ADS8323
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SBAS224C – DECEMBER 2001 – REVISED JANUARY 2010
16-Bit, 500kSPS, microPower Sampling
ANALOG-TO-DIGITAL CONVERTER
Check for Samples: ADS8323
FEATURES
1
•
•
•
•
•
2
DESCRIPTION
HIGH-SPEED PARALLEL INTERFACE
500kSPS SAMPLING RATE
LOW POWER: 85mW at 500kSPS
BIPOLAR INPUT RANGE
TQFP-32 PACKAGE
The ADS8323 is a 16-bit, 500kSPS analog-to-digital
converter (ADC) with an internal 2.5V reference. The
device includes a 16-bit, capacitor-based successive
approximation register (SAR) ADC with inherent
sample-and-hold. The ADS8323 offers a full 16-bit
interface, or an 8-bit option where data are read using
two read cycles. The ADS8323 is available in a
TQFP-32 package and is specified over the industrial
–40°C to +85°C temperature range.
APPLICATIONS
•
•
•
•
HIGH-SPEED DATA ACQUISITION
OPTICAL POWER MONITORING
MOTOR CONTROL
ATE
white space here
white space here
white space here
white space here
white space here
BYTE
SAR
ADS8323
Output Latches
and
3-State
Drivers
Parallel
Data
Output
+IN
CDAC
-IN
S/H Amp
CLOCK
Comparator
REFIN
REFOUT
Internal
+2.5V Ref
Conversion
and Control
Logic
CONVST
CS
RD
BUSY
1
2
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.
All trademarks are the property of their respective owners.
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 © 2001–2010, Texas Instruments Incorporated
ADS8323
SBAS224C – DECEMBER 2001 – REVISED JANUARY 2010
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)
PRODUCT
MAXIMUM
INTEGRAL
LINEARITY
ERROR (LSB)
NO
MISSING
CODES
ERROR (LSB)
ADS8323Y
±8
14
PACKAGE-LEAD
PACKAGE
DESIGNATOR
SPECIFIED
TEMPERATURE
RANGE
TQFP-32
PBS
–40°C to +85°C
PACKAGE
MARKING
TRANSPORT
MEDIA, QUANTITY
Tape and reel, 250
Tape and reel, 2000
Tape and reel, 250
ADS8323YB
±6
15
TQFP-32
PBS
–40°C to +85°C
Tape and reel, 2000
(1)
For the most current package and ordering information, see the Package Option Addendum at the end of this data sheet, or see the TI
website at www.ti.com.
ABSOLUTE MAXIMUM RATINGS (1)
Over operating free-air temperature range (unless otherwise noted).
ADS8323
UNIT
Supply voltage, DGND to DVDD
–0.3 to 6
V
Supply voltage, AGND to AVDD
–0.3 to 6
V
Analog input voltage range
AGND – 0.3 to AVDD + 0.3
V
Reference input voltage
AGND – 0.3 to AVDD + 0.3
V
Digital input voltage range
DGND – 0.3 to DVDD + 0.3
V
±0.3
V
Ground voltage differences, AGND to DGND
Voltage differences, DVDD to AGND
–0.3 to 6
V
850
mW
Operating virtual junction temperature range, TJ
–40 to +150
°C
Operating free-air temperature range, TA
–40 to +85
°C
Storage temperature range
–65 to +150
°C
Power dissipation
(1)
Stresses above 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 conditions for extended periods may affect device reliability.
RECOMMENDED OPERATING CONDITIONS
Over operating free-air temperature range (unless otherwise noted).
PARAMETER
MIN
NOM
MAX
UNIT
AVDD (1)
4.75
5.0
5.25
V
DVDD (1)
4.75
5.0
5.25
V
+REFIN
V
2.55
V
POWER SUPPLY
ANALOG/REFERENCE INPUTS
Differential analog input voltage, IN+ to IN–
–REFIN
External reference voltage
(1)
1.5
2.5
The voltage difference between AVDD and DVDD terminals cannot exceed 0.3V to maintain performance specifications.
DISSIPATION RATINGS
(1)
2
PACKAGE
TA ≤ +25°C POWER RATING
DERATING FACTOR
ABOVE TA = +25°C (1)
TA = +70°C POWER RATING
TA = +85°C POWER RATING
TQFP-32
1636mW
13.09mW/°C
1047mW
850mW
This is the inverse of the traditional junction-to-ambient thermal resistance (RθJA). Thermal resistances are not production tested and are
for informational purposes only.
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ADS8323
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SBAS224C – DECEMBER 2001 – REVISED JANUARY 2010
ELECTRICAL CHARACTERISTICS
At –40°C to +85°C, +DVDD = +AVDD = +5V, VREF = +2.5V, fSAMPLE = 500kSPS, and fCLK = 20 • fSAMPLE, unless otherwise
specified.
