ADS7822
AD
S78
22
AD
S
7822
SBAS062C – JANUARY 1996 – REVISED AUGUST 2007
12-Bit, 200kHz, microPower Sampling
ANALOG-TO-DIGITAL CONVERTER
FEATURES
1
DESCRIPTION
• 200kHz Sampling Rate
• microPower:
1.6mW at 200kHz
0.54mW at 75kHz
0.06mW at 7.5kHz
• Power Down: 3μA max
• Mini-DIP-8, SO-8, and MSOP-8 Packages
• Pseudo-Differential Input
• Serial Interface
2
The ADS7822 is a 12-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 200kHz rate. At
lower conversion rates, the high speed of the device
enables it to spend most of its time in the
power-down mode—the power dissipation is less
than 60μW at 7.5kHz.
APPLICATIONS
•
•
•
•
Battery-Operated Systems
Remote Data Acquisition
Isolated Data Acquisition
Simultaneous Sampling, Multichannel Systems
The ADS7822 also features operation from 2.0V to
5V, a synchronous serial interface, and a
pseudo-differential input. The reference voltage can
be set to any level within the range of 50mV to VCC.
Ultra low power and small size make the ADS7822
ideal for battery-operated systems. It is also a perfect
fit for remote data-acquisition modules, simultaneous
multichannel systems, and isolated data acquisition.
The ADS7822 is available in a plastic mini-DIP-8, an
SO-8, or an MSOP-8 package.
Control
SAR
VREF
DOUT
+In
Serial
Interface
CDAC
-In
S/H Amp
Comparator
DCLOCK
CS/SHDN
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 © 1996–2007, Texas Instruments Incorporated
ADS7822
www.ti.com
SBAS062C – JANUARY 1996 – REVISED AUGUST 2007
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)
MAXIMUM
DIFFERENTIAL
LINEARITY
ERROR
(LSB)
PACKAGELEAD
PACKAGE
DESIGNATOR
SPECIFIED
TEMPERATURE
RANGE
PACKAGE
MARKING (2)
ADS7822E
±2
±2
MSOP-8
DGK
–40°C to +85°C
A22
ADS7822EB
ADS7822EC
±1
±0.75
±1
±0.75
MSOP-8
MSOP-8
DGK
DGK
–40°C to +85°C
ORDERING
NUMBER
TRANSPORT
MEDIA,
QUANTITY
ADS7822E/250
Tape and Reel,
250
ADS7822E/2K5
Tape and Reel,
2500
ADS7822EB/250
Tape and Reel,
250
ADS7822EB/2K5
Tape and Reel,
2500
ADS7822EC/250
Tape and Reel,
250
ADS7822EC/2K5
Tape and Reel,
2500
A22
–40°C to +85°C
A22
ADS7822P
±2
±2
Plastic
DIP-8
P
–40°C to +85°C
ADS7822P
ADS7822P
Rails, 50
ADS7822PB
±1
±1
Plastic
DIP-8
P
–40°C to +85°C
ADS7822PB
ADS7822PB
Rails, 50
ADS7822PC
±0.75
±0.75
Plastic
DIP-8
P
–40°C to +85°C
ADS7822PC
ADS7822PC
Rails, 50
ADS7822U
±2
±2
SO-8
D
–40°C to +85°C
ADS7822U
ADS7822UB
±1
±1
SO-8
D
–40°C to +85°C
ADS7822UB
ADS7822UC
±0.75
±0.75
SO-8
D
–40°C to +85°C
ADS7822UC
(1)
(2)
ADS7822U
Rails, 100
ADS7822U/2K5
Tape and Reel,
2500
ADS7822UB
Rails, 100
ADS7822UB/2K5
Tape and Reel,
2500
ADS7822UC
Rails, 100
ADS7822UC/2K5
Tape and Reel,
2500
For the most current package and ordering information, see the Package Option Addendum located at the end of this data sheet, or see
the TI website at www.ti.com.
Performance grade information is marked on the reel.
ABSOLUTE MAXIMUM RATINGS (1)
over operating free-air temperature range (unless otherwise noted)
ADS7822
UNIT
+6
V
–0.3 to VCC + 0.3
V
VCC
Analog input
Logic input
–0.3 to 6
V
Case temperature
+100
°C
Junction temperature
+150
°C
Storage temperature
+125
°C
External reference voltage
+5.5
V
(1)
2
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 © 1996–2007, Texas Instruments Incorporated
Product Folder Link(s): ADS7822
ADS7822
www.ti.com
SBAS062C – JANUARY 1996 – REVISED AUGUST 2007
ELECTRICAL CHARACTERISTICS: +VCC = +2.7V
At –40°C to +85°C, +VCC = +2.7V, VREF = +2.5V, fSAMPLE = 75kHz, and fCLK = 16 × fSAMPLE, unless otherwise noted.
