ADS8318
SLAS568A – MAY 2008 – REVISED MARCH 2011
www.ti.com
16-BIT, 500-KSPS, SERIAL INTERFACE MICROPOWER, MINIATURE,
SAR ANALOG-TO-DIGITAL CONVERTER
Check for Samples: ADS8318
FEATURES
DESCRIPTION
•
•
•
•
•
The ADS8318 is a 16-bit, 500-KSPS analog-to-digital
converter. It operates with a 2.048-V to 5.5-V external
reference. The device includes a capacitor based,
SAR A/D converter with inherent sample and hold.
1
•
•
•
•
•
500-kHz Sample Rate
16-Bit Resolution
Zero Latency at Full Speed
Unipolar, Differential Input, Range: –Vref to Vref
SPI Compatible Serial Interface with Daisy
Chain Option
Excellent Performance:
– 95.2dB SNR Typ at 10-kHz I/P
– –108dB THD Typ at 10-kHz I/P
– ±1.0 LSB Max INL
– ±0.75 LSB Max DNL
Low Power Dissipation: 18 mW Typ at 500
KSPS
Power Scales Linearly with Speed: 3.6 mW/100
KSPS
Power Dissipation During Power-Down State:
0.25 μW Typ
10-Pin MSOP and SON Packages
The devices includes a 50-MHz SPI compatible serial
interface. The interface is designed to support daisy
chaining or cascading of multiple devices. Also a
Busy Indicator makes it easy to synchronize with the
digital host.
The ADS8318 unipolar differential input range
supports a differential input swing of –Vref to +Vref with
a common-mode of +Vref/2.
Device operation is optimized for very low power
operation, and the power consumption directly scales
with speed. This feature makes it attractive for lower
speed applications.
It is available in 10-pin MSOP and SON packages.
+VA
APPLICATIONS
•
•
•
•
•
Battery Powered Equipments
Data Acquisition Systems
Instrumentation and Process Control
Medical Electronics
Optical Networking
SAR
O/P
Drive
COMP
I/P
Shift
Reg
IN+
CDAC
+VBD
IN-
REFIN
Conversion and I/O
Control Logic
ADS8318
GND
SDO
SDI
SCLK
CONVST
1
Please be aware that an important notice concerning availability, standard warranty, and use in critical applications of Texas
Instruments semiconductor products and disclaimers thereto appears at the end of this data sheet.
PRODUCTION DATA information is current as of publication date.
Products conform to specifications per the terms of the Texas
Instruments standard warranty. Production processing does not
necessarily include testing of all parameters.
Copyright © 2008–2011, Texas Instruments Incorporated
ADS8318
SLAS568A – MAY 2008 – REVISED MARCH 2011
www.ti.com
This integrated circuit can be damaged by ESD. Texas Instruments recommends that all integrated circuits be handled with
appropriate precautions. Failure to observe proper handling and installation procedures can cause damage.
ESD damage can range from subtle performance degradation to complete device failure. Precision integrated circuits may be more
susceptible to damage because very small parametric changes could cause the device not to meet its published specifications.
ORDERING INFORMATION (1)
DEVICE
ADS8318I
MAXIMUM
INTEGRAL
LINEARITY
(LSB)
MAXIMUM
DIFFERENTIAL
LINEARITY
(LSB)
±1.5
NO MISSING
CODES AT
RESOLUTION
(BIT)
±1
PACKAGE
TYPE
PACKAGE
DESIGNATOR
10 Pin MSOP
DGS
10 Pin MSOP
±1.0
±0.75
ORDERING
INFORMATION
TRANSPORT
MEDIA
QUANTITY
ADS8318IDGST
250
ADS8318IDGSR
2500
CBC
DRC
ADS8318IDRCT
250
ADS8318IDRCR
2500
CBE
DGS
ADS8318IBDGST
250
ADS8318IBDGSR
2500
CBC
–40°C to 85°C
16
10 Pin SON
(1)
PACKAGE
MARKING
–40°C to 85°C
16
10 Pin SON
ADS8318IB
TEMPERATURE
RANGE
DRC
ADS8318IBDRCT
250
ADS8318IBDRCR
2500
CBE
For the most current specifications and ordering information, see the Package Option Addendum at the end of this document, or see the
TI website at www.ti.com.
ABSOLUTE MAXIMUM RATINGS
over operating free-air temperature range unless otherwise noted (1)
+IN
VALUE
UNIT
–0.3 to +VA + 0.3
V
±130
mA
–0.3 to +VA + 0.3
V
±130
mA
+VA to AGND
–0.3 to 7
V
+VBD to BDGND
–0.3 to 7
V
Digital input voltage to GND
–0.3 to +VBD + 0.3
V
Digital output to GND
–0.3 to +VBD + 0.3
V
–IN
TA
Operating free-air temperature range
–40 to 85
°C
Tstg
Storage temperature range
–65 to 150
°C
150
°C
Junction temperature (TJ max)
MSOP package
Maximum MSOP reflow temperature
SON package
Maximum SON reflow temperature
(1)
2
Power dissipation
θJA thermal impedance
(TJMax – TA)/θJA
°C
180
°C/W
ADS8318 is rated to MSL2 260°C per the
JSTD-020 specification
(TJMax – TA)/θJA
Power dissipation
θJA thermal impedance
70
°C/W
ADS8318 is rated to MSL2 260°C per the
JSTD-020 specification
Stresses beyond those listed under absolute maximum ratings may cause permanent damage to the device. These are stress ratings
only, and functional operation of the device at these or any other conditions beyond those indicated under recommended operating
conditions is not implied. Exposure to absolute-maximum-rated conditions for extended periods may affect device reliability.
Submit Documentation Feedback
Copyright © 2008–2011, Texas Instruments Incorporated
Product Folder Link(s): ADS8318
ADS8318
SLAS568A – MAY 2008 – REVISED MARCH 2011
www.ti.com
SPECIFICATIONS
TA = –40°C to 85°C, +VA = 5 V, +VBD = 5 V to 2.375 V, Vref = 4 V, fSAMPLE = 500 kHz (unless otherwise noted)
PARAMETER
TEST CONDITIONS
MIN
TYP
MAX
UNIT
ANALOG INPUT
Full-scale input span
(1)
Operating input range
+IN – (–IN)
–Vref
Vref
+IN
– 0.1
Vref + 0.1
–IN
– 0.1
Input common-mode range
0
Input capacitance
+IN and -IN terminal to GND
Input leakage current
During acquisition
V
Vref + 0.1
Vref/2
Vref/2+0.1
V
59
pF
1000
pA
16
Bits
SYSTEM PERFORMANCE
Resolution
No missing codes
16
ADS8318I
INL
Integral linearity (2)
DNL
Differential linearity
EO
Offset error (4)
EG
Gain error
CMRR
Common-mode rejection ratio
With common mode input signal = 200 mVp-p at 500
kHz
PSRR
Power supply rejection ratio
At FFF0h output code
ADS8318IB
ADS8318I
ADS8318IB
At 16-bit level
Bits
–1.5
±0.65
1.5
–1
±0.65
1
–1
±0.4
1
–0.75
±0.4
0.75
LSB (3)
LSB (3)
–1.5
±0.3
1.5
mV
–0.03
±0.003
0.03
%FSR
78
dB
80
Transition noise
dB
0.25
LSB
SAMPLING DYNAMICS
tCONV
Conversion time
Acquisition time
+VBD = 5 V
1400
+VBD = 3 V
1400
+VBD = 5 V
600
+VBD = 3 V
600
ns
Maximum throughput rate with or
without latency
0.5
Aperture delay
Aperture jitter, RMS
Step response
Overvoltage recovery
(1)
(2)
(3)
(4)
Settling to 16-bit accuracy
ns
MHz
2.5
ns
6
ps
600
ns
600
ns
Ideal input span, does not include gain or offset error.
