6
t2
t4t7t9
t3
t10
Figure 5: LTC2315-12 Serial Interface Timing Diagram (SCK Low During tACQ)
BLOCK DIAGRAM
231512 BD
4
+
S/H
2.5V LDO
2×/4×1.024V
BANDGAP
TIMING
LOGIC
1
6
7
8
THREE-STATE
SERIAL
OUTPUT
PORT
12-BIT SAR ADC
2
3
AIN
REF
VDD OVDD
2.2µF GND
ANALOG
INPUT RANGE
0V TO VREF
ANALOG SUPPLY
RANGE 2.7V TO 5.25V
DIGITAL SUPPLY
RANGE 1.71V TO 5.25V
5
2.2µF2.2µF
SDO
SCK
CS
TS8 PACKAGE
ALL CAPACITORS UNLESS
NOTED ARE HIGH QUALITY,
CERAMIC CHIP TYPE
LTC2315—1 2 9mm » 9 9L 4L —fl 1 O L7ELUEN2
LTC2315-12
10
231512fa
For more information www.linear.com/LTC2315-12
tTHROUGHPUT
tACQ-MIN
tACQ-MIN = 40ns
tCONV
tCONV(MIN) = 13 • tSCK + t2 + t10
141354321
CS
SCK
SDO HI-Z STATE
(MSB)
*NOTE: SDO REPRESENTS THE ANALOG INPUT FROM THE PREVIOUS CONVERSION
B0 0B1B9B10B11*00
231512 TD06
t5
t6
t2
t4t7
t10
t9
t3
Figure 6: LTC2315-12 Serial Interface Timing Diagram (SCK High During tACQ)
tTHROUGHPUT = 18 • tSCK
tACQ
tACQ = 4 • tSCK
tCONV
tCONV = 14 • tSCK
13 14 15 16 17 1818 4 5321
CS
SCK
SDO HI-Z STATE
(MSB)
*NOTE: SDO REPRESENTS THE ANALOG INPUT FROM THE PREVIOUS CONVERSION
B1 B0 0B9B10B11*00
231512 TD07
t5
t6
t2
t4t7
t10
t9
t3
Figure 7: LTC2315-12 Serial Interface Timing Diagram (SCK Continuous)
TIMING DIAGRAMS
LTC231 5—1 2 L7 LJUW 1 1
LTC2315-12
11
231512fa
For more information www.linear.com/LTC2315-12
APPLICATIONS INFORMATION
Overview
The LT C
®
2315-12 is a low noise, high speed, 12-bit succes-
sive approximation register (SAR) ADC. The LTC2315-12
operates over a wide supply range (2.7V to 5.25V) and
provides a low drift (20ppm/°C maximum), internal refer-
ence and reference buffer. The internal reference buffer is
automatically configured to a 2.048V span in low supply
range (2.7V to 3.6V) and to a 4.096V span in the high
supply range (4.75V to 5.25V). The LTC2315-12 samples
at a 5Msps rate and supports an 87.5MHz data clock. The
LTC2315-12 achieves excellent dynamic performance
(73dB SNR, 84dB THD) while dissipating only 32mW from
a 5V supply at the 5Msps conversion rate.
The LTC2315-12 outputs the conversion data with one
cycle of conversion latency on the SDO pin. The SDO pin
output logic levels are supplied by the dedicated OVDD
supply pin which has a wide supply range (1.71V to 5.25V)
allowing the LTC2315-12 to communicate with 1.8V, 2.5V,
3V or 5V systems.
The LTC2315-12 provides both nap and sleep power-down
modes through serial interface control to reduce power
dissipation during inactive periods.
Serial Interface
The LT2315-12 communicates with microcontrollers, DSPs
and other external circuitry via a 3-wire interface. A falling
CS edge starts a conversion and frames the serial data
transfer. SCK provides the conversion clock for the current
sample and controls the data readout on the SDO pin of
the previous sample. CS transitioning low clocks out the
first leading zero and subsequent SCK falling edges clock
out the remaining data as shown in Figures 5, 6 and 7 for
three different timing schemes. Data is serially output MSB
first through LSB last, followed by trailing zeros if further
SCK falling edges are applied. Figure 5 illustrates that dur-
ing the case where SCK is held low during the acquisition
phase, only one leading zero is output. Figures 6 and 7
illustrate that for the SCK held high during acquisition or
continuous clocking mode two leading zeros are output.