ADS8323YB (1)
ADS8323Y
PARAMETER
TEST CONDITIONS
MIN
TYP
MAX
MIN
TYP
MAX
UNIT
RESOLUTION
Resolution
16
16
Bits
ANALOG INPUT
Full-scale input span (2)
Absolute input range
+IN – (–IN)
–VREF
+VREF
–VREF
+VREF
V
+IN
–0.3
AVDD + 0.3
–0.3
AVDD + 0.3
V
–IN
–0.3
AVDD + 0.3
–0.3
AVDD + 0.3
V
Capacitance
25
25
pF
Leakage current
±1
±1
nA
SYSTEM PERFORMANCE
No missing codes
14
15
Integral linearity error
±4
Differential linearity error
±3
Offset error
Gain error (4)
Common-mode rejection ratio
±3
±1
±2
±0.5
±1.0
mV
±0.25
±0.50
±0.12
±0.25
%FSR
±1
LSB
At dc
70
70
VIN = 1VPP at 1MHz
50
50
dB
60
60
μVRMS
±3
±3
LSBs
Noise
Power-supply rejection ratio
Bits
±6
LSB (3)
±8
At FFFFh output code
dB
SAMPLING DYNAMICS
Conversion time
1.6
Acquisition time
350
1.6
μs
500
kSPS
350
Throughput rate
ns
500
Aperture delay
10
10
Aperture jitter
30
30
ns
ps
Small-signal bandwidth
20
20
MHz
Step response
100
100
ns
Overvoltage recovery
150
150
ns
DYNAMIC CHARACTERISTICS
Total harmonic distortion (5)
VIN = 5VPP at 100kHz
–90
–93
dB
SINAD
VIN = 5VPP at 100kHz
81
83
dB
Spurious free dynamic range
VIN = 5VPP at 100kHz
94
96
dB
REFERENCE OUTPUT
Voltage
Source current
Drift
Line regulation
IOUT = 0
2.475
2.50
Static load
2.525
2.48
2.50
10
2.52
V
10
μA
IOUT = 0
25
25
ppm/°C
4.75V ≤ VCC ≤ 5.25V
0.6
0.6
mV
REFERENCE INPUT
Range
(1)
(2)
(3)
(4)
(5)
1.5
2.55
1.5
2.55
V
Shaded cells indicate different specifications from ADS8322Y.
Ideal input span; does not include gain or offset error.
LSB means least significant bit, with VREF equal to +2.5V; 1LSB = 76μV.
Measured relative to an ideal, full-scale input [+In – (–In)] of 4.9999V. Thus, gain error includes the error of the internal voltage
reference.
Calculated on the first nine harmonics of the input frequency.
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ADS8323
SBAS224C – DECEMBER 2001 – REVISED JANUARY 2010
www.ti.com
ELECTRICAL CHARACTERISTICS (continued)
At –40°C to +85°C, +DVDD = +AVDD = +5V, VREF = +2.5V, fSAMPLE = 500kSPS, and fCLK = 20 • fSAMPLE, unless otherwise
specified.
ADS8323YB (1)
ADS8323Y
PARAMETER
TEST CONDITIONS
MIN
TYP
MAX
MIN
TYP
MAX
UNIT
DIGITAL INPUT/OUTPUT
Logic family
CMOS
CMOS
Logic levels:
VIH
IIH ≤ +5μA
3.0
+DVDD
3.0
+DVDD
V
VIL
IIL ≤ –5μA
–0.3
0.8
–0.3
0.8
V
VOH
IOH = –1.6mA
4.0
VOL
IOH = +1.6mA
Data format
4.0
V
0.4
0.4
Binary twos complement
Binary twos complement
V
POWER-SUPPLY REQUIREMENTS
Power-supply voltage
+AVDD
4.75
5
5.25
4.75
5
5.25
+DVDD
4.75
5
5.25
4.75
5
5.25
V
V
Supply current
fSAMPLE = 500kSPS
17
25
17
25
mA
Power dissipation
fSAMPLE = 500kSPS
85
125
85
125
mW
+85
°C
TEMPERATURE RANGE
Specified performance
–40
+85
–40
EQUIVALENT INPUT CIRCUITS
DVDD
AVDD
RON
20W
C(SAMPLE)
20pF
DIN
AIN
DGND
AGND
Diode Turn-On Voltage: 0.35V
Equivalent Analog Input Circuit
4
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Equivalent Digital Input Circuit
Copyright © 2001–2010, Texas Instruments Incorporated
Product Folder Link(s): ADS8323
ADS8323
www.ti.com
SBAS224C – DECEMBER 2001 – REVISED JANUARY 2010
DEVICE INFORMATION
REFOUT
REFIN
NC