This is endpoint INL, not best fit.
LSB means least significant bit
Measured relative to actual measured reference.
Submit Documentation Feedback
Copyright © 2008–2011, Texas Instruments Incorporated
Product Folder Link(s): ADS8318
3
ADS8318
SLAS568A – MAY 2008 – REVISED MARCH 2011
www.ti.com
SPECIFICATIONS (continued)
TA = –40°C to 85°C, +VA = 5 V, +VBD = 5 V to 2.375 V, Vref = 4 V, fSAMPLE = 500 kHz (unless otherwise noted)
PARAMETER
TEST CONDITIONS
MIN
TYP
MAX
UNIT
DYNAMIC CHARACTERISTICS
–114
VIN 0.4 dB below FS at 1 kHz, Vref = 5 V
THD
Total harmonic distortion
(5)
VIN 0.4 dB below FS at 10 kHz, Vref = 5 V
–108
VIN 0.4 dB below FS at 100 kHz, Vref = 5 V
–91.5
VIN 0.4 dB below FS at 1 kHz, Vref = 5 V
SNR
Signal-to-noise ratio
ADS8318IB
SINAD
SFDR
Signal-to-noise + distortion
Spurious free dynamic range
96
VIN 0.4 dB below FS at 10 kHz, Vref = 5 V
95.2
VIN 0.4 dB below FS at 100 kHz, Vref = 5 V
92.5
VIN 0.4 dB below FS at 1 kHz, Vref = 5 V
dB
dB
95.5
VIN 0.4 dB below FS at 1 kHz, Vref = 5 V
96
VIN 0.4 dB below FS at 10 kHz, Vref = 5 V
95
VIN 0.4 dB below FS at 100 kHz, Vref = 5 V
89.5
VIN 0.4 dB below FS at 1 kHz, Vref = 5 V
116
VIN 0.4 dB below FS at 10 kHz, Vref = 5 V
109
VIN 0.4 dB below FS at 100 kHz, Vref = 5 V
92
–3dB Small signal bandwidth
dB
dB
15
MHz
EXTERNAL REFERENCE INPUT
Vref
Input range
2.048
Reference input current
(6)
During conversion
4.096
VDD+0.1
V
μA
250
POWER SUPPLY REQUIREMENTS
Power supply
voltage
+VBD
Supply current
+VA
2.375
3.3
5.5
4.5
5
5.5
V
500-kHz Sample rate
3.6
4.5
mA
+VA
V
PVA
Power dissipation
+VA = 5 V, 500-kHz Sample rate
18
22.5
mW
IVApd
Device power-down current (7)
+VA = 5 V
50
300
nA
LOGIC FAMILY CMOS
VIH
IIH = 5 μA
+(0.7×VBD)
+VBD+0.3
V
VIL
IIL = 5 μA
–0.3
+(0.3×VBD)
V
IOH = 2 TTL loads
+VBD–0.3
+VBD
V
IOL = 2 TTL loads
0
0.4
V
–40
85
°C
VOH
Logic level
VOL
TEMPERATURE RANGE
TA
(5)
(6)
(7)
4
Operating free-air temperature
Calculated on the first nine harmonics of the input frequency
Can vary ±20%
Device automatically enters power-down state at the end of every conversion, and continues to be in power-down state as long as it is
in acquistion phase.
Submit Documentation Feedback
Copyright © 2008–2011, Texas Instruments Incorporated
Product Folder Link(s): ADS8318
ADS8318
SLAS568A – MAY 2008 – REVISED MARCH 2011
www.ti.com
TIMING REQUIREMENTS
All specifications typical at –40°C to 85°C, +VA = 5 V, +VBD ≥ 3.1 V
PARAMETER
REF FIGURE
MIN
TYP
MAX
UNIT
SAMPLING AND CONVERSION RELATED
tacq
Acquisition time
tcnv
Conversion time
tcyc
Time between conversions
t1
Pulse duration, CONVST high
t6
Pulse duration, CONVST low
600
Figure 46, Figure 48, Figure 50,
Figure 52
ns
1400
ns
2000
ns
Figure 46, Figure 48
10
ns
Figure 50, Figure 52, Figure 54
20
ns
20
ns
8
ns
8
ns
I/O RELATED
tclk
SCLK Period
tclkl
SCLK Low time
tclkh
SCLK High time
t2
SCLK Falling edge to data remains valid
t3
SCLK Falling edge to next data valid delay
ten
Enable time, CONVST or SDI Low to MSB valid
tdis
Disable time, CONVST or SDI high or last SCLK falling edge
to SDO 3-state (CS mode)
t4
Setup time, SDI valid to CONVST rising edge
t5
Hold time, SDI valid from CONVST rising edge
t7
Setup time, SCLK valid to CONVST rising edge
t8
Hold time, SCLK valid from CONVST rising edge
Figure 46, Figure 48, Figure 50,
Figure 52, Figure 54, Figure 56
5
ns
16
ns
Figure 46, Figure 50
15
ns
Figure 46, Figure 48, Figure 50,
Figure 52
12
ns
Figure 50, Figure 52
Figure 54
5
ns
5
ns
5
ns
5
ns
Submit Documentation Feedback
Copyright © 2008–2011, Texas Instruments Incorporated
Product Folder Link(s): ADS8318
5
ADS8318
SLAS568A – MAY 2008 – REVISED MARCH 2011
www.ti.com
TIMING REQUIREMENTS
All specifications typical at –40°C to 85°C, +VA = 5 V, +3.1 V > +VBD ≥ 2.375 V
PARAMETER
REF FIGURE
MIN
TYP
MAX
UNIT
SAMPLING AND CONVERSION RELATED
tacq
Acquisition time
tcnv
Conversion time
tcyc
Time between conversions
t1
Pulse width CONVST high
t6
Pulse width CONVST low
600
Figure 46, Figure 48, Figure 50,
Figure 52
ns
1400
ns
2000
ns
Figure 46, Figure 48
10
ns
Figure 50, Figure 52, Figure 54
20
ns
I/O RELATED
tclk
SCLK period
30
ns
tclkl
SCLK low time
13
ns
tclkh
SCLK high time
13
ns
t2
SCLK falling edge to data remains valid
t3
SCLK falling edge to next data valid delay
ten
CONVST or SDI low to MSB valid
tdis
CONVST or SDI high or last SCLK falling edge to SDO
3-state (CS mode)
t4
SDI valid setup time to CONVST rising edge
t5
SDI valid hold time from CONVST rising edge
t7
SCLK valid setup time to CONVST rising edge
t8
SCLK valid hold time from CONVST rising edge
Figure 46, Figure 48, Figure 50,
Figure 52, Figure 54, Figure 56
5
ns
Figure 46, Figure 50
22
ns
Figure 46, Figure 48, Figure 50,
Figure 52
15
ns
Figure 50, Figure 52
Figure 54
500µA
ns
24
5
ns
5
ns
5
ns
5
ns
I ol
From
SDO
1.4V
20pF
500µA
I oh
Figure 1. Load Circuit for Digital Interface Timing
0.7 VBD
0.3 VBD
t DELAY
tDELAY
2V
2V
0.8V
0.8V
Figure 2. Voltage Levels for Timing
6
Submit Documentation Feedback
Copyright © 2008–2011, Texas Instruments Incorporated
Product Folder Link(s): ADS8318
ADS8318
SLAS568A – MAY 2008 – REVISED MARCH 2011
www.ti.com
PIN ASSIGNMENTS
MSOP PACKAGE
(TOP VIEW)
REFIN
+VA
IN+
INGND
1
10
2
9
3
8
4
7
5
6
SON PACKAGE
(TOP VIEW)
+VBD
SDI
SCLK
SDO
CONVST
REFIN
+VA
IN+
INGND
1
10
2
9
3
8
4
7
5
6
+VBD
SDI
SCLK
SDO
CONVST
Terminal Functions
TERMINAL
NO.