Leading zeros allow the 12-bit data result to be framed
with both leading and trailing zeros for timing and data
verification. Since the rising edge of SCK will be coincident
with the falling edge of CS, delay t2 is the delay to the first
falling edge of SCK, which is simply 0.5 • tSCK. Delays t2
(CS falling edge to SCK leading edge) and t10 (14th falling
SCK edge to CS rising edge) must be observed for Figures
5, 6 and 7 and any timing implementation in order for the
conversion process and data readout to occur correctly.
The user can bring CS high after the 14th falling SCK edge
provided that timing delay t10 is observed. Prematurely
terminating the conversion by bringing CS high before
the 14th falling SCK edge plus delay t10 will cause a loss
of conversion data for that sample. The sample-and-hold
is placed in sample mode when CS is brought high. As
shown in Figure 6, a sample rate of 5Msps can be achieved
on the LTC2315-12 by using an 87.5MHz SCK data clock
and a minimum acquisition time of 40ns which results in
the minimum throughput time (tTHROUGHPUT) of 200ns.
Note that the maximum throughput of 5Msps can only be
achieved with the timing implementation of SCK held high
during acquisition as shown in Figure 6.
The LTC2315-12 also supports a continuous data clock
as shown in Figure 7. With a continuous data clock the
acquisition time period and conversion time period must
be designed as an exact integer number of data clock
periods. Because the minimum acquisition time is not an
exact multiple of the minimum SCK period, the maximum
sample rate for the continuous SCK timing is less than
5Msps. For example, a 4.86Msps throughput is achieved
using exactly 18 data clock periods with the maximum data
clock frequency of 87.5MHz. For this particular case, the
acquisition time period and conversion clock period are
designed as 4 data clock periods (TACQ = 45.7ns) and 14
data clock periods (TCONV = 160ns) respectively, yielding
a throughput time of 205.7ns.
LTc2315—1 2
LTC2315-12
12
231512fa
For more information www.linear.com/LTC2315-12
APPLICATIONS INFORMATION
The following table illustrates the maximum throughput
achievable for each of the three timing patterns. Note
that in order to achieve the maximum throughput rate of
5Msps, the timing pattern where SCK is held high during
the acquisition time must be used.
Table 1: Maximum Throughput vs Timing Pattern
TIMING PATTERN MAXIMUM
THROUGHPUT
SCK high during TACQ 5Msps
SCK low during TACQ 4.86Msps
SCK continuous (tTHROUGHPUT = 18 periods) 4.86Msps
Serial Data Output (SDO)
The SDO output is always forced into the high impedance
state while CS is high. The falling edge of CS starts the
conversion and enables SDO. The A/D conversion result
is shifted out on the SDO pin as a serial data stream with
the MSB first. The data stream consists of either one
leading zero (SCK held low during acquisition, Fig. 5) or
two leading zeros (SCK held high during acquisition, Fig.
6) followed by 12 bits of conversion data. There is 1 cycle
of conversion latency. Subsequent falling SCK edges after
the LSB is output will output zeros on the SDO pin. The
SDO output returns to the high impedance state after the
16th falling edge of SCK.
The output swing on the SDO pin is controlled by the
OVDD pin voltage and supports a wide operating range
from 1.71V to 5.25V independent of the VDD pin voltage.
Power Considerations
The LTC2315-12 provides two sets of power supply pins:
the analog 5V power supply (VDD) and the digital input/
output interface power supply (OVDD). The flexible OVDD
supply allows the LTC2315-12 to communicate with any
digital logic operating between 1.8V and 5V, including
2.5V and 3.3V systems.