NC
+AVDD
AGND
+IN
-IN
PBS PACKAGE
TQFP-32
(TOP VIEW)
32
31
30
29
28
27
26
25
DB13
3
22
RD
DB12
4
21
CONVST
DB11
5
20
CLOCK
DB10
6
19
DGND
DB9
7
18
+DVDD
DB8
8
17
BUSY
9
10
11
12
13
14
15
16
DB0
BYTE
DB1
23
DB2
2
DB3
DB14
DB4
CS
DB5
24
DB6
1
DB7
DB15
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ADS8323
SBAS224C – DECEMBER 2001 – REVISED JANUARY 2010
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PIN ASSIGNMENTS
TERMINAL
(1)
6
NO
NAME
I/O (1)
1
DB15
DO
Data Bit 15 (MSB)
2
DB14
DO
Data Bit 14
3
DB13
DO
Data Bit 13
4
DB12
DO
Data Bit 12
5
DB11
DO
Data Bit 11
6
DB10
DO
Data Bit 10
7
DB9
DO
Data Bit 9
8
DB8
DO
Data Bit 8
DESCRIPTION
9
DB7
DO
Data Bit 7
10
DB6
DO
Data Bit 6
11
DB5
DO
Data Bit 5
12
DB4
DO
Data Bit 4
13
DB3
DO
Data Bit 3
14
DB2
DO
Data Bit 2
15
DB1
DO
Data Bit 1
16
DB0
DO
Data Bit 0 (LSB)
17
BUSY
DO
High when a conversion is in progress.
18
+DVDD
P
Digital Power Supply, +5VDC.
19
DGND
P
Digital Ground
20
CLOCK
DI
An external CMOS-compatible clock can be applied to the CLOCK input to synchronize the
conversion process to an external source.
21
CONVST
DI
Convert Start
22
RD
DI
Synchronization pulse for the parallel output.
23
BYTE
DI
Selects eight most significant bits (low) or eight least significant bits (high). Data valid on pins
9-16.
24
CS
DI
Chip Select
25
–IN
AI
Inverting Input Channel
26
+IN
AI
Noninverting Input Channel
27
AGND
P
Analog Ground
28
+AVDD
P
Analog Power Supply, +5VDC.
29
NC
—
No connection
30
NC
—
No connection
31
REFIN
AI
Reference Input. When using the internal 2.5V reference, tie this pin directly to REFOUT.
32
REFOUT
AO
Reference Output. A 0.1μF capacitor should be connected to this pin when the internal
reference is used.
AI is analog input, AO is analog output, DI is digital input, DO is digital output, and P is power-supply connection.
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SBAS224C – DECEMBER 2001 – REVISED JANUARY 2010
TIMING INFORMATION
tC1
tW2
tW1
CLOCK
2
1
3
Acquisition
4
5
17
18
19
Conversion
Acquisition
tCONV
tACQ
20
1
2
3
4
17
18
19
20
tD1
CONVST
tW3
BUSY
tW4
tD2
tD4
BYTE
tD3
tW5
CS
tD5
tD6
tD9
tD8
tW7
tW6
RD
tD7
DB15-D8
Bits 15-8
Bits 15-8
FF
DB7-D0
Bits 7-0
Bits 7-0
Bits 15-8
TIMING CHARACTERISTICS (1) (2)
All specifications typical at –40°C to +85°C, +DVDD = +5V.
ADS8323
PARAMETER
TEST CONDITIONS
MIN
TYP
MAX
UNIT
1.6
μs
tCONV
Conversion Time
tAQC
Acquisition Time
350
ns
tC1
CLOCK Period
100
ns
tW1
CLOCK High Time
40
ns
tW2
CLOCK Low Time
40
ns
tD1
CONVST Low to Clock High
10
ns
tW3
CONVST Low Time
20
tD2
CONVST Low to BUSY High
tD3
CS Low to CONVST Low
0
tW4
CONVST High
20
tD4
CLOCK High to BUSY Low
tW5
CS High
0
ns
tD5
CS Low to RD Low
0
ns
tD6
RD High to CS High
0
ns
tW6
RD Low Time
50
ns
tD7
RD Low to Data Valid
40
ns
tD8
Data Hold from RD High
5
ns
tD9
BYTE Change to RD Low (3)
0
ns
tW7
RD High Time
20
ns
(1)
(2)
(3)
ns
25
ns
ns
ns
25
ns
All input signals are specified with rise and fall times of 5ns, tR = tF = 5ns (10% to 90% of DVDD) and timed from a voltage level of (VIL +
VIH) /2.
See timing diagram.
