TI1 ADS8320 16-bit, high-speed, 2.7v to 5v micropower sampling analog-to-digital converter Datasheet

ADS8320
SBAS108D – MAY 2000 – REVISED MARCH 2007
16-Bit, High-Speed, 2.7V to 5V microPower Sampling
ANALOG-TO-DIGITAL CONVERTER
FEATURES
DESCRIPTION
● 100kHz SAMPLING RATE
● microPOWER:
1.8mW at 100kHz and 2.7V
0.3mW at 10kHz and 2.7V
● POWER-DOWN: 3µA max
● MSOP-8 PACKAGE
● PIN-COMPATIBLE TO ADS7816 AND ADS7822
● SERIAL (SPI™/SSI) INTERFACE
The ADS8320 is a 16-bit, sampling analog-to-digital (A/D)
converter with ensured specifications over a 2.7V to 5.25V
supply range. It requires very little power even when operating at the full 100kHz data rate. At lower data rates, the high
speed of the device enables it to spend most of its time in the
power-down mode—the average power dissipation is less
than 100mW at 10kHz data rate.
APPLICATIONS
The ADS8320 also features operation from 2.0V to 5.25V, a
synchronous serial (SPI/SSI compatible) interface, and a
differential input. The reference voltage can be set to any
level within the range of 500mV to VCC.
Ultra-low power and small size make the ADS8320 ideal
for portable and battery-operated systems. It is also a
perfect fit for remote data acquisition modules, simultaneous multi-channel systems, and isolated data acquisition. The ADS8320 is available in an MSOP-8 package.
●
●
●
●
BATTERY-OPERATED SYSTEMS
REMOTE DATA ACQUISITION
ISOLATED DATA ACQUISITION
SIMULTANEOUS SAMPLING,
MULTICHANNEL SYSTEMS
● INDUSTRIAL CONTROLS
● ROBOTICS
● VIBRATION ANALYSIS
Control
SAR
VREF
DOUT
+In
CDAC
Serial
Interface
–In
S/H Amp
DCLOCK
CS/SHDN
Comparator
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.
SPI is a trademark of Motorola, Inc. All other trademarks are the property of their respective owners.
Copyright © 2000-2007, Texas Instruments Incorporated
PRODUCTION DATA information is current as of publication date.
Products conform to specifications per the terms of Texas Instruments
standard warranty. Production processing does not necessarily include
testing of all parameters.
www.ti.com
SPECIFICATIONS: +VCC = +5V
At –40°C to +85°C, VREF = +5V, –IN = GND, fSAMPLE = 100kHz, and fCLK = 24 • fSAMPLE, unless otherwise specified.
ADS8320E
PARAMETER
CONDITIONS
MIN
TYP
ADS8320EB
MAX
RESOLUTION
ANALOG INPUT
Full-Scale Input Span
Absolute Input Range
+In – (–In)
+In
–In
0
–0.1
–0.1
VREF
VCC + 0.1
+1.0
Capacitance
Leakage Current
SYSTEM PERFORMANCE
No Missing Codes
Integral Linearity Error
Offset Error
Offset Temperature Drift
Gain Error
Gain Temperature Drift
Noise
Power-Supply Rejection Ratio
REFERENCE INPUT
Voltage Range
Resistance
±0.006
±0.5
✻
±0.05
+4.7V < VCC < 5.25V
V
V
V
pF
nA
±0.012
±1
✻
✻
100
2.4
0.024
VIN = 5VPP at 10kHz
VIN = 5VPP at 10kHz
VIN = 5VPP at 10kHz
–86
84
86
92
0.5
VCC
5
5
40
0.8
0.1
✻
80
3
✻
✻
✻
CS = VCC
–40
✻
✻
✻
✻
0.4
V
GΩ
GΩ
µA
µA
µA
V
V
V
V
✻
Straight Binary
900
200
4.5
0.3
Clk Cycles
Clk Cycles
kHz
MHz
✻
VCC + 0.3
0.8
4.75
2.0
Bits
% of FSR
mV
µV/°C
%
ppm/°C
µVrms
LSB(1)
dB
dB
dB
dB
✻
✻
✻
✻
✻
✻
CMOS
3.0
–0.3
4.0
✻
✻
✻
–84
82
84
90
CS = GND, fSAMPLE = 0Hz
CS = VCC
TEMPERATURE RANGE
Specified Performance
✻
✻
✻
±0.024
16
Specified Performance
Bits
✻
✻
✻
4.5
fSAMPLE = 10kHz(3, 4)
Power Dissipation
Power-Down
±0.018
±2
±0.3
20
3
fSAMPLE = 10kHz
CS = VCC
POWER-SUPPLY REQUIREMENTS
VCC
VCC Range(2)
Quiescent Current
UNITS
✻
15
±0.008
±1
±3
IIH = +5µA
IIL = +5µA
IOH = –250µA
IOL = 250µA
MAX
✻
✻
14
Current Drain
DIGITAL INPUT/OUTPUT
Logic Family
Logic Levels:
VIH
VIL
VOH
VOL
Data Format
TYP
✻
✻
✻
45
1
SAMPLING DYNAMICS
Conversion Time
Acquisition Time
Throughput Rate
Clock Frequency Range
DYNAMIC CHARACTERISTICS
Total Harmonic Distortion
SINAD
Spurious-Free Dynamic Range
SNR
MIN
16
5.25
5.25
1700
✻
✻
✻
✻
✻
✻
8.5
3
+85
✻
✻
✻
✻
✻
✻
V
V
µA
µA
mW
µA
✻
°C
✻ Specifications same as ADS8320E.