Entering Nap/Sleep Mode
Pulsing CS two times and holding SCK static places the
LTC2315-12 into nap mode. Pulsing CS four times and
holding SCK static places the LTC2315-12 into sleep
mode. In sleep mode, all bias circuitry is shut down,
including the internal bandgap and reference buffer, and
only leakage currents remain (0.8µA typical). Because
the reference buffer is externally bypassed with a large
capacitor (2.2µF), the LTC2315-12 requires a significant
wait time (1.1ms) to recharge this capacitance before an
accurate conversion can be made. In contrast, nap mode
does not power down the internal bandgap or reference
buffer allowing for a fast wake-up and accurate conversion
within one conversion clock cycle. Supply current during
nap mode is nominally 1.8mA.
Exiting Nap/Sleep Mode
Waking up the LTC2315-12 from either nap or sleep mode,
as shown in Figures 8 and 9, requires SCK to be pulsed
one time. A conversion may be started immediately fol-
lowing nap mode as shown in Figure 8. A period of time
allowing the reference voltage to recover must follow
waking up from sleep mode as shown in Figure 9. The
wait period required before initiating a conversion for the
recommended value of CREF of 2.2µF is 1.1ms.
Power Supply Sequencing
The LTC2315-12 does not have any specific power sup-
ply sequencing requirements. Care should be taken to
observe the maximum voltage relationships described in
the Absolute Maximum Ratings section.
LTC231 5—1 2 00 erz STATE L7HEJWEGR 1 3
LTC2315-12
13
231512fa
For more information www.linear.com/LTC2315-12
Figure 8: LTC2315-12 Entering/Exiting Nap Mode
Figure 9: LTC2315-12 Entering/Exiting Sleep Mode
CS
SCK
Z
1 2
Z
SDO HI-Z STATE
231512 F08
NAP MODE
HOLD STATIC HIGH or LOW HOLD STATIC HIGH or LOW
START tACQ
0 0
CS
SCK
1 2
Z Z
3 4
SDO HI-Z STATE
231512 F09
NAP MODE SLEEP MODE
HOLD STATIC HIGH or LOW
START tACQ
VREF RECOVERY
0 0
tWAIT
APPLICATIONS INFORMATION
Single-Ended Analog Input Drive
The analog input of the LTC2315-12 is easy to drive. The
input draws only one small current spike while charging
the sample-and-hold capacitor at the end of conversion.
During the conversion, the analog input draws only a small
leakage current. If the source impedance of the driving
circuit is low, then the input of the LTC2315-12 can be
driven directly. As the source impedance increases, so
will the acquisition time. For minimum acquisition time
with high source impedance, a buffer amplifier should be
used. The main requirement is that the amplifier driving
the analog input must settle after the small current spike
before the next conversion starts. Settling time must be less
than tACQ-MIN (40ns) for full performance at the maximum
throughput rate. While choosing an input amplifier, also
keep in mind the amount of noise and harmonic distortion
the amplifier contributes.
Choosing an Input Amplifier
Choosing an input amplifier is easy if a few requirements
are taken into consideration. First, to limit the magnitude
of the voltage spike seen by the amplifier from charging
the sampling capacitor, choose an amplifier that has a low
output impedance (<50Ω) at the closed-loop bandwidth
frequency. For example, if an amplifier is used in a gain
of 1 and has a unity-gain bandwidth of 100MHz, then the
output impedance at 100MHz must be less than 50Ω. The
second requirement is that the closed-loop bandwidth
must be greater than 100MHz to ensure adequate small
signal settling for full throughput rate. If slower op amps
are used, more time for settling can be provided by in-
creasing the time between conversions. The best choice
for an op amp to drive the LTC2315-12 will depend on the
application. Generally, applications fall into two categories:
AC applications where dynamic specifications are most
LTc2315—1 2 ws._L LT‘B‘B T -I|-
LTC2315-12
14
231512fa
For more information www.linear.com/LTC2315-12
APPLICATIONS INFORMATION
critical and time domain applications where DC accuracy
and settling time are most critical. The following list is a
summary of the op amps that are suitable for driving the
LTC2315-12. (More detailed information is available on
the Linear Technology website at www.linear.com.)
LT6230: 215MHz GBWP, –80dBc Distortion at 1MHz,
Unity-Gain Stable, Rail-to-Rail Input and Output, 3.5mA/
Amplifier, 1.1nV/√Hz.