BYTE is asynchronous; when BYTE is '0', bits 15 through 0 appear at DB15-DB0. When BYTE is '1', bits 15 through 8 appear on
DB7-DB0. RD may remain low between changes in BYTE.
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ADS8323
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TYPICAL CHARACTERISTICS
At –40°C to +85°C, +DVDD = +AVDD = +5V, VREF = +2.5V, fSAMPLE = 500kSPS, and fCLK = 20 • fSAMPLE, unless otherwise
specified.
FREQUENCY SPECTRUM
(4096 Point FFT; fIN = 100.1kHz, –0.2dB)
SIGNAL-TO-NOISE RATIO AND
SIGNAL-TO-NOISE + DISTORTION vs INPUT FREQUENCY
0
90
SNR, SINAD (dB)
-30
Amplitude (dB)
-50
-70
-90
85
SNR
80
SINAD
-110
-130
75
0
25
50
75
1
100 125 150 175 200 225 250
10
Frequency (kHz)
Figure 1.
250
Figure 2.
SPURIOUS FREE DYNAMIC RANGE AND
TOTAL HARMONIC DISTORTION vs INPUT FREQUENCY
-100
95
-95
-90
SFDR
THD
85
-85
80
-80
0.3
22.9
0.2
15.3
0.1
7.6
0
75
-0.1
-40
-75
1
10
100
250
0
-7.6
-20
0
Frequency (kHz)
Figure 3.
INL– vs TEMPERATURE
60
80
100
DNL+ vs TEMPERATURE
3.8
0
0.25
19.1
0.15
11.4
0.05
3.8
-0.05
-3.8
-3.8
-0.10
-7.6
-0.15
-11.4
-0.20
-15.3
-40
-20
0
20
40
Temperature (°C)
60
80
100
-0.15
-40
-20
Figure 5.
0
20
40
Temperature (°C)
60
80
Delta (mV)
-0.05
Delta (LSB)
0
Delta (mV)
Delta (LSB)
20
40
Temperature (°C)
Figure 4.
0.05
8
Delta (mV)
90
INL+ vs TEMPERATURE
Delta (LSB)
100
THD (dB)
SFDR (dB)
100
Frequency (kHz)
-11.4
100
Figure 6.
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TYPICAL CHARACTERISTICS (continued)
At –40°C to +85°C, +DVDD = +AVDD = +5V, VREF = +2.5V, fSAMPLE = 500kSPS, and fCLK = 20 • fSAMPLE, unless otherwise
specified.
GAIN ERROR vs TEMPERATURE
762.9
0.4
30.5
8
610.4
0.2
15.3
6
457.8
4
305.2
2
152.6
0
0
0
Delta (LSB)
10
-0.2
-15.3
-0.4
-30.5
0
-45.8
-2
-0.6
Ð40
Ð20
0
20
40
Temperature (°C)
60
80
100
-152.6
-40
0
-20
20
40
Temperature (°C)
Figure 7.
80
100
IQ vs TEMPERATURE
2.0
26.2
1.0
13.1
0.8
0
0.4
-13.1
-2.0
-26.2
-3.0
-39.3
-4.0
-52.4
-5.0
-65.5
-6.0
-78.6
-7.0
-91.8
Delta (LSB)
-1.0
Delta (mA)
0
Delta (mV)
60
Figure 8.
VREF vs TEMPERATURE
0
-0.4
-0.8
-104.9
-8.0
-40
-20
0
20
40
60
80
-1.2
100
Temperature (°C)
-40
0
-20
Figure 9.
20
40
60
80
100
Figure 10.
BIPOLAR ZERO vs TEMPERATURE
POSITIVE FULL-SCALE vs TEMPERATURE
5.4
412.0
1.0
76.3
4.4
335.7
0.6
45.8
3.4
253.4
0.2
15.3
2.4
183.1
-0.2
-15.3
1.4
106.8
-0.6
-45.8
0.4
30.5
-1.0
-40
-20
0
20
40
Temperature (°C)
60
80
-76.3
100
Delta (LSB)
106.8
-0.6
-40
-20
Figure 11.
0
20
40
Temperature (°C)
60
80
Delta (mV)
1.4
Delta (mV)
Delta (LSB)
Delta (mV)
45.8
Delta (mV)
Delta (LSB)
DNL– vs TEMPERATURE
0.6
-45.8
100
Figure 12.
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TYPICAL CHARACTERISTICS (continued)
At –40°C to +85°C, +DVDD = +AVDD = +5V, VREF = +2.5V, fSAMPLE = 500kSPS, and fCLK = 20 • fSAMPLE, unless otherwise
specified.