NOTES: (1)
(2)
(3)
(4)
2
LSB means Least Significant Bit. With VREF equal to +5.0V, one LSB is 0.076mV.
See Typical Performance Curves for more information.
fCLK = 2.4MHz, CS = VCC for 216 clock cycles out of every 240.
See the Power Dissipation section for more information regarding lower sample rates.
ADS8320
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SBAS108D
SPECIFICATIONS: +VCC = +2.7V
At –40°C to +85°C, VREF = 2.5V, –IN = GND, fSAMPLE = 100kHz, and fCLK = 24 • fSAMPLE, unless otherwise specified.
ADS8320E
PARAMETER
CONDITIONS
MIN
TYP
ADS8320EB
MAX
RESOLUTION
ANALOG INPUT
Full-Scale Input Span
Absolute Input Range
+In – (–In)
+In
–In
0
–0.1
–0.1
Capacitance
Leakage Current
SYSTEM PERFORMANCE
No Missing Codes
Integral Linearity Error
Offset Error
Offset Temperature Drift
Gain Error
Gain Temperature Drift
Noise
Power-Supply Rejection Ratio
REFERENCE INPUT
Voltage Range
Resistance
±0.018
±2
±0.006
±0.5
✻
±0.05
±0.3
20
3
+2.7V < VCC < +3.3V
✻
✻
✻
100
2.4
VCC
5
5
20
0.1
✻
50
3
2.0
–0.3
2.1
VCC + 0.3
0.8
✻
✻
✻
2.7
2.0
2.0
650
100
1.8
0.3
CS = VCC
TEMPERATURE RANGE
Specified Performance
–40
Clk Cycles
Clk Cycles
kHz
MHz
dB
dB
dB
dB
✻
✻
✻
✻
✻
0.4
fSAMPLE = 10kHz(4,5)
Bits
% of FSR
mV
µV/°C
±0.024 % of FSR
ppm/°C
µVrms
LSB(1)
±0.012
±1
V
GΩ
GΩ
µA
µA
✻
V
V
V
V
✻
Straight Binary
See Note 2
V
V
V
pF
nA
✻
✻
✻
✻
✻
CMOS
Specified Performance
✻
✻
✻
–88
86
88
90
0.5
IIH = +5µA
IIL = +5µA
IOH = –250µA
IOL = 250µA
Bits
✻
✻
✻
–86
84
86
88
CS = GND, fSAMPLE = 0Hz
CS = VCC
UNITS
✻
✻
0.024
VIN = 2.7Vp-p at 1kHz
VIN = 2.7Vp-p at 1kHz
VIN = 2.7Vp-p at 1kHz
MAX
✻
16
4.5
Quiescent Current
Power Dissipation
Power-Down
✻
✻
✻
15
±0.008
±1
±3
CS = VCC
POWER-SUPPLY REQUIREMENTS
VCC
VCC Range(3)
TYP
✻
✻
14
Current Drain
DIGITAL INPUT/OUTPUT
Logic Family
Logic Levels:
VIH
VIL
VOH
VOL
Data Format
VREF
VCC + 0.1
+0.5
45
1
SAMPLING DYNAMICS
Conversion Time
Acquisition Time
Throughput Rate
Clock Frequency Range
DYNAMIC CHARACTERISTICS
Total Harmonic Distortion
SINAD
Spurious-Free Dynamic Range
SNR
MIN
16
3.3
5.25
2.7
1300
✻
✻
✻
✻
✻
✻
✻
3.8
3
+85
✻
✻
✻
✻
✻
✻
✻
V
V
V
µA
µA
mW
µA
✻
°C
✻ Specifications same as ADS8320E.
NOTES: (1)
(2)
(3)
(4)
(5)
LSB means Least Significant Bit. With VREF equal to +2.5V, one LSB is 0.038mV.
The maximum clock rate of the ADS8320 is less than 2.4MHz in this power supply range.
See the Typical Performance Curves for more information.
fCLK = 2.4MHz, CS = VCC for 216 clock cycles out of every 240.
See the Power Dissipation section for more information regarding lower sample rates.
ADS8320
SBAS108D
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3
ELECTROSTATIC
DISCHARGE SENSITIVITY
PIN CONFIGURATION
Top View
MSOP
VREF
1
+In
2
8
+VCC
7
DCLOCK
Electrostatic discharge can cause damage ranging from
performance degradation to complete device failure. Texas
Instruments recommends that all integrated circuits be handled
and stored using appropriate ESD protection methods.
ADS8320
–In
3
6
DOUT
GND
4
5
CS/SHDN
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
published specifications.
ABSOLUTE MAXIMUM RATINGS(1)
PIN ASSIGNMENTS
PIN
NAME
1
VREF
DESCRIPTION
2
+In
Noninverting Input.
3
–In
Inverting Input. Connect to ground or to remote
ground sense point.
Reference Input.
4
GND
5
CS/SHDN
Chip Select when LOW, Shutdown Mode when
HIGH.
Ground.
6
DOUT
The serial output data word is comprised of 16
bits of data. In operation the data is valid on the
falling edge of DCLOCK. The
second clock pulse after the falling edge of CS
enables the serial output. After one null bit the
data is valid for the next 16 edges.