I/O
NAME
DESCRIPTION
ANALOG PINS
1
REFIN
I
Reference (positive) input. Decouple with GND pin using 0.1-μF bypass capacitor and 10-μF storage
capacitor.
3
+IN
I
Noninverting analog signal input
4
–IN
I
Inverting analog signal input
6
CONVST
I
Convert input. It also functions as the CS input in 3-wire interface mode. Refer to Description and Timing
Diagrams sections for more details.
7
SDO
O
Serial data output.
8
SCLK
I
Serial I/O clock input. Data (on SDO o/p) is synchronized with this clock.
9
SDI
I
Serial data input. The SDI level at the start of a conversion selects the mode of operation such as CS or daisy
chain mode. It also serves as the CS input in 4-wire interface mode. Refer to Description and Timing
Diagrmas sections for more details.
I/O PINS
POWER SUPPLY PINS
2
+VA
–
Analog power supply. Decoupled with GND pin.
5
GND
–
Device ground. Note this is a common ground pin for both analog power supply (+VA) and digital I/O supply
(+VBD).
10
+VBD
–
Digital I/O power supply. Decouple with GND pin.
TYPICAL CHARACTERISTICS
OFFSET ERROR
vs
SUPPLY VOLTAGE
GAIN ERROR
vs
SUPPLY VOLTAGE
-0.001
0.4
0.32
0.3
0.28
0.26
-0.004
-0.005
-0.006
-0.007
0.24
-0.008
0.22
-0.009
4.75
5
5.25
+VA - Supply Voltage - V
0.3
-0.003
0.34
0.2
4.5
0.35
-0.002
5.5
Figure 3.
Offset Error - mV
Offset Error - mV
0.36
+VBD = 2.7 V,
Vref = 4.096 V,
fs = 500 KSPS,
TA = 30°C
Gain Error - %FSR
0.38
OFFSET ERROR
vs
REFERENCE VOLTAGE
-0.01
4.5
0.25
0.2
0.15
+VA = 5 V
+VBD = 2.7 V,
fs = 500 KSPS,
TA = 30°C
0.1
+VBD = 2.7 V,
Vref = 4.096 V,
fs = 500 KSPS,
TA = 30°C
0.05
0
4.75
5
5.25
+VA - Supply Voltage - V
Figure 4.
5.5
2
2.5
3
3.5
4
4.5
Vref - Reference Voltage - V
Figure 5.
Submit Documentation Feedback
Copyright © 2008–2011, Texas Instruments Incorporated
Product Folder Link(s): ADS8318
5
7
ADS8318
SLAS568A – MAY 2008 – REVISED MARCH 2011
www.ti.com
TYPICAL CHARACTERISTICS (continued)
GAIN ERROR
vs
REFERENCE VOLTAGE
OFFSET ERROR
vs
FREE-AIR TEMPERATURE
-0.001
1
-0.002
0.9
-0.006
-0.007
+VA = 5 V
+VBD = 2.7 V,
fs = 500 KSPS,
TA = 30°C
-0.008
-0.009
-0.01
2
0
0.7
Gain Error - %FSR
Offset Error - mV
-0.005
0.6
0.5
0.4
0.3
0.2
2.5
3
3.5
4
4.5
Vref - Reference Voltage - V
-0.006
-0.008
0
-40
5
-25 -10
5
20
35 50 65
TA - Free-Air Temperature - °C
-0.01
-40 -25
80
-10
5
20 35
50 65
TA - Free-Air Temperature - °C
80
Figure 8.
GAIN ERROR DRIFT HISTOGRAM
OFFSET ERROR DRIFT
HISTOGRAM
DIFFERENTIAL NONLINEARITY
vs
SUPPLY VOLTAGE
16
10
9
8
8
8
6
1
19
+VA = 5 V
+VBD = 2.7 V,
Vref = 5 V,
fs = 500 KSPS
18
DNL - Differential Nonlinearity - LSBs
12
20
15
+VA = 5 V
+VBD = 2.7 V,
Vref = 5 V,
fs = 500 KSPS,
TA = 30°C
17
14
12
10
8
6
4
4
2
0
0
0
0
0
0
2
2
1
0
0
0
1
0
1
0
0
0
1
0.8
0.6
+VBD = 2.7 V,
Vref = 4.096 V,
fs = 500 KSPS,
TA = 30°C
DNLMAX
0.4
0.2
0
-0.2
DNLMIN
-0.4
-0.6
-0.8
-1
4.5
-0.5-0.4-0.3-0.2 -0.1 0 0.1 0.2 0.3 0.4 0.5 0.6
ppm/°C
-0.5 -0.4 -0.3-0.2-0.1 0 0.1 0.2 0.3 0.4 0.5
ppm/°C
Figure 9.
Figure 10.
Figure 11.
INTEGRAL NONLINEARITY
vs
SUPPLY VOLTAGE
DIFFERENTIAL NONLINEARITY
vs
REFERENCE VOLTAGE
INTEGRAL NONLINEARITY
vs
REFERENCE VOLTAGE
1
0.8
0.6
INLMAX
0.4
0.2
+VBD = 2.7 V,
Vref = 4.096 V,
fs = 500 KSPS,
TA = 30°C
0
-0.2
-0.4
INLMIN
-0.6
-0.8
-1
0.6
DNLMAX
0.4
+VA = 5 V
+VBD = 2.7 V,
fs = 500 KSPS,
TA = 30°C
0.2
0
-0.2
-0.4
DNLMIN
-0.6
-0.8
-1
4.5
4.75
5
5.25
+VA - Supply Voltage - V
Figure 12.
5.5
4.75
5
5.25
+VA - Supply Voltage - V
5.5
1
INL - Integral Nonlinearity - LSBs
1
0.8
DNL - Differential Nonlinearity - LSBs
INL - Integral Nonlinearity - LSBs
-0.004
Figure 7.
14
8
-0.002
Figure 6.
16
0
+VA = 5 V
+VBD = 2.7 V,
Vref = 5 V,
fs = 500 KSPS
0.1
Number of Devices
Gain Error - %FSR
-0.004
Number of Devices
0.002
+VA = 5 V
+VBD = 2.7 V,
Vref = 5 V,
fs = 500 KSPS
0.8
-0.003
GAIN ERROR
vs
FREE-AIR TEMPERATURE
2
2.5
3
3.5
4
4.5
Vref - Reference Voltage - V
Figure 13.
Submit Documentation Feedback
5
0.8
INLMAX
0.6
0.4
0.2
+VA = 5 V
+VBD = 2.7 V,
fs = 500 KSPS,
TA = 30°C
0
-0.2
-0.4
INLMIN
-0.6
-0.8
2
2.5
3
3.5
4
4.5
Vref - Reference Voltage - V
5
Figure 14.
Copyright © 2008–2011, Texas Instruments Incorporated
Product Folder Link(s): ADS8318
ADS8318
SLAS568A – MAY 2008 – REVISED MARCH 2011
www.ti.com
TYPICAL CHARACTERISTICS (continued)
DIFFERENTIAL NONLINEARITY
vs
FREE-AIR TEMPERATURE
INTEGRAL NONLINEARITY
vs
FREE-AIR TEMPERATURE
0.8
DNLMAX
0.4
0.2
0
-0.2
ENOB - Effective Number Of Bits - LSBs
0.6
DNLMIN
-0.4
-0.6
-0.8
INLMAX
0.6
0.4
+VA = 5 V
+VBD = 2.7 V,
Vref = 5 V,
fs = 500 KSPS
0.2
0
-0.2
-0.4
INLMIN
-0.6
-0.8
-1
-40 -25
-10 5
20 35 50 65
TA - Free-Air Temperature - °C
-1
-40
80
-25 -10
5
20 35 50
65
TA - Free-Air Temperature - °C
+VBD = 2.7 V,
Vref = 4.096 V,
fs = 500 KSPS,
fi = 1.9 kHz
TA = 30°C
15.9
15.8
15.7
15.6
15.5
15.4
15.3
15.2
15.1
15
4.5
80
4.75
5
5.25
+VA - Supply Voltage - V
5.5
Figure 15.