ADS7822
PARAMETER
ADS7822B
ADS7822C
TEST CONDITIONS
UNIT
MIN
TYP
MAX
MIN
TYP
MAX
MIN
TYP
MAX
ANALOG INPUT
Full-scale input span
+In – (–In)
0
VREF
0
VREF
0
VREF
V
+In – GND
–0.2
VCC + 0.2
–0.2
VCC + 0.2
–0.2
VCC + 0.2
V
–In – GND
–0.2
+1.0
–0.2
+1.0
–0.2
+1.0
Absolute input range
V
Capacitance
25
25
25
pF
Leakage current
±1
±1
±1
μA
12
Bits
SYSTEM PERFORMANCE
Resolution
12
12
No missing codes
11
12
11
Integral linearity error
–2
±0.5
+2
–1
±0.5
+1
–0.75
±0.25
+0.75
LSB (1)
Bits
Differential linearity error
–2
±0.5
+2
–1
±0.5
+1
–0.75
±0.25
+0.75
LSB
Offset error
–3
+3
–3
+3
–1
+1
LSB
Gain error
–3
+3
–3
+3
–1
+1
LSB
Noise
33
33
33
μVrms
Power-supply rejection
82
82
82
dB
SAMPLING DYNAMICS
Conversion time
12
Acquisition time
1.5
12
1.5
Throughput rate
12
1.5
75
Clk Cycles
Clk Cycles
75
75
kHz
DYNAMIC CHARACTERISTICS
Total harmonic distortion
VIN = 2.5VPP at 1kHz
–82
–82
–82
dB
SINAD
VIN = 2.5VPP at 1kHz
71
71
71
dB
Spurious-free dynamic range
VIN = 2.5VPP at 1kHz
86
86
86
dB
REFERENCE OUTPUT
Voltage range
0.05
Resistance
Current drain
VCC
CS = GND, fSAMPLE = 0Hz
5
CS = VCC
5
At code 710h
8
fSAMPLE = 7.5kHz
0.05
VCC
8
0.001
8
0.001
GΩ
40
0.001
μA
μA
0.8
3
V
GΩ
5
40
0.8
3
VCC
5
5
40
0.8
CS = VCC
0.05
5
3
μA
DIGITAL INPUT/OUTPUT
Logic family
Logic levels
CMOS
CMOS
CMOS
VIH
IIH = +5μA
2.0
5.5
2.0
5.5
2.0
5.5
V
VIL
IIL = +5μA
–0.3
0.8
–0.3
0.8
–0.3
0.8
V
VOH
IOH = –250μA
VOL
IOL = 250μA
2.1
2.1
2.1
0.4
Data format
V
0.4
Straight Binary
Straight Binary
0.4
V
Straight Binary
POWER-SUPPLY REQUIREMENTS
Specified performance
VCC
See Notes
See Note
Quienscent current
Power down
(2)
and
(3)
(3)
2.7
3.6
2.7
3.6
2.7
3.6
V
2.0
2.7
2.0
2.7
2.0
2.7
V
2.7
3.6
2.7
3.6
2.7
3.6
fSAMPLE = 7.5kHz (4) (5)
20
fSAMPLE = 75kHz (5)
200
CS = VCC
20
325
200
3
325
200
3
V
μA
20
325
μA
3
μA
+85
°C
TEMPERATURE RANGE
Specified performance
(1)
(2)
(3)
(4)
(5)
–40
+85
–40
+85
–40
LSB means least significant bit. With VREF equal to +2.5V, one LSB is 0.61mV.
The maximum clock rate of the ADS7822 is less than 1.2MHz in this power-supply range.
See the Typical Characteristics for more information.
fCLK = 1.2MHz, CS = VCC for 145 clock cycles out of every 160.
See the Power Dissipation section for more information regarding lower sample rates.