LINEARITY ERROR AND
DIFFERENTIAL LINEARITY ERROR vs CODE
0
0
-1
-76.3
-2
-152.6
-3
-228.9
-4
-305.2
-5
-40
-381.5
-20
0
20
40
Temperature (°C)
60
80
100
INL (LSB)
76.3
DNL (LSB)
1
Delta (mV)
Delta (LSB)
NEGATIVE FULL-SCALE vs TEMPERATURE
4
3
2
1
0
-1
-2
-3
-4
2.5
2.0
1.5
1.0
0.5
0
-0.5
-1.0
-1.5
0000h 2000h 4000h 6000h 8000h A000h C000h E000h FFFFh
Decimal Code
Figure 13.
10
Figure 14.
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SBAS224C – DECEMBER 2001 – REVISED JANUARY 2010
THEORY OF OPERATION
The ADS8322 is a high-speed successive
approximation register (SAR) A/D converter with an
internal 2.5V bandgap reference that operates from a
single +5V supply. The input is fully differential with a
typical common-mode rejection of 70dB. The device
accepts a differential analog input voltage in the
range of –VREF to +VREF, centered on the
common-mode voltage (see the Analog Input
section). The device also accepts bipolar input ranges
when a level shift circuit is used at the front end (see
Figure 21). The basic operating circuit for the
ADS8323 is shown in Figure 15.
The ADS8323 requires an external clock to run the
conversion process. This clock can vary between
25kHz (1.25kHz throughput) and 10MHz (500kSPS
throughput). The duty cycle of the clock is
unimportant as long as the minimum high and low
times are at least 40ns and the clock period is at
least 100ns. The minimum clock frequency is
governed by the parasitic leakage of the Capacitive
Digital-to-Analog Converter (CDAC) capacitors
internal to the ADS8323.
white space here
+5V Analog Supply
10mF
+
0.1mF
0.1mF
+
Analog Input
32
31
30
29
28
27
26
25
REFOUT
REFIN
NC
NC
+AVDD
AGND
+IN
-IN
-
CS 24
1
DB15
2
DB14
BYTE 23
3
DB13
RD 22
4
DB12
CONVST 21
Chip Select
Read Input
Conversion Start
ADS8322
+DVDD 18
8
DB8
BUSY 17
DB0
DB9
DB1
7
DB2
DGND 19
DB3
DB10
DB4
6
DB5
CLOCK 20
DB6
DB11
DB7
5
9
10
11
12
13
14
15
16
Clock Input
Busy Output
Figure 15. Typical Circuit Configuration
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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. A conversion is initiated on
the ADS8323 by bringing CONVST (pin 21) low for a
minimum of 20ns. CONVST low places the
sample-and-hold amplifier in the hold state and the
conversion process is started. The BUSY output (pin
17) goes high when the conversion begins and stays
high during the conversion. While a conversion is in
progress, both inputs are disconnected from any
internal function. When the conversion result is
latched into the output register, the BUSY signal goes
low. The data can be read from the parallel output
bus following the conversion by bringing both RD and
CS low.
NOTE: This mode of operation is described in more
detail in the Timing and Control section of this data
sheet.
SAMPLE-AND-HOLD SECTION
The sample-and-hold on the ADS8323 allows the
ADC to accurately convert an input sine wave of
full-scale amplitude to 16-bit resolution. The input
bandwidth of the sample-and-hold is greater than the
Nyquist rate (Nyquist equals one-half of the sampling
rate) of the ADC even when the ADC is operated at
its maximum throughput rate of 500kSPS. The typical
small-signal bandwidth of the sample-and-hold
amplifier is 20MHz. The typical aperture delay time,
or the time it takes for the ADS8323 to switch from
the sample to the hold mode following the negative
edge of the CONVST signal, is 10ns. The average
delta of repeated aperture delay values is typically
30ps (also known as aperture jitter). These
specifications reflect the ability of the ADS8323 to
capture ac input signals accurately at the exact same
moment in time.
REFERENCE
If the internal reference is used, REFOUT (pin 32)
should be directly connected to REFIN (pin 31); see
Figure 15. The ADS8323 can operate, however, with
an external reference in the range of 1.5V to 2.55V
for a corresponding full-scale range of 3.0V to 5.1V.
The internal reference of the ADS8323 is
double-buffered. If the internal reference is used to
drive an external load, a buffer is provided between
the reference and the load applied to REFOUT (pin 32)
(the internal reference can typically source or sink
10μA of current; compensation capacitance should be
at least 0.1μF to minimize noise). If an external
reference is used, the second buffer provides
isolation between the external reference and the
CDAC. This buffer is also used to recharge all of the
capacitors of the CDAC during conversion.