Figure 16.
Figure 17.
EFFECTIVE NUMBER OF BITS
vs
REFERENCE VOLTAGE
EFFECTIVE NUMBER OF BITS
vs
FREE-AIR TEMPERATURE
SPURIOUS FREE DYNAMIC RANGE
vs
SUPPLY VOLTAGE
15.8
15.7
ENOB - Effective Number Of Bits - LSBs
+VA = 5 V
+VBD = 2.7 V,
fs = 500 KSPS,
fi = 1.9 kHz,
TA = 30°C
15.9
15.6
15.5
15.4
15.3
15.2
15.1
2.5
3
3.5
4
4.5
Vref - Reference Voltage - V
15.8
15.7
5
122
+VA = 5 V,
+VBD = 2.7 V,
Vref = 5 V,
fs = 500 KSPS,
fi = 1.9 kHz
15.6
15.5
15.4
15.3
15.2
15.1
15
-40 -25 -10
5
20 35 50 65
TA - Free-Air Temperature - °C
15
2
15.9
Spurious Free Dynamic Range - dB
16
16
ENOB - Effective Number Of Bits - LSBs
16
1
+VA = 5 V
+VBD = 2.7 V,
Vref = 5 V,
fs = 500 KSPS
0.8
INL - Integral Nonlinearity - LSBs
DNL - Differential Nonlinearity - LSBs
1
EFFECTIVE NUMBER OF BITS
vs
SUPPLY VOLTAGE
121
120
119
118
117
+VBD = 2.7 V,
Vref = 4.096 V,
fs = 500 KSPS,
fi = 1.9 kHz
TA = 30°C
116
115
114
4.5
80
4.75
5
5.25
+VA - Supply Voltage - V
5.5
Figure 18.
Figure 19.
Figure 20.
SIGNAL-TO-NOISE + DISTORTION
vs
SUPPLY VOLTAGE
SIGNAL-TO-NOISE RATIO
vs
SUPPLY VOLTAGE
TOTAL HARMONIC DISTORTION
vs
SUPPLY VOLTAGE
96.4
96.2
96.2
96
95.8
95.6
+VBD = 2.7 V,
95.4 Vref = 4.096 V,
fs = 500 KSPS,
95.2 fi = 1.9 kHz
TA = 30°C
95
4.5
4.75
5
5.25
+VA - Supply Voltage - V
5.5
Figure 21.
Total Harmonic Distortion - dB
121
Signal-to-Noise Ratio - dB
Signal-to-Noise + Distortion - dB
122
96.4
96
95.8
95.6
+VBD = 2.7 V,
95.4 Vref = 4.096 V,
fs = 500 KSPS,
95.2 fi = 1.9 kHz
TA = 30°C
95
4.5
4.75
5
5.25
+VA - Supply Voltage - V
Figure 22.
5.5
120
119
118
117
116
115
+VBD = 2.7 V,
Vref = 4.096 V,
fs = 500 KSPS,
fi = 1.9 kHz
TA = 30°C
114
4.5
4.75
5
5.25
+VA - Supply Voltage - V
Figure 23.
Submit Documentation Feedback
Copyright © 2008–2011, Texas Instruments Incorporated
Product Folder Link(s): ADS8318
5.5
9
ADS8318
SLAS568A – MAY 2008 – REVISED MARCH 2011
www.ti.com
TYPICAL CHARACTERISTICS (continued)
SPURIOUS FREE DYNAMIC RANGE
vs
REFERENCE VOLTAGE
SIGNAL-TO-NOISE + DISTORTION
vs
REFERENCE VOLTAGE
121
+VA = 5 V
+VBD = 2.7 V,
fs = 500 KSPS,
fi = 1.9 kHz,
TA = 30°C
120
119
118
117
116
96
95.5
+VA = 5 V
+VBD = 2.7 V,
fs = 500 KSPS,
fi = 1.9 kHz,
TA = 30°C
95
94.5
94
95.5
+VA = 5 V
+VBD = 2.7 V,
fs = 500 KSPS,
fi = 1.9 kHz,
TA = 30°C
95
94.5
94
93.5
93.5
2.5
3
3.5
4
4.5
Vref - Reference Voltage - V
5
2
2.5
3
3.5
4
4.5
Vref - Reference Voltage - V
2
5
2.5
3
3.5
4
4.5
Vref - Reference Voltage - V
5
Figure 24.
Figure 25.
Figure 26.
TOTAL HARMONIC DISTORTION
vs
REFERENCE VOLTAGE
SPURIOUS FREE DYNAMIC RANGE
vs
FREE-AIR TEMPERATURE
SIGNAL-TO-NOISE + DISTORTION
vs
FREE-AIR TEMPERATURE
123
122
121
+VA = 5 V
+VBD = 2.7 V,
fs = 500 KSPS,
fi = 1.9 kHz,
TA = 30°C
120
119
118
117
116
115
96.4
117
116.5
116
115.5
115
+VA = 5 V,
+VBD = 2.7 V,
Vref = 5 V,
fs = 500 KSPS,
fi = 1.9 kHz
114.5
114
5
-10 5
20 35 50
65
TA - Free-Air Temperature - °C
96.3
96.2
96.1
96
95.9
+VA = 5 V,
+VBD = 2.7 V,
Vref = 5 V,
fs = 500 KSPS,
fi = 1.9 kHz
95.8
95.7
95.6
95.5
-40 -25
80
-10 5
20 35 50
65
TA - Free-Air Temperature - °C
80
Figure 27.
Figure 28.
Figure 29.
SIGNAL-TO-NOISE RATIO
vs
FREE-AIR TEMPERATURE
TOTAL HARMONIC DISTORTION
vs
FREE-AIR TEMPERATURE
TOTAL HARMONIC DISTORTION
vs
INPUT FREQUENCY
120
118
SNR
96.4
96.3
96.2
96.1
96
95.9
95.8
95.7
95.6
95.5
-40 -25
+VA = 5 V,
+VBD = 2.7 V,
Vref = 5 V,
fs = 500 KSPS,
fi = 1.9 kHz
-10 5
20 35 50
65
TA - Free-Air Temperature - °C
80
Figure 30.
Total Harmonic Distortion - dB
117.5
117
116.5
116
115.5
115
114.5
114
113.5
-40 -25
+VA = 5 V,
+VBD = 2.7 V,
Vref = 5 V,
fs = 500 KSPS,
fi = 1.9 kHz
THD - Total Harmonic Distortion - dB
96.5
2.5
3
3.5
4
4.5
Vref - Reference Voltage - V
96.5
113.5
-40 -25
114
2
118
117.5
Signal-to-Noise + Distortion - dB
Spurious Free Dynamic Range - dB
124
Total Harmonic Distortion - dB
96
115
2
Signal-to-Noise Ratio - dB
96.5
Signal-to-Noise Ratio - dB
122
114
10
96.5
123
Signal-to-Noise + Distortion - dB
Spurious Free Dynamic Range - dB
124
SIGNAL-TO-NOISE RATIO
vs
REFERENCE VOLTAGE
115
110
105
100
THD @ -0.5 dB
95
Figure 31.
Submit Documentation Feedback
80
+VA = 5 V
+VBD = 2.7 V,
Vref = 5 V,
fs = 500 KSPS,
TA = 30°C
90
85
80
-10 5
20 35 50
65
TA - Free-Air Temperature - °C
THD @ -10 dB
1
10
fi - Input frequency - kHz
100
Figure 32.