7
DCLOCK
Data Clock synchronizes the serial data transfer
and determines conversion speed.
8
+VCC
VCC ....................................................................................................... +6V
Analog Input .............................................................. –0.3V to (VCC + 0.3V)
Logic Input ............................................................................... –0.3V to 6V
Case Temperature ......................................................................... +100°C
Junction Temperature .................................................................... +150°C
Storage Temperature ..................................................................... +125°C
External Reference Voltage .............................................................. +5.5V
Input current to any pin except supply ............................................ ±10mA
NOTE: (1) Stresses above these ratings may permanently damage the device.
Power Supply.
PACKAGE/ORDERING INFORMATION(1)
PRODUCT
ADS8320E
ADS8320E
ADS8320EB
ADS8320EB
MAXIMUM
INTEGRAL
LINEARITY
ERROR
(%)
NO
MISSING
CODE
ERROR
(LSB)
0.018
"
PACKAGE
PACKAGE
DESIGNATOR
SPECIFICATION
TEMPERATURE
RANGE
PACKAGE
MARKING(2)
ORDERING
NUMBER(3)
14
MSOP-8
DGK
–40°C to +85°C
A20
"
"
"
"
"
0.012
15
MSOP-8
DGK
–40°C to +85°C
A20
"
"
"
"
"
"
ADS8320E/250
ADS8320E/2K5
ADS8320EB/250
ADS8320EB/2K5
TRANSPORT
MEDIA
Tape
Tape
Tape
Tape
and
and
and
and
Reel
Reel
Reel
Reel
NOTES: (1) For the most current product and ordering information, see the Package Option Addendum at the end of this data sheet, or see the TI website
at www.ti.com.
(2) Performance Grade information is marked on the reel.
(3) Models with a slash(/) are available only in tape and reel in quantities indicated (for example, /250 indicates 250 units per reel, /2K5 indicates
2500 devices per reel). Ordering 2500 pieces of ”ADS8320E/2K5“ will get a single 2500-piece tape and reel.
4
ADS8320
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SBAS108D
TYPICAL PERFORMANCE CURVES
At TA = +25°C, VCC = +5V, VREF = +5V, fSAMPLE = 100kHz, and fCLK = 24 • fSAMPLE, unless otherwise specified.
INTEGRAL LINEARITY ERROR vs CODE (+25°C)
DIFFERENTIAL LINEARITY ERROR vs CODE (+25°C)
20
3.0
Differential Linearity Error (LSB)
Integral Linearity Error (LSB)
1.0
0.0
–1.0
–2.0
–3.0
–4.0
–5.0
–6.0
0000H
4000H
8000H
Hex Code
C000H
2.0
1.0
0.0
–1.0
–2.0
–3.0
0000H
FFFFH
C000H
FFFFH
POWER-DOWN SUPPLY CURRENT
vs TEMPERATURE
1200
600
1000
500
Supply Current (nA)
5V
800
2.7V
600
400
200
400
5V
300
200
100
0
0
–50
–25
0
25
50
75
100
–50
–25
0
Temperature (°C)
25
50
75
100
Temperature (°C)
QUIESCENT CURRENT vs VCC
MAXIMUM SAMPLE RATE vs VCC
1200
1000
1000
Sample Rate (kHz)
Quiescent Current (µA)
8000H
Hex Code
SUPPLY CURRENT vs TEMPERATURE
Supply Current (µA)
4000H
800
600
100
10
400
200
1
1
2
3
4
5
1
VCC (V)
ADS8320
SBAS108D
www.ti.com
2
3
VCC (V)
4
5
5
TYPICAL PERFORMANCE CURVES (Cont.)
At TA = +25°C, VCC = +2.7V, VREF = +2.5V, fSAMPLE = 100kHz, and fCLK = 24 • fSAMPLE, unless otherwise specified.
CHANGE IN OFFSET vs TEMPERATURE
CHANGE IN OFFSET vs REFERENCE VOLTAGE
3
6
VCC = 5V
2
4
Delta from +25 C (LSB)
Change in Offset (LSB)
5
3
2
1
0
–1
1
5V
0
2.7V
−1
−2
–2
−3
–3
1
2
3
Reference Voltage (V)
4
−50
5
−25
0
25
50
75
100
Temperature (°C)
CHANGE IN GAIN vs REFERENCE VOLTAGE
CHANGE IN GAIN vs TEMPERATURE
5
6
VCC = 5V
4
Delta from 25°C (LSB)
Change in Gain (LSB)
4
3
2
1
0
–2
5V
–2
2.7V
–6
1
2
3
Reference Voltage (V)
4
5
–50
–25
0
25
50
75
100
Temperature (°C)
FREQUENCY SPECTRUM
(8192 Point FFT, FIN = 10.120kHz, –0.3dB)
0
PEAK-TO-PEAK NOISE vs REFERENCE VOLTAGE
10
VCC = 5V
9
Peak-to-Peak Noise (LSB)
–20
–40
Amplitude (dB)
0
–4
–1
–60
–80
–100
–120
8
7
6
5
4
3
2
1
–140
0
0
6
2
10
20
30
Frequency (kHz)
40
0.1
50
1
Reference Voltage (V)
10
ADS8320
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SBAS108D
TYPICAL PERFORMANCE CURVES (Cont.)
At TA = +25°C, VCC = +5V, VREF = +5V, fSAMPLE = 100kHz, and fCLK = 24 • fSAMPLE, unless otherwise specified.