LT6200: 165MHz GBWP, –85dBc Distortion at 1MHz, Unity-
Gain Stable, R-R In and Out, 15mA/Amplifier, 0.95nV/√Hz.
LT1818/LT1819: 400MHz GBWP, –85dBc Distortion at
5MHz, Unity-Gain Stable, 9mA/Amplifier, Single/Dual
Voltage Mode Operational Amplifier.
Input Drive Circuits
The analog input of the LTC2315-12 is designed to be driven
single-ended with respect to GND. A low impedance source
can directly drive the high impedance analog input of the
LTC2315-12 without gain error. A high impedance source
should be buffered to minimize settling time during acquisi-
tion and to optimize the distortion performance of the ADC.
For best performance, a buffer amplifier should be used
to drive the analog input of the LTC2315-12. The amplifier
provides low output impedance to allow for fast settling
of the analog signal during the acquisition phase. It also
provides isolation between the signal source and the ADC
inputs which draw a small current spike during acquisition.
Input Filtering
The noise and distortion of the buffer amplifier and other
circuitry must be considered since they add to the ADC
noise and distortion. Noisy input circuitry should be filtered
prior to the analog inputs to minimize noise. A simple
1-pole RC filter is sufficient for many applications.
Large filter RC time constants slow down the settling at
the analog inputs. It is important that the overall RC time
constants be short enough to allow the analog inputs to
completely settle to >12-bit resolution within the minimum
acquisition time (tACQ-MIN) of 40ns.
A simple 1-pole RC filter is sufficient for many applica-
tions. For example, Figure 10 shows a recommended
single-ended buffered drive circuit using the LT1818 in
unity gain mode. The 47pF capacitor from AIN to ground
and 50Ω source resistor limits the input bandwidth to
68MHz. The 47pF capacitor also acts as a charge reservoir
for the input sample-and-hold and isolates the LT1818
from sampling glitch kick-back. The 50Ω source resistor
is used to help stabilize the settling response of the drive
amplifier. When choosing values of source resistance
and shunt capacitance, the drive amplifier data sheet
should be consulted and followed for optimum settling
response. If lower input bandwidths are desired, care
should be taken to optimize the settling response of the
driver amplifier with higher values of shunt capacitance
or series resistance. High quality capacitors and resistors
should be used in the RC filter since these components
can add distortion. NP0/C0G 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. When high amplitude unwanted signals are close
in frequency to the desired signal frequency, a multiple
pole filter is required. High external source resistance,
combined with external shunt capacitance at Pin 4 and
13pF of input capacitance on the LTC2315-12 in sample
mode, will significantly reduce the internal 130MHz input
bandwidth and may increase the required acquisition time
beyond the minimum acquisition time (tACQ-MIN) of 40ns.
47pF
50Ω
2315112 F10
AIN
LTC2315-12
LT1818 GND
ANALOG IN +
Figure 10. RC Input Filter
LTC231 5—1 2 L7HEJWEGR 1 5
LTC2315-12
15
231512fa
For more information www.linear.com/LTC2315-12
Figure 11. LTC2315-12 Transfer Function
INPUT VOLTAGE (V)
OUTPUT CODE
231512 F11
111...111
111...110
000...000
000...001
FS – 1LSB0 1LSB
APPLICATIONS INFORMATION
ADC Reference
A low noise, low temperature drift reference is critical to
achieving the full data sheet performance of the ADC. The
LTC2315-12 provides an excellent internal reference with
a guaranteed 20ppm/°C maximum temperature coefficient.
For added flexibility, an external reference may also be used.
The high speed, low noise internal reference buffer is used
only in the internal reference configuration. The reference
buffer must be overdriven in the external reference con-
figuration with a voltage 50mV higher than the nominal
reference output voltage in the internal configuration.
Using the Internal Reference
The internal bandgap and reference buffer are active by
default when the LTC2315-12 is not in sleep mode. The
reference voltage at the REF pin scales automatically with
the supply voltage at the VDD pin. The scaling of the refer-
ence voltage with supply is shown in the following table.