Copyright © 2008–2011, Texas Instruments Incorporated
Product Folder Link(s): ADS8318
ADS8318
SLAS568A – MAY 2008 – REVISED MARCH 2011
www.ti.com
TYPICAL CHARACTERISTICS (continued)
SINAD @ -10 dB
97
200000
95
SINAD @ -0.5 dB
+VA = 5 V,
+VBD = 2.7 V,
Vref = 5 V,
fs = 500 KSPS,
TA = 30°C
150000
93
91
100000
+VA = 5 V
+VBD = 2.7 V,
Vref = 5 V,
fs = 500 KSPS,
TA = 30°C
89
87
46104
50000
0
85
THD - Total Harmonic Distortion - dB
216040
0
10
fi - Input frequency - kHz
100
32757
111
0
32760
100
200
300
400
Source Resistance - W
500
SUPPLY CURRENT
vs
SAMPLING FREQUENCY
4
4.2
4
+VA = 5 V,
+VBD = 2.7 V,
Vref = 5 V,
fs = 500 KSPS
3.8
3.6
3.4
3.2
3
-40 -25
5.5
3
2.5
2
1.5
1
0.5
3.35
4.75
5
5.25
+VA - Supply Voltage - V
+VA = 5 V,
+VBD = 2.7 V,
Vref = 5 V,
TA = 30°C
3.5
Iavdd - Supply Current - mA
+VBD = 2.7 V,
Vref = 4.096 V,
fs = 500 KSPS,
TA = 30°C
3.4
0
-10 5
20 35 50 65
TA - Free-Air Temperature - °C
0
80
50 100 150 200 250 300 350 400 450 500
fs - Sampling Frequency - KSPS
Figure 36.
Figure 37.
Figure 38.
POWER DISSIPATION
vs
SAMPLING FREQUENCY
POWERDOWN CURRENT
vs
SUPPLY VOLTAGE
POWERDOWN CURRENT
vs
FREE-AIR TEMPERATURE
500
Iavdd-pd - Powerdown Current - nA
+VA = 5 V,
+VBD = 2.7 V,
Vref = 5 V,
TA = 30°C
12
10
8
6
4
450
400
350
500
+VBD = 2.7 V,
Vref = 4.096 V,
fs = 0.0 KSPS,
TA = 30°C
Iavdd-pd - Powerdown Current - nA
20
300
250
200
150
100
50
2
0
0
+VA = 5 V,
+VBD = 2.7 V,
Vref = 5 V,
fs = 500 KSPS,
TA = 30°C
SUPPLY CURRENT
vs
FREE-AIR TEMPERATURE
3.5
14
680 pF
112
SUPPLY CURRENT
vs
SUPPLY VOLTAGE
3.45
16
113
Figure 35.
3.6
18
114
Figure 34.
3.55
3.3
4.5
115
Figure 33.
Iavdd - Supply Current - mA
3.7
3.65
32758
32759
Codes
0 pF
100 pF
116
110
0
1
3.8
Iavdd - Supply Current - mA
117
250000
99
3.75
Iavdd*VA - Power Dissipation - mW
TOTAL HARMONIC DISTORTION
vs
SOURCE RESISTANCE
DC HISTORAM OF ADC CLOSE TO
CENTER CODE
Hits
SINAD - Signal-to-Noise + Noise Distortion - dB
SIGNAL-TO-NOISE + DISTORTION
vs
INPUT FREQUENCY
50 100 150 200 250 300 350 400 450 500
fs - Sampling Frequency - KSPS
Figure 39.
0
4.5
450
400
+VA = 5 V,
+VBD = 2.7 V,
Vref = 5 V,
fs = 0.0 KSPS
350
300
250
200
150
100
50
4.75
5
5.25
+VA - Supply Voltage - V
Figure 40.
5.5
0
-40
-25
-10
5
20
35
50
65
Figure 41.
Submit Documentation Feedback
Copyright © 2008–2011, Texas Instruments Incorporated
Product Folder Link(s): ADS8318
80
TA - Free-Air Temperature - °C
11
ADS8318
SLAS568A – MAY 2008 – REVISED MARCH 2011
www.ti.com
TYPICAL CHARACTERISTICS (continued)
DNL
DNL - LSBs
1
0.8
+VA = 5 V, +VBD = 2.7 V,
Vref = 5 V, fs = 500 KSPS,
TA = 30°C
0.6
0.4
0.2
0
-0.2
-0.4
-0.6
-0.8
-1
0
10000
20000
30000
Codes
40000
50000
60000
Figure 42.
INL
1
+VA = 5 V, +VBD = 2.7 V,
Vref = 5 V, fs = 500 KSPS,
TA = 30°C
0.8
INL - LSBs
0.6
0.4
0.2
0
-0.2
-0.4
-0.6
-0.8
-1
0
10000
20000
30000
40000
Codes
50000
60000
Figure 43.
Amplitude - dB
FFT
0
-20
-40
-60
-80
-100
+VA = 5 V,
+VBD = 2.7 V,
Vref = 5 V,
fs = 500 KSPS,
fi = 1.9 kHz,
TA = 30C
-120
-140
-160
-180
-200
0
50
100
150
f - Frequency - kHz
200
250
Figure 44.
12
Submit Documentation Feedback
Copyright © 2008–2011, Texas Instruments Incorporated
Product Folder Link(s): ADS8318
ADS8318
SLAS568A – MAY 2008 – REVISED MARCH 2011
www.ti.com
DETAILED DESCRIPTIONS AND TIMING DIAGRAMS
The ADS8318 is a high-speed, low power, successive approximation register (SAR) analog-to-digital converter
(ADC) that uses an external reference. The architecture is based on charge redistribution, which inherently
includes a sample/hold function.
The ADS8318 is a single channel device. The analog input is provided to two input pins: +IN and -IN. When a
conversion is initiated, the differential input on these pins is sampled on the internal capacitor array. While a
conversion is in progress, both +IN and -IN inputs are disconnected from any internal function.
The ADS8318 has an internal clock that is used to run the conversion, and hence the conversion requires a fixed
amount of time. After a conversion is completed, the device reconnects the sampling capacitors to the +IN
and –IN pins, and the device is in the acquisition phase. During this phase the device is powered down and
conversion data can be read.
The device digital output is available in SPI compatible format. It easily interfaces with microprocessors, DSPs, or
FPGAs.
This is a low pin count device; however, it offers six different options for the interface. They can be grossly
classified as CS mode (3- or 4-wire interface) and daisy chain mode. In both modes it can either be with or
without a busy indicator, where the busy indicator is a bit preceeding the 16-bit serial data.
The 3-wire interface CS mode is useful for applications which need galvanic isolation on-board, where as 4-wire
interface CS mode makes it easy to control an individual device while having multiple devices on-board. The
daisy chain mode is provided to hook multiple devices in a chain like a shift register and is useful to reduce
component count and the number signal traces on the board.
CS MODE
CS Mode is selected if SDI is high at the rising edge of CONVST. As indicated before there are four different
interface options available in this mode, namely 3-wire CS mode without busy indicator, 3-wire CS mode with
busy indicator, 4-wire CS mode without busy indicator, 4-wire CS mode with busy indicator. The following section
discusses these interface options in detail.
3-Wire CS Mode Without Busy Indicator
Digital Host
ADS8318
+VBD
SDI
CONVST
CNV
SCLK
CLK
SDO
SDI
Figure 45. Connection Diagram, 3-Wire CS Mode without Busy Indicator (SDI = 1)
The three wire interface option in CS mode is selected if SDI is tied to +VBD (see Figure 45). In the three wire
interface option, CONVST acts like CS. As shown in Figure 46, the device samples the input signal and enters
the conversion phase on the rising edge of CONVST, at the same time SDO goes to 3-state. Conversion is done
with the internal clock and it continues irrespective of the state of CONVST. As a result it is possible to bring
CONVST (acting as CS) low after the start of the conversion to select other devices on the board. But it is
absolutely necessary that CONVST is high again before the minimum conversion time (tcnv in timing
requirements table) is elapsed. A high level on CONVST at the end of the conversion ensures the device does
not generate a busy indicator.