SPURIOUS-FREE DYNAMIC RANGE AND
SIGNAL-TO-NOISE RATIO vs FREQUENCY
TOTAL HARMONIC DISTORTION vs FREQUENCY
0
Signal-to-Noise Ratio
90
80
Spurious-Free Dynamic Range
70
–10
Total Harmonic Distortion (dB)
Spurious-Free Dynamic Range
and Signal-to-Noise Ratio (dB)
100
60
50
40
30
20
–20
–30
–40
–50
–60
–70
–80
10
–90
0
–100
1
10
Frequency (kHz)
50
100
1
SIGNAL-TO-(NOISE + DISTORTION) vs FREQUENCY
90
Signal-to-(Noise + Distortion) (dB)
Signal-to-(Noise + Distortion) (dB)
100
SIGNAL-TO-(NOISE + DISTORTION) vs INPUT LEVEL
100
90
80
70
60
50
40
30
20
10
1
10
Frequency (kHz)
50
80
70
60
50
40
30
20
–40
0
100
REFERENCE CURRENT vs SAMPLE RATE
70
60
60
50
40
5V
30
20
–35
–30
–25
–20
–15
Input Level (dB)
–10
–5
0
REFERENCE CURRENT vs TEMPERATURE
70
Reference Current (µA)
Reference Current (µA)
10
Frequency (kHz)
2.7V
50
5V
40
30
2.7V
20
10
0
0
20
40
60
Sample Rate (kHz)
80
10
–50
100
0
25
50
75
100
Temperature (°C)
ADS8320
SBAS108D
–25
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7
THEORY OF OPERATION
The ADS8320 is a classic successive approximation register
(SAR) analog-to-digital (A/D) converter. The architecture is
based on capacitive redistribution, which inherently includes
a sample/hold function. The converter is fabricated on a 0.6µ
CMOS process. The architecture and process allow the
ADS8320 to acquire and convert an analog signal at up to
100,000 conversions per second while consuming less than
4.5mW from +VCC.
The ADS8320 requires an external reference, an external
clock, and a single power source (VCC). The external reference can be any voltage between 500mV and VCC. The value
of the reference voltage directly sets the range of the analog
input. The reference input current depends on the conversion
rate of the ADS8320.
The external clock can vary between 24kHz (1kHz throughput) and 2.4MHz (100kHz throughput). The duty cycle of
the clock is essentially unimportant, as long as the minimum
high and low times are at least 200ns (VCC = 2.7V or
greater). The minimum clock frequency is set by the leakage
on the capacitors internal to the ADS8320.
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 inputs are disconnected from
any internal function.
The digital result of the conversion is clocked out by the
DCLOCK input and is provided serially, most significant bit
first, on the DOUT pin. The digital data that is provided on the
DOUT pin is for the conversion currently in progress—there
is no pipeline delay. It is possible to continue to clock the
ADS8320 after the conversion is complete and to obtain the
serial data least significant bit first. See the digital timing
section for more information.
ANALOG INPUT
The +In and –In input pins allow for a differential input
signal. Unlike some converters of this type, the –In input is
not re-sampled later in the conversion cycle. When the
converter goes into the hold mode, the voltage difference
between +In and –In is captured on the internal capacitor
array.
The range of the –In input is limited to –0.1V to +1V (–0.1V
to +0.5V when using a 2.7V supply). Because of this, the
differential input can be used to reject only small signals that
are common to both inputs. Thus, the –In input is best used
to sense a remote signal ground that may move slightly with
respect to the local ground potential.
The input current on the analog inputs depends on a number
of factors: sample rate, input voltage, source impedance, and
power-down mode. Essentially, the current into the ADS8320
8
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 (45pF)
to a 16-bit settling level within 4.5 clock cycles. When the
converter goes into the hold mode or while it is in the powerdown mode, the input impedance is greater than 1GΩ.
Care must be taken regarding the absolute analog input
voltage. To maintain the linearity of the converter, the –In
input should not drop below GND – 100mV or exceed
GND + 1V. The +In input should always remain within the
range of GND – 100mV to VCC + 100mV. Outside of these
ranges, the converter linearity may not meet specifications.
To minimize noise, low bandwidth input signals with lowpass filters should be used.
REFERENCE INPUT
The external reference sets the analog input range. The
ADS8320 operates with a reference in the range of 500mV
to VCC. There are several important implications of this.
As the reference voltage is reduced, the analog voltage
weight of each digital output code is reduced. This is often
referred to as the Least Significant Bit (LSB) size and is
equal to the reference voltage divided by 65,536. This means
that any offset or gain error inherent in the A/D converter
will appear to increase, in terms of LSB size, as the reference
voltage is reduced.
The noise inherent in the converter also appears to increase
with lower LSB size. With a +5V reference, the internal
noise of the converter typically contributes only 1.5 LSB
peak-to-peak of potential error to the output code. When the
external reference is 500mV, the potential error contribution
from the internal noise will be 10 times larger—15 LSBs.
The errors due to the internal noise are gaussian in nature
and can be reduced by averaging consecutive conversion
results.