ANALOG INPUT
The analog input is bipolar and fully differential. There
are two general methods of driving the analog input
of the ADS8323: single-ended or differential, as
shown in Figure 16 and Figure 17. When the input is
single-ended, the –IN input is held at the
common-mode voltage. The +IN input swings around
the same common voltage and the peak-to-peak
amplitude is the (common-mode + VREF) and the
(common-mode – VREF). The value of VREF
determines the range over which the common-mode
voltage may vary (see Figure 18).
-VREF to +VREF
peak-to-peak
ADS8323
Common
Voltage
Single-Ended Input
VREF
peak-to-peak
Common
Voltage
ADS8323
VREF
peak-to-peak
Differential Input
Figure 16. Methods of Driving the ADS8323: Single-Ended or Differential
12
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+IN
CM + VREF
+VREF
CM Voltage
-IN = CM Voltage
-VREF
t
CM - VREF
Single-Ended Inputs
+IN
CM + 1/2VREF
+VREF
CM Voltage
CM - 1/2VREF
-VREF
-IN
t
Differential Inputs
Common-Mode Voltage (Differential Mode) =
Note:
(+IN) + (-IN)
, Common-Mode Voltage (Single-Ended Mode) = IN-.
2
The maximum differential voltage between +IN and –IN of the ADS8323 is VREF. See Figure 18 and Figure 19 for a
further explanation of the common voltage range for single-ended and differential inputs.
Figure 17. Using the ADS8323 in the Single-Ended and Differential Input Modes
white space here
5
5
AVDD = 5V
4.55
AVDD = 5V
3
2.75
Single-Ended Input
2.25
2
1
4.025
4
3.8
Common Voltage Range (V)
Common Voltage Range (V)
4
1.2
3
Differential Input
2
0.975
1
0.45
0
0
-1
-1
1.0
1.5
2.0
2.55
2.5
3.0
1.0
1.5
2.0
2.55
2.5
3.0
VREF (V)
VREF (V)
Figure 18. Single-Ended Input: Common-Mode
Voltage Range vs VREF
Figure 19. Differential Input: Common-Mode
Voltage Range vs VREF
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ADS8323
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NOISE
R1
Figure 20 shows the transition noise of the ADS8323.
A low-level dc input was applied to the analog-input
pins and the converter was put through 8192
conversions. The digital output of the ADC varies in
output code due to the internal noise of the ADS8323.
This characteristic is true for all 16-bit SAR-type
ADCs. The ADS8323, with five output codes for the σ
distribution, yields a greater than ±0.8LSB transition
noise at 5V operation. Remember that to achieve this
low-noise performance, the peak-to-peak noise of the
input signal and reference must be less than 50μV.
4kW
Bipolar
Input
+IN (pin 26)
OPA132
-IN (pin 25)
ADS8323
R2
OPA353
BIPOLAR INPUT
±10V
±5V
±2.5V
5052
20kW
R1
R2
1kW
2kW
4kW
5kW
10kW
20kW
REFOUT (pin 32)
2.5V
Figure 21. Level Shift Circuit for Bipolar Input
Ranges
1968
54
0014
DIGITAL INTERFACE
818
TIMING AND CONTROL
0018
See the timing diagram and the Timing
Characteristics section for detailed information on
timing signals and the respective requirements for
each.
300
0015
0016
0017
Code
Figure 20. Histogram of 8,192 Conversions of a
Low-Level DC Input
AVERAGING
Averaging the digital codes can compensate the
noise of the ADC. 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 ±0.4LSB. 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 process works in a
similar manner to averaging—for every decimation by
2, the signal-to-noise ratio improves by 3dB.
BIPOLAR INPUTS
The differential inputs of the ADS8323 were designed
to accept bipolar inputs (–VREF and +VREF) around the
common-mode voltage, which corresponds to a 0V to
5V input range with a 2.5V reference. By using a
simple op amp circuit featuring four high-precision
external resistors, the ADS8323 can be configured to
accept bipolar inputs. The conventional ±2.5V, ±5V,
and ±10V input ranges could be interfaced to the
ADS8323 using the resistor values shown in
Figure 21.
14
The ADS8323 uses an external clock (CLOCK, pin
20) that controls the conversion rate of the CDAC.
With a 10MHz external clock, the ADC sampling rate
is 500kSPS that corresponds to a 2μs maximum
throughput time.
Conversions are initiated by bringing the CONVST
pin low for a minimum of 20ns (after the 20ns
minimum requirement has been met, the CONVST
pin can be brought high), while CS is low. The
ADS8322 switches from Sample-to-Hold mode on the
falling edge of the CONVST command. Following the
first rising edge of the external clock after a CONVST
low, the ADS8322 begins conversion (this first rising
edge of the external clock represents the start of
clock cycle one; the ADS8322 requires 16 rising clock
edges to complete a conversion). The BUSY output
goes high immediately following CONVST going low.