Table 2: Reference Voltage vs Supply Range
SUPPLY VOLTAGE (VDD) REF VOLTAGE (VREF)
2.7V –> 3.6V 2.048V
4.75V –> 5.25V 4.096V
The reference voltage also determines the full-scale analog
input range of the LTC2315-12. For example, a 2.048V
reference voltage will accommodate an analog input range
from 0V to 2.048V. An analog input voltage that goes below
0V will be coded as all zeros and an analog input voltage
that exceeds 2.048V will be coded as all ones.
It is recommended that the REF pin be bypassed to ground
with a low ESR, 2.2µF ceramic chip capacitor for optimum
performance.
External Reference
An external reference can be used with the LTC2315-12
if better performance is required or to accommodate a
larger input voltage span. The only constraints are that
the external reference voltage must be 50mV higher than
the internal reference voltage (see Table 2) and must be
less than or equal to the supply voltage (or 4.3V for the 5V
supply range). For example, a 3.3V external reference may
be used with a 3.3V VDD supply voltage to provide a 3.3V
analog input voltage span (i.e. 3.3V > 2.048V + 50mV).
Or alternatively, a 2.5V reference may be used with a 3V
supply voltage to provide a 2.5V input voltage range (i.e.
2.5V > 2.048V + 50mV). The LTC6655-3.3, LTC6655-2.5,
available from Linear Technology, may be suitable for
many applications requiring a high performance external
reference for either 3.3V or 2.5V input spans respectively.
Transfer Function
Figure 11 depicts the transfer function of the LTC2315-12.
The code transitions occur midway between successive
integer LSB values (i.e. 0.5LSB, 1.5LSB, 2.5LSB… FS-
0.5LSB). The output code is straight binary with 1LSB =
VREF/4,096.
DC Performance
The noise of an ADC can be evaluated in two ways: signal-to-
noise ratio (SNR) in the frequency domain and histogram in
the time domain. The LTC2315-12 excels in both. The noise in
the time domain histogram is the transition noise associated
LTC2315—1 2 V1
LTC2315-12
16
231512fa
For more information www.linear.com/LTC2315-12
APPLICATIONS INFORMATION
with a 12-bit resolution ADC which can be measured with a
fixed DC signal applied to the input of the ADC. The resulting
output codes are collected over a large number of conversions.
The shape of the distribution of codes will give an indication
of the magnitude of the transition noise. In Figure 12, the
distribution of output codes is shown for a DC input that has
been digitized 16,384 times. The distribution is Gaussian and
the RMS code transition noise is 0.33LSB. This corresponds to
a noise level of 73dB relative to a full scale voltage of 4.096V.
Figure 12. Histogram for 16384 Conversions
CODE
2047
COUNTS
2049
231512 F12
2048 2050 2051
σ = 0.33
0
10000
20000
30000
40000
60000
50000
Dynamic Performance
The LTC2315-12 has excellent high speed sampling
capability. 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 applied fundamental. The
LTC2315-12 provides guaranteed tested limits for both
AC distortion and noise measurements.
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 A/D output. The output is band-limited
to frequencies from above DC and below half the sampling
frequency. Figure 14 shows the LTC2315-12 maintains a
SINAD above 71dB up to the Nyquist input frequency of
2.5MHz.
Effective Number of Bits (ENOB)
The effective number of bits (ENOB) is a measurement of
the resolution of an ADC and is directly related to SINAD
by the equation where ENOB is the effective number of
bits of resolution and SINAD is expressed in dB:
ENOB = (SINAD – 1.76)/6.02
At the maximum sampling rate of 5MHz, the LTC2315-12
maintains an ENOB above 11.7 bits up to the Nyquist input
frequency of 2.5MHz. (Figure 14)
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 13 shows
that the LTC2315-12 achieves a typical SNR of 73dB at a
5MHz sampling rate with a 500kHz input frequency.
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+VN
2
V1
where V1 is the RMS amplitude of the fundamental fre-
quency and V2 through VN are the amplitudes of the second
through Nth harmonics. THD versus Input Frequency is
shown in the Typical Performance Characteristics section.