For more information regarding noise, consult the typical
performance curve “Peak-to-Peak Noise vs Reference Voltage.” Note that the Effective Number of Bits (ENOB) figure
is calculated based on the converter’s signal-to-(noise +
distortion) ratio with a 1kHz, 0dB input signal. SINAD is
related to ENOB as follows:
SINAD = 6.02 • ENOB + 1.76
With lower reference voltages, extra care should be taken to
provide a clean layout including adequate bypassing, a clean
power supply, a low-noise reference, and a low-noise input
signal. Because the LSB size is lower, the converter is also
more sensitive to external sources of error such as nearby
digital signals and electromagnetic interference.
ADS8320
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SBAS108D
NOISE
The noise floor of the ADS8320 itself is extremely low, as
can be seen from Figures 1 and 2, and is much lower than
competing A/D converters. It was tested by applying a lownoise DC input and a 5.0V reference to the ADS8320 and
initiating 5000 conversions. The digital output of the A/D
2510
0
0
1
2
2490
3
4
0
0
5
6
Code
FIGURE 1. Histogram of 5000 Conversions of a DC Input
at the Code Transition.
4864
converter varies in output code due to the internal noise of
the ADS8320. This is true for all 16-bit SAR-type A/D
converters. Using a histogram to plot the output codes, the
distribution should appear bell-shaped with the peak of the
bell curve representing the nominal code for the input value.
The ±1σ, ±2σ, and ±3σ distributions represents the 68.3%,
95.5%, and 99.7%, respectively, of all codes. The transition
noise can be calculated by dividing the number of codes
measured by 6 and this yields the ±3σ distribution or 99.7%
of all codes. Statistically, up to 3 codes could fall outside the
distribution when executing 1000 conversions. The
ADS8320, with < 3 output codes for the ±3σ distribution,
yields a < ±0.5LSB transition noise. Remember, to achieve
this low noise performance, the peak-to-peak noise of the
input signal and reference must be < 50µV.
AVERAGING
The noise of the A/D converter can be compensated by
averaging the digital codes. By averaging conversion results, transition noise is reduced by a factor of 1/√n, where
n is the number of averages. For example, averaging four
conversion results reduces the transition noise by 1/2 to
±0.25 LSBs. Averaging should only be used for input
signals with frequencies near DC.
For AC signals, a digital filter can be used to low-pass filter
and decimate the output codes. This works in a similar
manner to averaging; for every decimation by 2, the signalto-noise ratio improves 3dB.
DIGITAL INTERFACE
0
0
72
1
2
3
4
64
0
5
6
SIGNAL LEVELS
The digital inputs of the ADS8320 can accommodate logic
levels up to 5.5V regardless of the value of VCC. Thus, the
ADS8320 can be powered at 3V and still accept inputs from
logic powered at 5V.
The CMOS digital output (DOUT) swings 0V to VCC. If VCC
is 3V and this output is connected to a 5V CMOS logic
input, then that IC may require more supply current than
normal and may have a slightly longer propagation delay.
Code
FIGURE 2. Histogram of 5000 Conversions of a DC Input
at the Code Center.
ADS8320
SBAS108D
www.ti.com
9
SERIAL INTERFACE
The ADS8320 communicates with microprocessors and other
digital systems via a synchronous 3-wire serial interface, as
shown in Figure 3 and Table I. The DCLOCK signal synchronizes the data transfer with each bit being transmitted on
the falling edge of DCLOCK. Most receiving systems will
capture the bitstream on the rising edge of DCLOCK. However, if the minimum hold time for DOUT is acceptable, the
system can use the falling edge of DCLOCK to capture each
bit.
A falling CS signal initiates the conversion and data transfer.
The first 4.5 to 5.0 clock periods of the conversion cycle are
used to sample the input signal. After the fifth falling
DCLOCK edge, DOUT is enabled and outputs a LOW value
for one clock period. For the next 16 DCLOCK periods,
DOUT outputs the conversion result, most significant bit first.
After the least significant bit (B0) has been output, subsequent clocks repeat the output data but in a least significant
bit first format.
After the most significant bit (B15) has been repeated, DOUT
will tri-state. Subsequent clocks will have no effect on the
converter. A new conversion is initiated only when CS has
been taken HIGH and returned LOW.
SYMBOL
DESCRIPTION
MIN
tSMPL
Analog Input Sample Time
4.5
TYP
MAX
UNITS
5.0
Clk Cycles
tCONV
Conversion Time
tCYC
Throughput Rate
100
kHz
tCSD
CS Falling to
DCLOCK LOW
0
ns
tSUCS
CS Falling to
DCLOCK Rising
20
thDO
DCLOCK Falling to
Current DOUT Not Valid
5
tdDO
DCLOCK Falling to Next
DOUT Valid
tdis
ten
16
Clk Cycles
ns
15
ns
30
50
ns
CS Rising to DOUT Tri-State
70
100
ns
DCLOCK Falling to DOUT
Enabled
20
50
ns
tf
DOUT Fall Time
5
25
ns
tr
DOUT Rise Time
7
25
ns
DATA FORMAT
The output data from the ADS8320 is in Straight Binary
format, as shown in Table II. This table represents the ideal
output code for the given input voltage and does not include
the effects of offset, gain error, or noise.
DESCRIPTION
ANALOG VALUE
Full-Scale Range
VREF
Least Significant
Bit (LSB)
VREF/65,536
DIGITAL OUTPUT
STRAIGHT BINARY
BINARY CODE
HEX CODE
Full-Scale
VREF – 1 LSB
1111 1111 1111 1111
FFFF
Midscale
VREF/2
1000 0000 0000 0000
8000
VREF/2 – 1 LSB
0111 1111 1111 1111
7FFF
0V
0000 0000 0000 0000
0000
Midscale – 1LSB
Zero
TABLE II. Ideal Input Voltages and Output Codes.