Submit Documentation Feedback
Copyright © 2008–2011, Texas Instruments Incorporated
Product Folder Link(s): ADS8318
13
ADS8318
SLAS568A – MAY 2008 – REVISED MARCH 2011
www.ti.com
When the conversion is over, the device enters the acquisition phase and powers down. On the falling edge of
CONVST, SDO comes out of three state, and the device outputs the MSB of the data. After this, the device
outputs the next lower data bits on every falling edge of SCLK. SDO goes to 3-state after the 16th falling edge of
SCLK or CONVST high, whichever occurs first. It is necessary that the device sees a minimum of 15 falling
edges of SCLK during the low period of CONVST.
tcyc
t1
CONVST
tacq
tcnv
ACQUISITION
CONVERSION
ACQUISITION
tclkl
t2
SCLK
1
2
ten
t3
SDO
D15
16
15
tclkh
tdis
tclk
D14
D1
D0
Figure 46. Interface Timing Diagram, 3 Wire CS Mode Without Busy Indicator (SDI = 1)
3 Wire CS Mode With Busy Indicator
Digital Host
ADS8318
CNV
CONVST
SDI
SCLK
+ VBD
SDO
CLK
SDI
IRQ
Figure 47. Connection Diagram, 3 Wire CS Mode With Busy Indicator
The three wire interface option in CS mode is selected if SDI is tied to +VBD (see Figure 47). In the three wire
interface option, CONVST acts like CS. As shown in Figure 48, the device samples the input signal and enters
the conversion phase on the rising edge of CONVST, at the same time SDO goes to 3 state. Conversion is done
with the internal clock and it continues irrespective of the state of CONVST. As a result it is possible to toggle
CONVST (acting as CS) after the start of the conversion to select other devices on the board. But it is absolutely
necessary that CONVST is low again before the minimum conversion time (tcnv in timing requirements table) is
elapsed and continues to stay low until the end of maximum conversion time. A low level on the CONVST input
at the end of a conversion ensures the device generates a busy indicator.
When the conversion is over, the device enters the acquisition phase and powers down, and the device forces
SDO out of three state and outputs a busy indicator bit (low level). The device outputs the MSB of data on the
first falling edge of SCLK after the conversion is over and continues to output the next lower data bits on every
subsequent falling edge of SCLK. SDO goes to three state after the 17th falling edge of SCLK or CONVST high,
whichever occurs first. It is necessary that the device sees a minimum of 16 falling edges of SCLK during the low
period of CONVST.
14
Submit Documentation Feedback
Copyright © 2008–2011, Texas Instruments Incorporated
Product Folder Link(s): ADS8318
ADS8318
SLAS568A – MAY 2008 – REVISED MARCH 2011
www.ti.com
tcyc
t1
CONVST
tacq
tcnv
ACQUISITION
CONVERSION
ACQUISITION
tclkl
t2
1
SCLK
2
3
16
t3
SDO
D15
tclk
D14
D1
17
tclkh
tdis
D0
Figure 48. Interface Timing Diagram, 3 Wire CS Mode With Busy Indicator (SDI = 1)
4 Wire CS Mode Without Busy Indicator
CS1
CS2
CNV
CONVST
SDI
CONVST
SDO
SCLK
SDI
SDO
SDI
SCLK
CLK
ADS8318#1
ADS8318#2
Digital Host
Figure 49. Connection Diagram, 4 Wire CS Mode Without Busy Indicator
As mentioned before for selecting CS mode it is necessary that SDI is high at the time of the CONVST rising
edge. Unlike in three wire interface option, SDI is controlled by digital host and acts like CS. As shown in
Figure 50, SDI goes to a high level before the rising edge of CONVST. The rising edge of CONVST while SDI is
high selects CS mode, forces SDO to three state, samples the input signal, and the device enters the conversion
phase. In the 4 wire interface option CONVST needs to be at a high level from the start of the conversion until all
of the data bits are read. Conversion is done with the internal clock and it continues irrespective of the state of
SDI. As a result it is possible to bring SDI (acting as CS) low to select other devices on the board. But it is
absolutely necessary that SDI is high again before the minimum conversion time (tcnv in timing requirements
table) is elapsed.
When the conversion is over, the device enters the acquisition phase and powers down. SDI falling edge can
occur after the maximum conversion time (tcnv in timing requirements table). Note that it is necessary that SDI is
high at the end of the conversion, so that the device does not generate a busy indicator. The falling edge of SDI
Submit Documentation Feedback
Copyright © 2008–2011, Texas Instruments Incorporated
Product Folder Link(s): ADS8318
15
ADS8318
SLAS568A – MAY 2008 – REVISED MARCH 2011
www.ti.com
brings SDO out of 3-state and the device outputs the MSB of the data. Subsequent to this the device outputs the
next lower data bits on every falling edge of SCLK. SDO goes to three state after the 16th falling edge of SCLK or
SDI (CS) high, whichever occurs first. As shown in Figure 49, it is possible to hook multiple devices on the same
data bus. In this case the second device SDI (acting as CS) can go low after the first device data is read and
device 1 SDO is in three state.
Care needs to be taken so that CONVST and SDI are not low together at any time during the cycle.
CONVST
t6
SDI (CS) #1
t4
t5
SDI (CS) #2
tcnv
ACQUISITION
tacq
CONVERSION
ten
ACQUISITION
tclkl
t2
SCLK
1
2
ten
t3
SDO
D15#1
D14#1
17
16
15
tclkh
tclk
D1#1
18
31
D0#1
32
tdis
tdis
D15#2 D14#2
D1#2
D0#2
Figure 50. Interface Timing Diagram, 4 Wire CS Mode Without Busy Indicator
4 Wire CS Mode With Busy Indicator
CS
SDI
CNV
CONVST
+ VBD
SDO
ADS8318
CLK
SDI
IRQ
Digital Host
Figure 51. Connection Diagram, 4 Wire CS Mode With Busy Indicator
As mentioned before for selecting CS mode it is necessary that SDI is high at the time of the CONVST rising
edge. Unlike in the three wire interface option, SDI is controlled by the digital host and acts like CS. As shown in
Figure 52, SDI goes to a high level before the rising edge of CONVST. The rising edge of CONVST while SDI is
high selects CS mode, forces SDO to three state, samples the input signal, and the device enters the conversion
phase. In the 4 wire interface option CONVST needs to be at a high level from the start of the conversion until all
of the data bits are read. Conversion is done with the internal clock and it continues irrespective of the state of
SDI. As a result it is possible to toggle SDI (acting as CS) to select other devices on the board. But it is
absolutely necessary that SDI is low before the minimum conversion time (tcnv in timing requirements table) is
elapsed and continues to stay low until the end of the maximum conversion time. A low level on the SDI input at
the end of a conversion ensures the device generates a busy indicator.
When the conversion is over, the device enters the acquisition phase and powers down, forces SDO out of three
state, and outputs a busy indicator bit (low level). The device outputs the MSB of the data on the first falling edge
of SCLK after the conversion is over and continues to output the next lower data bits on every falling edge of
SCLK. SDO goes to three state after the 17th falling edge of SCLK or SDI (CS) high, whichever occurs first.