The LTC2315-12 has excellent distortion performance up
to the Nyquist frequency.
Intermodulation Distortion (IMD)
If the ADC input signal consists of more than one spectral
component, the ADC transfer function nonlinearity can
produce intermodulation distortion (IMD) in addition to
THD. IMD is the change in one sinusoidal input caused
by the presence of another sinusoidal input at a different
frequency.
LTC231 5—1 2 L7HEJWEGR 1 7
LTC2315-12
17
231512fa
For more information www.linear.com/LTC2315-12
Figure 13. 16k Point FFT of the LTC2315-12 at fIN = 500 kHz
Figure 14. LTC2315-12 ENOB/SINAD vs fIN
Figure 15. LTC2315-12 IMD Plot
231512 F13
FREQUENCY (kHz)
AMPLITUDE (dBFS)
0 25002000
1000500 1500
0
–20
–40
–60
–80
–100
–120
–140
VDD = 5V
SNR = 73.1dBFS
SINAD = 72.6dBFS
THD = –84dB
SFDR = 87dBc
INPUT FREQUENCY (kHz)
0
69
70
SINAD (dBFS)
ENOB
71
72
73
74
11.2
11.3
11.5
11.7
11.8
12.0
500 1000 1500 2000 2500
231512 F14
VDD = 5V
VDD = 3V
INPUT FREQUENCY (kHz)
0
–160
–120
–140
MAGNITUDE (dB)
–80
–100
–60
–40
0
–20
500 1000 1500 2000 2500
231512 F15
VDD = 5V
fS = 5Msps
fa = 461.421kHz
fb = 541.421kHz
IMD2 (fb + fa) = –77.4dBc
IMD3 (2fb –fa) = –89.4dBc
APPLICATIONS INFORMATION
If two pure sine waves of frequencies fa and fb are ap-
plied to the ADC input, nonlinearities in the ADC transfer
function can create distortion products at the sum and
difference frequencies mfa ± n • fb , where m and n = 0,
1, 2, 3, etc. For example, the 2nd order IMD terms include
(fa ± fb). If the two input sine waves are equal in magnitude,
the value (in decibels) of the 2nd order IMD products can
be expressed by the following formula:
IMD(fa ± fb) = 20 • log[VA (fa ± fb)/VA (fa)]
The LTC2315-12 has excellent IMD as shown in Figure 15.
Spurious Free Dynamic Range (SFDR)
The spurious free dynamic range is the largest spectral
component excluding DC, the input signal and the harmon-
ics included in the THD. This value is expressed in decibels
relative to the RMS value of a full-scale input signal.
Full-Power and Full-Linear Bandwidth
The full-power bandwidth is the input frequency at which
the amplitude of the reconstructed fundamental is reduced
by 3dB for a full-scale input signal.
The full-linear bandwidth is the input frequency at which
the SINAD has dropped to 68dB (11 effective bits). The
LTC2315-12 has been designed to optimize the input
bandwidth, allowing the ADC to under-sample input signals
with frequencies above the converter’s Nyquist frequency.
The noise floor stays very low at high frequencies and
SINAD becomes dominated by distortion at frequencies
beyond Nyquist.
Recommended Layout
To obtain the best performance from the LTC2315-12 a
printed circuit board is required. Layout for the printed
circuit board (PCB) should ensure the digital and analog
signal lines are separated as much as possible. In particu-
lar, care should be taken not to run any digital clocks or
signals alongside analog signals or underneath the ADC.
The following is an example of a recommended PCB layout.