POWER DISSIPATION
The architecture of the converter, the semiconductor fabrication process, and a careful design allow the ADS8320 to
convert at up to a 100kHz rate while requiring very little
power. Still, for the absolute lowest power dissipation, there
are several things to keep in mind.
The power dissipation of the ADS8320 scales directly with
conversion rate. Therefore, the first step to achieving the
lowest power dissipation is to find the lowest conversion
rate that satisfies the requirements of the system.
In addition, the ADS8320 is in power-down mode under two
conditions: when the conversion is complete and whenever
CS is HIGH (as shown in Figure 3). Ideally, each conversion
should occur as quickly as possible, preferably at a 2.4MHz
clock rate. This way, the converter spends the longest
possible time in the power-down mode. This is very important as the converter not only uses power on each DCLOCK
transition (as is typical for digital CMOS components), but
also uses some current for the analog circuitry, such as the
comparator. The analog section dissipates power continuously, until the power-down mode is entered.
TABLE I. Timing Specifications (VCC = 2.7V and above,
–40°C to +85°C.
Complete Cycle
CS/SHDN
tSUCS
Sample
Power Down
Conversion
DCLOCK
tCSD
DOUT
Use positive clock edge for data transfer
Hi-Z
0
tSMPL
B15 B14 B13 B12 B11 B10 B9 B8
(MSB)
tCONV
B7
B6
B5 B4
B3
B2
B1
B0
(LSB)
Hi-Z
NOTE: Minimum 22 clock cycles required for 16-bit conversion. Shown are 24 clock cycles.
If CS remains LOW at the end of conversion, a new datastream with LSB-first is shifted out again.
FIGURE 3. ADS8320 Basic Timing Diagrams.
10
ADS8320
www.ti.com
SBAS108D
1.4V
3kΩ
DOUT
VOH
DOUT
VOL
Test Point
tr
100pF
CLOAD
tf
Voltage Waveforms for DOUT Rise and Fall Times, tr, tf
Load Circuit for tdDO, tr, and tf
Test Point
DCLOCK
VIL
VCC
DOUT
tdDO
VOH
DOUT
tdis Waveform 2, ten
3kΩ
tdis Waveform 1
100pF
CLOAD
VOL
thDO
Load Circuit for tdis and ten
Voltage Waveforms for DOUT Delay Times, tdDO
VIH
CS/SHDN
DOUT
Waveform 1(1)
CS/SHDN
90%
DCLOCK
1
4
5
tdis
DOUT
Waveform 2(2)
VOL
DOUT
10%
B11
ten
Voltage Waveforms for tdis
Voltage Waveforms for ten
NOTES: (1) Waveform 1 is for an output with internal conditions such that the output
is HIGH unless disabled by the output control. (2) Waveform 2 is for an output with
internal conditions such that the output is LOW unless disabled by the output control.
FIGURE 4. Timing Diagrams and Test Circuits for the Parameters in Table I.
ADS8320
SBAS108D
www.ti.com
11
LAYOUT
For optimum performance, care should be taken with the
physical layout of the ADS8320 circuitry. This is particularly true if the reference voltage is low and/or the conversion rate is high. At a 100kHz conversion rate, the ADS8320
makes a bit decision every 416ns. That is, for each subsequent bit decision, the digital output must be updated with
the results of the last bit decision, the capacitor array
appropriately switched and charged, and the input to the
comparator settled to a 16-bit level all within one clock
cycle.
12
Supply Current (µA)
TA = 25°C
fCLK = 2.4MHz
100
VCC = 2.7V
VREF = 2.5V
VCC = 5.0V
VREF = 5.0V
10
1
0.1
1
10
100
Sample Rate (kHz)
FIGURE 5. Maintaining fCLK at the Highest Possible Rate
Allows Supply Current to Drop Linearly with
Sample Rate.
1000
Supply Current (µA)
SHORT CYCLING
Another way of saving power is to utilize the CS signal to
short cycle the conversion. Because the ADS8320 places the
latest data bit on the DOUT line as it is generated, the
converter can easily be short cycled. This term means that
the conversion can be terminated at any time. For example,
if only 14 bits of the conversion result are needed, then the
conversion can be terminated (by pulling CS HIGH) after
the 14th bit has been clocked out.
This technique can be used to lower the power dissipation
(or to increase the conversion rate) in those applications
where an analog signal is being monitored until some condition becomes true. For example, if the signal is outside a
predetermined range, the full 16-bit conversion result may
not be needed. If so, the conversion can be terminated after
the first n bits, where n might be as low as 3 or 4. This results
in lower power dissipation in both the converter and the rest
of the system, as they spend more time in the power-down
mode.
1000
100
10
TA = 25°C
VCC = 5.0V
VREF = 5.0V
fCLK = 24 • fSAMPLE
1
0.1
1
10
100
Sample Rate (kHz)
FIGURE 6. Scaling fCLK Reduces Supply Current Only
Slightly with Sample Rate.
1000
TA = 25°C
VCC = 5.0V
VREF = 5.0V
fCLK = 24 • fSAMPLE
800
Supply Current (µA)
Figure 5 shows the current consumption of the ADS8320
versus sample rate. For this graph, the converter is clocked
at 2.4MHz regardless of the sample rate—CS is HIGH for
the remaining sample period. Figure 6 also shows current
consumption versus sample rate. However, in this case, the
DCLOCK period is 1/24th of the sample period—CS is
HIGH for one DCLOCK cycle out of every 16.