16
Submit Documentation Feedback
Copyright © 2008–2011, Texas Instruments Incorporated
Product Folder Link(s): ADS8318
ADS8318
SLAS568A – MAY 2008 – REVISED MARCH 2011
www.ti.com
Care needs to be taken so that CONVST and SDI are not low together at any time during the cycle.
tcyc
t6
CNVST
t5
SDI (CS) t
4
tacq
tcnv
ACQUISITION
CONVERSION
ACQUISITION
tclkh
t2
1
SCLK
2
3
t3
SDO
D15
17
16
tclkl
tdis
tclk
D14
D1
D0
Figure 52. Interface Timing Diagram, 4 Wire CS Mode With Busy Indicator
Daisy Chain Mode
Daisy chain mode is selected if SDI is low at the time of CONVST rising edge. This mode is useful to reduce
wiring and hardware like digital isolators in the applications where multiple (ADC) devices are used. In this mode
all of the devices are connected in a chain (SDO of one device connected to the SDI of the next device) and data
transfer is analogous to a shift register.
Like CS mode even this mode offers operation with or without a busy indicator. The following section discusses
these interface options in detail.
Daisy Chain Mode Without Busy Indicator
CNV
CONVST
SDI
CONVST
SDO
SCLK
ADS8318#1
SDI
SDO
SDI
SCLK
ADS8318#2
CLK
Digital Host
Figure 53. Connection Diagram, Daisy Chain Mode Without Busy Indicator (SDI = 0)
Refer to Figure 53 for the connection diagram. SDI for device 1 is tied to ground and SDO of device 1 goes to
SDI of device 2 and so on. SDO of the last device in the chain goes to the digital host. CONVST for all of the
devices in the chain are tied together. In this mode there is no CS signal. The device SDO is driven low when
Submit Documentation Feedback
Copyright © 2008–2011, Texas Instruments Incorporated
Product Folder Link(s): ADS8318
17
ADS8318
SLAS568A – MAY 2008 – REVISED MARCH 2011
www.ti.com
SDI and CONVST are low together. The rising edge of CONVST while SDI is low selects daisy chain mode and
the device samples the analog input and enters the conversion phase. It is necessary that SCLK is low at the
rising edge of CONVST so that the device does not generate a busy indicator at the end of the conversion. In
this mode CONVST continues to be high from the start of the conversion until all of the data bits are read. Once
started, conversion continues irrespective of the state of SCLK.
At the end of the conversion, every device in the chain initiates output of its conversion data starting with the
MSB bit. Further the next lower data bit is output on every falling edge of SCLK. While every device outputs its
data on the SDO pin, it also receives previous device data on the SDI pin (other than device #1) and stores it in
the shift register. The device latches incoming data on every falling edge of SCLK. SDO of the first device in the
chain goes low after the 16th falling edge of SCLK. All subsequent devices in the chain output the stored data
from the previous device in MSB first format immediately following their own data word.
It needs 16 × N clocks to read data for N devices in the chain.
tcyc
t6
CONVST
tacq
tcnv
ACQUISITION
ACQUISITION
CONVERSION
t7
tclkl
t2
SCLK
1
2
16
15
t8
tclk
#1-D15
SDO #1, SDI #2
#1-D14
17
18
31
32
#2-D1
#2-D0
tclkh
#1-D1
#1-D0
#1-D1
#1-D0 #2-D15
t3
#1-D15
SDO #2
#1-D14
#2-D14
Figure 54. Interface Timing Diagram, Daisy Chain Mode Without Busy Indicator
Daisy Chain Mode With Busy Indicator
CNV
CONVST
SDI
CONVST
SDO
SCLK
ADS8318#1
SDI
IRQ
SDO
SDI
SCLK
ADS8318#2
CLK
Digital Host
Figure 55. Connection Diagram, Daisy Chain Mode With Busy Indicator (SDI = 0)
Refer to Figure 55 for the connection diagram. SDI for device 1 is wired to it's CONVST and CONVST for all the
devices in the chain are wired together. SDO of device 1 goes to SDI of device 2 and so on. SDO of the last
device in the chain goes to the digital host. In this mode there is no CS signal. On the rising edge of CONVST,
all of the device in the chain sample the analog input and enter the conversion phase. For the first device, SDI
18
Submit Documentation Feedback
Copyright © 2008–2011, Texas Instruments Incorporated
Product Folder Link(s): ADS8318
ADS8318
SLAS568A – MAY 2008 – REVISED MARCH 2011
www.ti.com
and CONVST are wired together, and the setup time of SDI to rising edge of CONVST is adjusted so that the
device still enters chain mode even though SDI and CONVST rise together. It is necessary that SCLK is high at
the rising edge of CONVST so that the device generates a busy indicator at the end of the conversion. In this
mode, CONVST continues to be high from the start of the conversion until all of the data bits are read. Once
started, conversion continues irrespective of the state of SCLK.
At the end of the conversion, all the devices in the chain generate busy indicators. On the first falling edge of
SCLK following the busy indicator bit, all of the devices in the chain output their conversion data starting with the
MSB bit. After this the next lower data bit is output on every falling edge of SCLK. While every device outputs its
data on the SDO pin, it also receives the previous device data on the SDI pin (except for device #1) and stores it
in the shift register. Each device latches incoming data on every falling edge of SCLK. SDO of the first device in
the chain goes high after the 17th falling edge of SCLK. All subsequent devices in the chain output the stored
data from the pervious device in MSB first format immediately following their own data word. It needs 16 × N + 1
clock pulses to read data for N devices in the chain.
tcyc
t6
CONVST
tacq
tcnv
ACQUISITION
ACQUISITION
CONVERSION
t7
tclkl
t2
1
SCLK
2
3
16
17
18
19
32
33
#2-D14
#2-D1
#2-D0
tclk
t8
tclkh
SDO #1, SDI #2
#1-D15
#1-D14
SDO #2
#1-D15
#1-D14
#1-D1
#1-D0
#1-D1
#1-D0 #2-D15
t3
Figure 56. Interface Timing Diagram, Daisy Chain Mode With Busy Indicator
Submit Documentation Feedback
Copyright © 2008–2011, Texas Instruments Incorporated
Product Folder Link(s): ADS8318
19
ADS8318
SLAS568A – MAY 2008 – REVISED MARCH 2011
www.ti.com
APPLICATION INFORMATION
ANALOG INPUT
When the converter samples the input, the voltage difference between the +IN and -IN inputs is captured on the
internal capacitor array. The voltage on the +IN and –IN inputs individually is limited between GND –0.1 V and
Vref + 0.1 V; where as the differential signal range [(+IN) – (–IN)] is 2Vref (–Vref to +Vref) with a common mode of
(Vref/2). This allows the input to reject small signals which are common to both the +IN and –IN inputs.
The (peak) input current through the analog inputs depends upon a number of factors: sample rate, input
voltage, and source impedance. The current into the ADS8318 charges the internal capacitor array during the
sample period. After this capacitance has been fully charged, there is no further input current. The source of the
analog input voltage must be able to charge the input capacitance (59 pF) to a 18-bit settling level within the
minimum acquisition time. When the converter goes into hold mode, the input impedance is greater than 1 GΩ.
Care must be taken regarding the absolute analog input voltage. To maintain linearity of the converter, the +IN
and -IN inputs and the span (+IN – (–IN)) should be within the limits specified. Outside of these ranges, converter
linearity may not meet specifications.
Care should be taken to ensure that the output impedance of the sources driving the +IN and –IN inputs are
matched. If this is not observed, the two inputs could have different settling times. This may result in an offset
error, gain error, and linearity error which change with temperature and input voltage.
Device in Hold Mode
218 W
+IN
55 pF
4 pF
+VA
AGND
4 pF
218 W
-IN
55 pF
Figure 57. Input Equivalent Circuit
DRIVER AMPLIFIER CHOICE
The analog input to the converter needs to be driven with a low noise, op-amp like the THS4031, OPA211. An
RC filter is recommended at the input pins to low-pass filter the noise from the source. Two resistors of 5Ω and a
differential capacitor of 1nF is recommended. The input to the converter is a unipolar input voltage in the range 0
V to Vref. The minimum –3dB bandwidth of the driving operational amplifier can be calculated as:
f3db = (ln(2) × (n+2))/(2π × tACQ)
where n is equal to 16, the resolution of the ADC (in the case of the ADS8318). When tACQ = 600 ns (minimum
acquisition time), the minimum bandwidth of the driving circuit is ~3 MHz (including RC following the driver OPA).