A single solid ground plane is used. Bypass capacitors to
the supplies are placed as close as possible to the supply
pins. Low impedance common returns for these bypass
capacitors are essential to the low noise operation of the
LTC2315—1 2 @uuu éuccm @m we: END 5%“ Enza‘m“ fig 3 I216? cg 1 J2 7 521* 7 _ '\ 1'17“ ’\ W15 “A L'L‘“ au-iauEH’ESEIfiEH-u ““I ‘Efi U7 5‘33 u“ ‘29 12 “LSTC23-CT88 ” - an HIGH SPEED sag am a “15:35 A 7 i 7 n H c . :2 m NE 8, U11 u mam: max 3 H , N I ll NE u ,_ :3 ”imam.” 3‘50“!) 2mg: CIRCUIT um: . 15636—- [l ”5 EEK ESL in“ R24: :R21 35 m ucssu ,5 Nat; «awn-19w mm" 18 L7 LJHE/‘R
LTC2315-12
18
231512fa
For more information www.linear.com/LTC2315-12
APPLICATIONS INFORMATION
Figure 16. Top Silkscreen
Figure 17. Layer 1 Top Layer
Figure 18. Layer 2 GND Plane
ADC. The analog input traces are screened by ground.
For more details and information refer to DC1563, the
evaluation kit for the LTC2315-12.
Bypassing Considerations
High quality tantalum and ceramic bypass capacitors
should be used at the VDD, OVDD and REF pins. For opti-
mum performance, a 2.2µF ceramic chip capacitor should
be used for the VDD and OVDD pins. The recommended
bypassing for the REF pin is also a low ESR, 2.2µF ceramic
capacitor. The traces connecting the pins and the bypass
capacitors must be kept as short as possible and should
be made as wide as possible avoiding the use of vias.
The following is an example of a recommended PCB layout.
All analog circuitry grounds should be terminated at the
LTC2315-12. The ground return from the LTC2315-12 to
the power supply should be low impedance for noise free
operation. Digital circuitry grounds must be connected to
the digital supply common.
In applications where the ADC data outputs and control
signals are connected to a continuously active micropro-
cessor bus, it is possible to get errors in the conversion
results. These errors are due to feed-through from the
microprocessor to the successive approximation com-
parator. The problem can be eliminated by forcing the
microprocessor into aWait” state during conversion or
by using three-state buffers to isolate the ADC data bus.
LTC231 5—1 2 %oa°o°oocoacgo o o o o L7Hfl§0g 1 9
LTC2315-12
19
231512fa
For more information www.linear.com/LTC2315-12
Figure 19. Layer 3 PWR Plane Figure 20. Layer 4 Bottom Layer
Figure 21. Partial DC1563 Demo Board Schematic
APPLICATIONS INFORMATION
4
9V TO 10V
U5
LT1790ACS6-2.048
1
1
AC
J4
DC
COUPLING
2 3
2
6
GND
GND
VDD REF
CSL
SCK
CSL
SCK
SDO SDO
OVDD
VI VO VCM VDD VCCIO
C8
10µF C9
4.7µF
C10
OPT
C11
OPT
C12
4.7µF
C7
OPT
REF
+
C6
4.7µF
R9
1k
C18
OPT
R18
1k
31.024V
2.048V
HD1X3-100
2
1
C17
F JP2
VCM
R14
0k
R15
49.9Ω
R16
33Ω
4
3231512 F21
1 2 5
8
7
6
U1
*
C19
47pF
NPO
JP1
HD1X3-100
AIN
0V TO 4.096V AIN
GND
LTC2315—1 2 M" fr fl + + W + J WII fl i 7? L 7 I L7LJ1‘JW
LTC2315-12
20
231512fa
For more information www.linear.com/LTC2315-12
PACKAGE DESCRIPTION
Please refer to http://www.linear.com/designtools/packaging/ for the most recent package drawings.
1.50 – 1.75
(NOTE 4)
2.80 BSC
0.22 – 0.36
8 PLCS (NOTE 3)
DATUM ‘A
0.09 – 0.20
(NOTE 3)
TS8 TSOT-23 0710 REV A
2.90 BSC
(NOTE 4)
0.65 BSC
1.95 BSC
0.80 – 0.90
1.00 MAX 0.01 – 0.10
0.20 BSC
0.30 – 0.50 REF
PIN ONE ID
NOTE:
1. DIMENSIONS ARE IN MILLIMETERS
2. DRAWING NOT TO SCALE
3. DIMENSIONS ARE INCLUSIVE OF PLATING
4. DIMENSIONS ARE EXCLUSIVE OF MOLD FLASH AND METAL BURR
5. MOLD FLASH SHALL NOT EXCEED 0.254mm
6. JEDEC PACKAGE REFERENCE IS MO-193
3.85 MAX
0.40
MAX
0.65
REF
RECOMMENDED SOLDER PAD LAYOUT
PER IPC CALCULATOR
1.4 MIN
2.62 REF
1.22 REF
TS8 Package
8-Lead Plastic TSOT-23
(Reference LTC DWG # 05-08-1637 Rev A)
LTC231 5—1 2 L7 LJUW 2 1
LTC2315-12
21
231512fa
For more information www.linear.com/LTC2315-12
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 representa-
tion that the interconnection of its circuits as described herein will not infringe on existing patent rights.