There is an important distinction between the power-down
mode that is entered after a conversion is complete and the
full power-down mode which is enabled when CS is HIGH.
CS LOW will shut down only the analog section. The digital
section is completely shut down only when CS is HIGH.
Thus, if CS is left LOW at the end of a conversion and the
converter is continually clocked, the power consumption
will not be as low as when CS is HIGH. Figure 7 shows
more information.
Power dissipation can also be reduced by lowering the
power-supply voltage and the reference voltage. The
ADS8320 operates over a VCC range of 2.0V to 5.25V.
However, at voltages below 2.7V, the converter will not run
at a 100kHz sample rate. See the typical performance curves
for more information regarding power supply voltage and
maximum sample rate.
600
CS LOW (GND)
400
200
0.0
CS HIGH (VCC)
0.250
0.00
0.1
1
10
100
Sample Rate (kHz)
FIGURE 7. Shutdown Current with CS HIGH is 50nA
Typically, Regardless of the Clock. Shutdown
Current with CS LOW Varies with Sample
Rate.
ADS8320
www.ti.com
SBAS108D
The basic SAR architecture is sensitive to spikes on the
power supply, reference, and ground connections that occur
just prior to latching the comparator output. Thus, during
any single conversion for an n-bit SAR converter, there are
n “windows” in which large external transient voltages can
easily affect the conversion result. Such spikes might originate from switching power supplies, digital logic, and high
power devices, to name a few. This particular source of error
can be very difficult to track down if the glitch is almost
synchronous to the converter DCLOCK signal—as the phase
difference between the two changes with time and temperature, causing sporadic misoperation.
With this in mind, power to the ADS8320 should be clean
and well bypassed. A 0.1µF ceramic bypass capacitor should
be placed as close to the ADS8320 package as possible. In
addition, a 1µF to 10µF capacitor and a 5Ω or 10Ω series
resistor may be used to low-pass filter a noisy supply.
The reference should be similarly bypassed with a 0.1µF
capacitor. Again, a series resistor and large capacitor can be
used to low-pass filter the reference voltage. If the reference
voltage originates from an op amp, be careful that the op
amp can drive the bypass capacitor without oscillation (the
series resistor can help in this case). Keep in mind that while
the ADS8320 draws very little current from the reference on
average, there are still instantaneous current demands placed
on the external input and reference circuitry.
Texas Instruments' OPA627 op amp provides optimum
performance for buffering both the signal and reference
inputs. For low-cost, low-voltage, single-supply applications, the OPA2350 or OPA2340 dual op amps are recommended.
Also, keep in mind that the ADS8320 offers no inherent
rejection of noise or voltage variation in regards to the
reference input. This is of particular concern when the
reference input is tied to the power supply. Any noise and
ripple from the supply will appear directly in the digital
results. While high-frequency noise can be filtered out as
described in the previous paragraph, voltage variation due to
the line frequency (50Hz or 60Hz), can be difficult to
remove.
The GND pin on the ADS8320 should be placed on a clean
ground point. In many cases, this will be the “analog”
ground. Avoid connecting the GND pin too close to the
grounding point for a microprocessor, microcontroller, or
digital signal processor. If needed, run a ground trace directly from the converter to the power-supply connection
point. The ideal layout includes an analog ground plane for
the converter and associated analog circuitry.
APPLICATION CIRCUITS
Figure 8 shows a basic data acquisition system. The ADS8320
input range is 0V to VCC, as the reference input is connected
directly to the power supply. The 5Ω resistor and 1µF to
10µF capacitor filter the microcontroller “noise” on the
supply, as well as any high-frequency noise from the supply
itself. The exact values should be picked such that the filter
provides adequate rejection of the noise.
+2.7V to +5.25V
5Ω
+ 1µF to
10µF
ADS8320
VREF
VCC
0.1µF
+In
CS
–In
DOUT
GND
+ 1µF to
10µF
Microcontroller
DCLOCK
FIGURE 8. Basic Data Acquisition System.
ADS8320
SBAS108D
www.ti.com
13
Revision History
DATE
REVISION
PAGE
SECTION
3/07
D
4
Absolute Max Ratings
7/06
C
6
Typ Performance Curves
DESCRIPTION
Added last row, Input current to any pin except supply...±10mA
Changed CHANGE IN OFFSET vs TEMPERATURE plot
NOTE: Page numbers for previous revisions may differ from page numbers in the current version.