The bandwidth can be relaxed if the acquisition time is increased by the application.
Typically a low noise OPA with ten times or higher bandwidth is selected. The driving circuit bandwidth is
adjusted (to the required value) with a RC following the OPA. The OPA211 or THS4031 from Texas Instruments
is recommended for driving high-resolution high-speed ADCs.
DRIVER AMPLIFIER CONFIGURATIONS
Configuration for Unipolar Differential Input
It is better to use a unity gain, noninverting buffer configuration for a unipolar, differential input having a ±Vref
signal range with Vref/2 common-mode. As explained before a RC following the OPA limits the input circuit
bandwidth just enough for 16-bit settling. Note higher bandwidth reduces the settling time (beyond what is
needed) but increases the noise in the ADC sampled signal, and hence the ADC output.
20
Submit Documentation Feedback
Copyright © 2008–2011, Texas Instruments Incorporated
Product Folder Link(s): ADS8318
ADS8318
SLAS568A – MAY 2008 – REVISED MARCH 2011
www.ti.com
Figure 58. Unipolar Differential Input Drive Configuration
Configuration for Bipolar Single-Ended Input
The following circuit shows a way to convert a single-ended bipolar input to the unipolar differential input needed
for for converter. Note that the higher values of the resistors at the input of the top OPA may reduce power
consumption of the circuit but increase noise in the driving circuit. One can choose these components based on
application needs.
Vref
Bipolar
Analog
Input
± Vref
_
R
+
R
100 E
5E
+IN
1 nF
_ 100 E
Vref/2
-IN
5E
ADS8318
+
OPA Shown is THS4031 or OPA211
Figure 59. Bipolar Single-Ended Input Drive Configuration
REFERENCE
The ADS8318 can operate with an external reference with a range from 2.048 V to VDD + 0.1 V. A clean, low
noise, well-decoupled reference voltage on this pin is required to ensure good performance of the converter. A
low noise band-gap reference like the REF5050 can be used to drive this pin as shown in Figure 60 and
Figure 61. The capacitor should be placed as close as possible to the pins of the device.
Submit Documentation Feedback
Copyright © 2008–2011, Texas Instruments Incorporated
Product Folder Link(s): ADS8318
21
ADS8318
SLAS568A – MAY 2008 – REVISED MARCH 2011
www.ti.com
50 W
-
REF5050
OUT
TRIM
+
+
- 47 mF, OPA365
1.5 W ESR
(High ESR)
+
IN+
- 4.7 mF,
Low ESR
10 mF
REFIN
ADS8318
IN-
Figure 60. External Reference Driving Circuit
REF5050
OUT
+
-
47 mF,
1.5 W ESR
(High ESR)
22 mF
REFIN
TRIM
+
- 4.7 mF,
Low ESR
IN+
ADS8318
IN-
Figure 61. Direct External Reference Driving Circuit
POWER SAVING
The ADS8318 has an auto power-down feature. The device powers down at the end of every conversion. The
input signal is acquired on sampling capacitors while the device is in the power-down state, and at the same time
the conversion results are available for reading. The device powers up by itself on the start of the conversion. As
discussed before, the conversion runs on an internal clock and takes a fixed time. As a result, device power
consumption is directly proportional to the speed of operation.
DIGITAL OUTPUT
As discussed before (in the DESCRIPTION and TIMING DIAGRAMS sections) the device digital output is SPI
compatible. The following table lists the output codes corresponding to various analog input voltages.
DESCRIPTION
ANALOG VALUE (V)
DIGITAL OUTPUT STRAIGHT BINARY
Full-scale range
2*Vref
Least significant bit (LSB)
2*Vref/65536
Positive full scale
+Vref – 1 LSB
0111 1111 1111 1111
7FFF
Midscale
0V
0000 0000 0000 0000
0000
Midscale – 1 LSB
0 – 1 LSB
1111 1111 1111 1111
FFFF
Negative full scale
–Vref
1000 0000 0000 0000
8000
BINARY CODE
HEX CODE
SCLK INPUT
The device uses SCLK for serial data output. Data is read after the conversion is over and the device is in the
acquisition phase. It is possible to use a free running SCLK for the device, but it is recommended to stop the
clock during a conversion, as the clock edges can couple with the internal analog circuit and can affect
conversion results.
22
Submit Documentation Feedback
Copyright © 2008–2011, Texas Instruments Incorporated
Product Folder Link(s): ADS8318
ADS8318
SLAS568A – MAY 2008 – REVISED MARCH 2011
www.ti.com
REVISION HISTORY
Changes from Original (May 2008) to Revision A
Page
•
Changed Condition in first TIMING REQUIREMENTS from 4.5 V to 3.1 V ......................................................................... 5
•
Changed SCLK Low time MIN value from 9ns to 8ns and SCLK High time MIN value from 9ns to 8ns ............................. 5
•
Changed Condition in second TIMING REQUIREMENTS from +4.5 V to + 3.1 V .............................................................. 6
Submit Documentation Feedback
Copyright © 2008–2011, Texas Instruments Incorporated
Product Folder Link(s): ADS8318
23
PACKAGE OPTION ADDENDUM
www.ti.com
14-Oct-2022
PACKAGING INFORMATION
Orderable Device
Status
(1)
Package Type Package Pins Package
Drawing
Qty
Eco Plan
(2)
Lead finish/
Ball material
MSL Peak Temp
Op Temp (°C)
Device Marking
(3)
Samples
(4/5)
(6)
ADS8318IBDGSR
ACTIVE
VSSOP
DGS
10
2500
RoHS & Green
Call TI
Level-2-260C-1 YEAR
-40 to 85
CBC
Samples
ADS8318IBDGST
ACTIVE
VSSOP
DGS
10
250
RoHS & Green
Call TI
Level-2-260C-1 YEAR
-40 to 85
CBC
Samples
ADS8318IBDRCT
ACTIVE
VSON
DRC
10
250
RoHS & Green
Call TI
Level-3-260C-168 HR
-40 to 85
CBE
Samples
ADS8318IDGSR
ACTIVE
VSSOP
DGS
10
2500
RoHS & Green
Call TI
Level-2-260C-1 YEAR
-40 to 85
CBC
Samples
ADS8318IDGST
ACTIVE
VSSOP
DGS
10
250
RoHS & Green
Call TI
Level-2-260C-1 YEAR
-40 to 85
CBC
Samples
ADS8318IDRCT
ACTIVE
VSON
DRC
10
250
RoHS & Green
Call TI
Level-3-260C-168 HR
-40 to 85
CBE
Samples
(1)
The marketing status values are defined as follows:
ACTIVE: Product device recommended for new designs.
LIFEBUY: TI has announced that the device will be discontinued, and a lifetime-buy period is in effect.
NRND: Not recommended for new designs. Device is in production to support existing customers, but TI does not recommend using this part in a new design.
PREVIEW: Device has been announced but is not in production. Samples may or may not be available.
OBSOLETE: TI has discontinued the production of the device.
(2)
RoHS: TI defines "RoHS" to mean semiconductor products that are compliant with the current EU RoHS requirements for all 10 RoHS substances, including the requirement that RoHS substance
do not exceed 0.1% by weight in homogeneous materials. Where designed to be soldered at high temperatures, "RoHS" products are suitable for use in specified lead-free processes. TI may
reference these types of products as "Pb-Free".
RoHS Exempt: TI defines "RoHS Exempt" to mean products that contain lead but are compliant with EU RoHS pursuant to a specific EU RoHS exemption.
Green: TI defines "Green" to mean the content of Chlorine (Cl) and Bromine (Br) based flame retardants meet JS709B low halogen requirements of
工商网监
湘ICP备2023018690号