REVISION HISTORY
REV DATE DESCRIPTION PAGE NUMBER
A 10/13 Added pin-compatible family table
Changed TJMAX to 150°C
Changed SINAD condition for –3dB Input Linear Bandwidth to ≥68dB
Reordered/Renumbered Notes
1
2
3, 16
3, 4, 5
LTC2315—1 2 22 L7ELUEN2
LTC2315-12
22
231512fa
For more information www.linear.com/LTC2315-12
RELATED PARTS
TYPICAL APPLICATION
CONTROL
LOGIC
(FPGA, CPLD,
DSP, ETC.)
50Ω
1k
1k
0.1µF
VCC
VCC
NC7SVU04P5X
NL17SZ74
NC7SVUO4P5X
MASTER CLOCK
CONV ENABLE
D
PRE
CLR
CONV
Q
CS
SCK
SDO
>
LTC2315-12
33Ω 231512 TA03
Low-Jitter Clock Timing with RF Sine Generator Using Clock
Squaring/Level-Shifting Circuit and Re-Timing Flip-Flop
PART NUMBER DESCRIPTION COMMENTS
ADCs
LTC2313-12 12-Bit, 2.5Msps Serial ADC 3V/5V, 14mW/25mW, 20ppm/°C Max Internal Reference,
Single-Ended Input, 8-Lead TSOT-23 Package
LTC2312-12 12-Bit, 500ksps Serial ADC 3V/5V, 9mW/15mW, 20ppm/°C Max Internal Reference,
Single-Ended Input, 8-Lead TSOT-23 Package
LTC1403/LTC1403-1 12-Bit, 2.8Msps Serial ADC 3V, 14mW, Unipolar/Bipolar Inputs, MSOP Package
LTC1407/LTC1407-1 12-Bit, 3Msps Simultaneous Sampling ADC 3V, 2-Channel Differential, Unipolar/Bipolar Inputs, 14mW,
MSOP Package
LTC2355/LTC2356 12-/14-Bit, 3.5Msps Serial ADC 3.3V Supply, Differential, Input, 18mW, MSOP Package
LTC2365/LTC2366 12-Bit, 1Msps/3Msps Serial Sampling ADC 3.3V Supply, 8mW, TSOT-23 Package
Amplifiers
LT6236/LT6237 Single/Dual Operation Amplifier with Low
Wideband Noise
215MHz, 3.5mA/Amplifier, 1.1nV/√Hz
LT6200/LT6201 Single/Dual Operational Amplifiers 165MHz, 0.95nV/√Hz
LT6230/LT6231 Single/Dual Operational Amplifiers 215MHz, 3.5mA/Amplifier, 1.1nV/√Hz
LT1818/LT1819 Single/Dual Operational Amplifiers 400MHz, 9mA/Amplifier, 6nV/√Hz
References
LTC6655-2.5/LTC6655-3.3 Precision Low Drift Low Noise Buffered Reference 2.5V/3.3V, 5ppm/°C, 0.25ppm Peak-to-Peak Noise, MSOP-8 Package
LT1461-3/LT1461-3.3V Precision Series Voltage Family 0.05% Initial Accuracy, 3ppm Drift
Linear Technology Corporation
1630 McCarthy Blvd., Milpitas, CA 95035-7417
(408) 432-1900 FAX: (408) 434-0507 www.linear.com/LTC2315-12
LINEAR TECHNOLOGY CORPORATION 2013
LT 1013 REV A • PRINTED IN USA