14
ADS8320
www.ti.com
SBAS108D
PACKAGE OPTION ADDENDUM
www.ti.com
11-Apr-2013
PACKAGING INFORMATION
Orderable Device
Status
(1)
Package Type Package Pins Package
Drawing
Qty
Eco Plan
Lead/Ball Finish
(2)
MSL Peak Temp
Op Temp (°C)
Top-Side Markings
(3)
(4)
ADS8320E/250
ACTIVE
VSSOP
DGK
8
250
Green (RoHS CU NIPDAUAG Level-2-260C-1 YEAR
& no Sb/Br)
-40 to 85
A20
ADS8320E/250G4
ACTIVE
VSSOP
DGK
8
250
Green (RoHS CU NIPDAUAG Level-2-260C-1 YEAR
& no Sb/Br)
-40 to 85
A20
ADS8320E/2K5
ACTIVE
VSSOP
DGK
8
2500
Green (RoHS CU NIPDAUAG Level-2-260C-1 YEAR
& no Sb/Br)
-40 to 85
A20
ADS8320E/2K5G4
ACTIVE
VSSOP
DGK
8
2500
Green (RoHS CU NIPDAUAG Level-2-260C-1 YEAR
& no Sb/Br)
-40 to 85
A20
ADS8320EB/250
ACTIVE
VSSOP
DGK
8
250
Green (RoHS CU NIPDAUAG Level-2-260C-1 YEAR
& no Sb/Br)
-40 to 85
A20
ADS8320EB/250G4
ACTIVE
VSSOP
DGK
8
250
Green (RoHS CU NIPDAUAG Level-2-260C-1 YEAR
& no Sb/Br)
-40 to 85
A20
ADS8320EB/2K5
ACTIVE
VSSOP
DGK
8
2500
Green (RoHS CU NIPDAUAG Level-2-260C-1 YEAR
& no Sb/Br)
-40 to 85
A20
ADS8320EB/2K5G4
ACTIVE
VSSOP
DGK
8
2500
Green (RoHS CU NIPDAUAG Level-2-260C-1 YEAR
& no Sb/Br)
-40 to 85
A20
(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)
Eco Plan - The planned eco-friendly classification: Pb-Free (RoHS), Pb-Free (RoHS Exempt), or Green (RoHS & no Sb/Br) - please check http://www.ti.com/productcontent for the latest availability
information and additional product content details.
TBD: The Pb-Free/Green conversion plan has not been defined.
Pb-Free (RoHS): TI's terms "Lead-Free" or "Pb-Free" mean semiconductor products that are compatible with the current RoHS requirements for all 6 substances, including the requirement that
lead not exceed 0.1% by weight in homogeneous materials. Where designed to be soldered at high temperatures, TI Pb-Free products are suitable for use in specified lead-free processes.
Pb-Free (RoHS Exempt): This component has a RoHS exemption for either 1) lead-based flip-chip solder bumps used between the die and package, or 2) lead-based die adhesive used between
the die and leadframe. The component is otherwise considered Pb-Free (RoHS compatible) as defined above.
Green (RoHS & no Sb/Br): TI defines "Green" to mean Pb-Free (RoHS compatible), and free of Bromine (Br) and Antimony (Sb) based flame retardants (Br or Sb do not exceed 0.1% by weight
in homogeneous material)
(3)
MSL, Peak Temp. -- The Moisture Sensitivity Level rating according to the JEDEC industry standard classifications, and peak solder temperature.
Addendum-Page 1
Samples
PACKAGE OPTION ADDENDUM
www.ti.com
11-Apr-2013
(4)
Multiple Top-Side Markings will be inside parentheses. Only one Top-Side Marking contained in parentheses and separated by a "~" will appear on a device. If a line is indented then it is a
continuation of the previous line and the two combined represent the entire Top-Side Marking for that device.
Important Information and Disclaimer:The information provided on this page represents TI's knowledge and belief as of the date that it is provided. TI bases its knowledge and belief on information
provided by third parties, and makes no representation or warranty as to the accuracy of such information. Efforts are underway to better integrate information from third parties. TI has taken and
continues to take reasonable steps to provide representative and accurate information but may not have conducted destructive testing or chemical analysis on incoming materials and chemicals.
TI and TI suppliers consider certain information to be proprietary, and thus CAS numbers and other limited information may not be available for release.
In no event shall TI's liability arising out of such information exceed the total purchase price of the TI part(s) at issue in this document sold by TI to Customer on an annual basis.
OTHER QUALIFIED VERSIONS OF ADS8320 :
NOTE: Qualified Version Definitions:
Addendum-Page 2
PACKAGE MATERIALS INFORMATION
www.ti.com
13-Feb-2016
TAPE AND REEL INFORMATION
*All dimensions are nominal
Device
Package Package Pins
Type Drawing
SPQ
Reel
Reel
A0
Diameter Width (mm)
(mm) W1 (mm)
B0
(mm)
K0
(mm)
P1
(mm)
W
Pin1
(mm) Quadrant
ADS8320E/250
VSSOP
DGK
8
250
180.0
12.4
5.3
3.4
1.4
8.0
12.0
Q1
ADS8320E/2K5
VSSOP
DGK
8
2500
330.0
12.4
5.3
3.4
1.4
8.0
12.0
Q1
ADS8320EB/250
VSSOP
DGK
8
250
180.0
12.4
5.3
3.4
1.4
8.0
12.0
Q1
ADS8320EB/2K5
VSSOP
DGK
8
2500
330.0
12.4
5.3
3.4
1.4
8.0
12.0
Q1
Pack Materials-Page 1
PACKAGE MATERIALS INFORMATION
www.ti.com
13-Feb-2016
*All dimensions are nominal
Device
Package Type
Package Drawing
Pins
SPQ
Length (mm)
Width (mm)
Height (mm)
ADS8320E/250
VSSOP
DGK
8
250
210.0
185.0
35.0
ADS8320E/2K5
VSSOP
DGK
8
2500
367.0
367.0
38.0
ADS8320EB/250
VSSOP
DGK
8
250
210.0
185.0
35.0
ADS8320EB/2K5
VSSOP
DGK
8
2500
367.0
367.0
38.0
Pack Materials-Page 2
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