BUSY stays high through the conversion process and
returns low when the conversion has ended.
Both RD and CS can be high during and before a
conversion (although CS must be low when CONVST
goes low to initiate a conversion). Both the RD and
CS pins are brought low in order to enable the
parallel output bus with the conversion.
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EXPLANATION OF CLOCK, BUSY AND BYTE
PINS
CLOCK: An external clock must be provided for the
ADS8323. The maximum clock frequency is 10MHz
and that provides 500kSPS throughput. The minimum
clock frequency is 25kHz and that provides 1.25kHz
throughput. The minimum clock cycle is 100ns (see
Timing Diagram, tC1), and CLOCK must remain high
(see Timing Diagram, tW1) or low (see Timing
Diagram, tW2) for at least 40ns.
BUSY: Initially, BUSY output is low. Reading data
from output register or sampling the input analog
signal does not affect the state of the BUSY signal.
After the CONVST input goes low and conversion
starts, a maximum of 25ns later the BUSY output
goes high. That signal stays high during conversion
and provides the status of the internal ADC to the
DSP or μC. At the end of conversion, on the rising
edge of the 17th clock cycle, new data from the
internal ADC are latched into the output registers.
The BUSY signal goes low a maximum of 25ns later
(see Timing Diagram, tD4).
BYTE: The output data appear as a full 16-bit word
on DB15-DB0 (MSB-LSB or D15-D0) if BYTE is low.
If there is only an 8-bit bus available on a board, the
result may also be read on an 8-bit bus by using only
DB7-DB0. In this case, two reads are necessary (see
the timing diagram). The first, as before, leaving
BYTE low and reading the eight least significant bits
on DB7-DB0, then bringing BYTE high. When BYTE
is high, the upper eight bits (D15-D8) appear on
DB7-DB0.
START OF A CONVERSION AND READING DATA
By bringing the CONVST signal low, the input data
are immediately placed in the hold mode (10ns),
although CS must be low when CONVST goes low to
initiate a conversion. The conversion follows with the
next rising edge of CLOCK. If it is important to detect
a hold command during a certain clock cycle, then
the falling edge of the CONVST signal must occur at
least 10ns before the rising edge of CLOCK (see
Timing Diagram, tD1). The CONVST signal can
remain low without initiating a new conversion. The
CONVST signal must be high for at least 20ns (see
Timing Diagram, tW4) before it is brought low again
and CONVST must stay low for at least 20ns (see
Timing Diagram, tW3). Once a CONVST signal goes
low, further impulses of this signal are ignored until
the conversion is finished or the device is reset.
When the conversion is finished (after 16 clock
cycles) the sampling switches close and sample the
new value. The start of the next conversion must be
delayed to allow the input capacitor of the ADS8323
to be fully charged. This delay time depends on the
driving amplifier, but should be at least 400ns. To
gain acquisition time, the falling edge of CONVST
must take place just before the rising edge of CLOCK
(see Timing Diagram, tD1). One conversion cycle
requires 20 clock cycles. However, reading data
during the conversion or on a falling hold edge may
cause a loss in performance.
Reading Data (RD, CS): In general, the data outputs
are in 3-state. Both CS and RD must be low to
enable these outputs. RD and CS must stay low
together for at least 40ns (see Timing Diagram, tD7)
before the output data is valid. RD must remain high
for at least 20ns (see Timing Diagram, tW7) before
bringing it back low for a subsequent read command.
16 clock-cycles after the start of a conversion (that is,
the next rising edge of the clock after the falling edge
of CONVST), the new data are latched into the output
register and the reading process can start again.
Refer to Table 1 for ideal output codes.
CS being low tells the ADS8323 that the bus on the
board is assigned to the ADS8323. If an ADC shares
a bus with digital gates, there is a possibility that
digital (high-frequency) noise could get coupled into
the ADC. If the bus is just used by the ADS8323, CS
can be hard-wired to ground. The output data should
not be read 125ns prior to the falling edge of
CONVST and 10ns after the falling edge.
The ADS8323 output is in binary twos complement
format (see Figure 22).
Table 1. Ideal Input Voltages and Output Codes
DESCRIPTION
DIGITAL OUTPUT
BINARY TWOS COMPLEMENT
ANALOG VALUE
Full-Scale Range
2 • VREF
Least Significant Bit (LSB)
2 • VREF/65535
BINARY CODE
HEX CODE
+Full Scale
+VREF – 1 LSB
0111 1111 1111 1111
7FFF
Midscale
0V
0000 0000 0000 0000
0000
Midscale – 1 LSB
0V – 1 LSB
1111 1111 1111 1111
FFFF
Zero
–VREF
1000 0000 0000 0000
8000
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ADS8323
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LAYOUT
For optimum performance, care should be taken with
the physical layout of the ADS8323 circuitry. This
consideration is particularly true if the CLOCK input is
approaching the maximum throughput rate.