Submit Documentation Feedback
Copyright © 1996–2007, Texas Instruments Incorporated
Product Folder Link(s): ADS7822
3
ADS7822
www.ti.com
SBAS062C – JANUARY 1996 – REVISED AUGUST 2007
ELECTRICAL CHARACTERISTICS: +VCC = +5V
At –40°C to +85°C, +VCC = +5V, VREF = +5V, fSAMPLE = 200kHz, and fCLK = 16 × fSAMPLE, unless otherwise noted.
ADS7822
PARAMETER
ADS7822B
TEST CONDITIONS
UNIT
MIN
TYP
MAX
MIN
TYP
MAX
ANALOG INPUT
Full-scale input span
+In – (–In)
0
VREF
0
VREF
V
+In – GND
–0.2
VCC + 0.2
–0.2
VCC + 0.2
V
–In – GND
–0.2
+1.0
–0.2
+1.0
Absolute input range
V
Capacitance
25
25
pF
Leakage current
±1
±1
μA
12
Bits
SYSTEM PERFORMANCE
Resolution
12
No missing codes
11
Integral linearity error
–2
Differential linearity error
12
+2
±0.8
Bits
–1
–1
±0.5
+1
LSB (1)
+1
LSB
Offset error
–3
+3
–3
+3
LSB
Gain error
–4
+4
–3
+3
LSB
Noise
33
33
μVrms
Power-supply rejection
70
70
dB
SAMPLING DYNAMICS
Conversion time
12
Acquisition time
1.5
12
1.5
Throughput rate
Clk Cycles
Clk Cycles
200
200
kHz
DYNAMIC CHARACTERISTICS
Total harmonic distortion
VIN = 5VPP at 10kHz
–78
–78
dB
SINAD
VIN = 5VPP at 10kHz
71
71
dB
Spurious-free dynamic range
VIN = 5VPP at 10kHz
79
79
dB
REFERENCE OUTPUT
Voltage range
0.05
CS = GND, fSAMPLE = 0Hz
Resistance
CS = VCC
Current drain
VCC
0.05
5
5
At code 710h
40
fSAMPLE = 12.5kHz
2.5
CS = VCC
0.001
VCC
5
5
100
40
GΩ
100
0.001
μA
μA
2.5
3
V
GΩ
3
μA
DIGITAL INPUT/OUTPUT
Logic family
CMOS
Logic levels
CMOS
VIH
IIH = +5μA
3.0
5.5
3.0
5.5
V
VIL
IIL = +5μA
–0.3
0.8
–0.3
0.8
V
VOH
IOH = –250μA
VOL
IOL = 250μA
3.5
3.5
V
0.4
Data format
0.4
Straight Binary
V
Straight Binary
POWER-SUPPLY REQUIREMENTS
VCC
Specified performance
Quienscent current
fSAMPLE = 200kHz
Power down
CS = VCC
4.75
5.25
320
4.75
550
320
3
5.25
V
550
μA
3
μA
+85
°C
TEMPERATURE RANGE
Specified performance
(1)
4
–40
+85
–40
LSB means least significant bit. With VREF equal to +5V, one LSB is 1.22mV.
Submit Documentation Feedback
Copyright © 1996–2007, Texas Instruments Incorporated
Product Folder Link(s): ADS7822
ADS7822
www.ti.com
SBAS062C – JANUARY 1996 – REVISED AUGUST 2007
PIN CONFIGURATION
D, DGK, OR P PACKAGE
SO, MSOP, or DIP
(TOP VIEW)
VREF
1
+In
2
8
+VCC
7
DCLOCK
ADS7822
-In
3
6
DOUT
GND
4
5
CS/SHDN
PIN ASSIGNMENTS
PIN
NAME
DESCRIPTION
NO.
VREF
1
Reference input
+In
2
Noninverting input
–In
3
Inverting input. Connect to ground or to remote ground sense point.
GND
4
Ground
CS/SHDN
5
Chip select when low; Shutdown mode when high.
DOUT
6
The serial output data word is comprised of 12 bits of data. In operation, the data are 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 are valid for the next edges.
DCLOCK
7
Data clock synchronizes the serial data transfer and determines conversion speed.
+VCC
8
Power supply
Submit Documentation Feedback
Copyright © 1996–2007, Texas Instruments Incorporated
Product Folder Link(s): ADS7822
5
ADS7822
www.ti.com
SBAS062C – JANUARY 1996 – REVISED AUGUST 2007
TYPICAL CHARACTERISTICS
At TA = +25°C, VCC = +2.7V, VREF = +2.5V, fSAMPLE = 75kHz, fCLK = 16 × fSAMPLE, unless otherwise specified.