As the ADS8323 offers single-supply operation, it is
often used in close proximity with digital logic,
microcontrollers, microprocessors, and digital signal
processors. The more digital logic present in the
design and the higher the switching speed, the more
difficult it is to achieve good performance from the
converter.
The basic SAR architecture is sensitive to glitches or
sudden changes on the power supply, reference,
ground connections and digital inputs that occur just
before latching the output of the analog comparator.
Thus, during any single conversion for an n-bit SAR
converter, there are n windows in which large
external transient voltages can affect the conversion
result. Such glitches might originate from switching
power supplies, or nearby digital logic or high-power
devices.
The degree of error in the digital output depends on
the reference voltage, layout, and the exact timing of
the external event. These errors can change if the
external event changes in time with respect to the
CLOCK input.
16
On average, the ADS8323 draws very little current
from an external reference, as the reference voltage
is internally buffered. If the reference voltage is
external and originates from an op amp, make sure
that it can drive the bypass capacitor or capacitors
without oscillation. A 0.1μF bypass capacitor is
recommended from pin 31 directly to ground.
The AGND and DGND pins should be connected to a
clean ground point. In all cases, this point should be
the analog ground. Avoid connections which are too
close to the grounding point of a microcontroller or
digital signal processor. If required, run a ground
trace directly from the converter to the power supply
entry point. The ideal layout includes an analog
ground plane dedicated to the converter and
associated analog circuitry.
As with the GND connections, VDD should be
connected to a +5V power supply plane, or trace, that
is separate from the connection for digital logic until
they are connected at the power entry point. Power to
the ADS8323 should be clean and well-bypassed. A
0.1μF ceramic bypass capacitor should be placed as
close to the device as possible. In addition, a 1μF to
10μF capacitor is recommended. If needed, an even
larger capacitor and a 5Ω or 10Ω series resistor may
be used to low-pass filter a noisy supply. In some
situations, additional bypassing may be required,
such as a 100μF electrolytic capacitor, or even a Pi
filter made up of inductors and capacitors all
designed to essentially low-pass filter the +5V supply,
removing the high-frequency noise.
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0111 1111 1111 1111
65535
0111 1111 1111 1110
65534
0111 1111 1111 1101
65533
0000 0000 0000 0001
32769
0000 0000 0000 0000
32768
1111 1111 1111 1111
32767
1000 0000 0000 0010
Step
Digital Output Code
Binary Twos
Complement
(BTC)
2
1000 0000 0000 0001
1
1000 0000 0000 0000
0
2.499962V
VNFS = VCM - VREF = 0V
0.000038V
2.500038V
VPFS = VCM + VREF = 5V
VPFS Ð 1LSB = 4.999924V
VBPZ = 2.5V
0.000076V
4.999848V
Unipolar Analog Input Voltage
1LSB = 76mV
0.000152V
VCM = 2.5V
16-BIT
Bipolar Input, Binary Twos Complement Output: (BTC)
Negative Full-Scale Code = VNFS = 8000h, Vcode = VCM - VREF
Bipolar Zero Code = VBPZ = 0000h, Vcode = VCM
Positive Full-Scale Code = VPFS = 7FFFh, Vcode = (VCM + VREF) - 1LSB
VREF = 2.5V
Figure 22. Ideal Conversion Characteristics (Condition: Single-Ended, VCM = IN– = 2.5V, VREF = 2.5V)
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ADS8323
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REVISION HISTORY
NOTE: Page numbers for previous revisions may differ from page numbers in the current version.
Changes from Original (May, 2002) to Revision C
Page
•
Updated document format to current standards ................................................................................................................... 1
•
Deleted lead temperature specifications from Absolute Maximum Ratings table ................................................................ 2
•
Changed conversion time from 1.6μs (min) to 1.6μs (max) ................................................................................................. 3
•
Changed acquisition time specification from .4μs (max) to 350ns (min) .............................................................................. 3
•
Changed acquisition time specification from .4μs (max) to 350ns (min) .............................................................................. 7
18
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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)
ADS8323Y/250
ACTIVE
TQFP
PBS
32
250
RoHS & Green
Call TI
Level-3-260C-168 HR
-40 to 85
A23Y
Samples
ADS8323Y/2K
ACTIVE
TQFP
PBS
32
2000
RoHS & Green
Call TI
Level-3-260C-168 HR
-40 to 85
A23Y
Samples
ADS8323YB/250
ACTIVE
TQFP
PBS
32
250
RoHS & Green
Call TI
Level-3-260C-168 HR
-40 to 85
A23Y
B
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
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