DIFFERENTIAL LINEARITY ERROR
vs CODE
1.00
1.00
0.75
0.75
Differential Linearity Error (LSB)
Integral Linearity Error (LSB)
INTEGRAL LINEARITY ERROR
vs CODE
0.50
0.25
0.00
-0.25
-0.50
-0.75
-1.00
0.50
0.25
0.00
-0.25
-0.50
-0.75
-1.00
0
2048
4095
0
2048
4095
Code
Figure 1.
Figure 2.
SUPPLY CURRENT
vs TEMPERATURE
POWER-DOWN SUPPLY CURRENT
vs TEMPERATURE
350
120
300
100
Supply Current (nA)
Supply Current (mA)
Code
250
200
150
100
80
60
40
20
50
0
-50
0
-25
25
50
75
100
-50
0
-25
25
50
75
Temperature (°C)
Temperature (°C)
Figure 3.
Figure 4.
QUIESCENT CURRENT
vs VCC
MAXIMUM SAMPLE RATE
vs VCC
400
100
1000
Sample Rate (kHz)
Quiescent Current (mA)
350
300
250
200
100
10
150
100
1
1
2
3
4
5
1
VCC (V)
3
4
5
VCC (V)
Figure 5.
6
2
Figure 6.
Submit Documentation Feedback
Copyright © 1996–2007, Texas Instruments Incorporated
Product Folder Link(s): ADS7822
ADS7822
www.ti.com
SBAS062C – JANUARY 1996 – REVISED AUGUST 2007
TYPICAL CHARACTERISTICS (continued)
At TA = +25°C, VCC = +2.7V, VREF = +2.5V, fSAMPLE = 75kHz, fCLK = 16 × fSAMPLE, unless otherwise specified.
CHANGE IN OFFSET
vs REFERENCE VOLTAGE
CHANGE IN OFFSET
vs TEMPERATURE
1.2
0.6
VCC = 5V
0.4
0.8
Delta from 25°C (LSB)
Change in Offset (LSB)
1.0
0.6
0.4
0.2
0.0
-0.2
-0.4
0.2
0
-0.2
-0.4
-0.6
-0.6
-0.8
1
2
3
Reference Voltage (V)
4
5
-50
0
25
50
75
100
75
100
Temperature (°C)
Figure 7.
Figure 8.
CHANGE IN GAIN
vs REFERENCE VOLTAGE
CHANGE IN GAIN
vs TEMPERATURE
2.5
0.15
V
= 5V
VCC
CC = 5V
2.0
0.10
1.5
Delta from 25°C (LSB)
Change in Gain (LSB)
-25
1.0
0.5
0.0
-0.5
0.05
0
-0.05
-0.10
-1.0
-0.15
-1.5
1
2
3
Reference Voltage (V)
4
-50
5
0
25
50
Temperature (°C)
Figure 9.
Figure 10.
EFFECTIVE NUMBER OF BITS
vs REFERENCE VOLTAGE
PEAK-TO-PEAK NOISE
vs REFERENCE VOLTAGE
12.00
10
VCC = 5V
11.75
VCC = 5V
9
Peak-to-Peak Noise (LSB)
Effective Number of Bits (rms)
-25
11.50
11.25
11.00
10.75
10.50
10.25
8
7
6
5
4
3
2
1
10.00
0
0.1
1
10
0.1
Reference Voltage (V)
1
10
Reference Voltage (V)
Figure 11.
Figure 12.
Submit Documentation Feedback
Copyright © 1996–2007, Texas Instruments Incorporated
Product Folder Link(s): ADS7822
7
ADS7822
www.ti.com
SBAS062C – JANUARY 1996 – REVISED AUGUST 2007
TYPICAL CHARACTERISTICS (continued)
At TA = +25°C, VCC = +2.7V, VREF = +2.5V, fSAMPLE = 75kHz, fCLK = 16 × fSAMPLE, unless otherwise specified.
SPURIOUS FREE DYNAMIC RANGE AND
SIGNAL-TO-NOISE RATIO vs FREQUENCY
TOTAL HARMONIC DISTORTION
vs FREQUENCY
100
0
Spurious Free Dynamic Range
SFDR and SNR (dB)
80
70
60
Signal-to-Noise Ratio
50
-10
Total Harmonic Distortion (dB)
90
40
30
20
-20
-30
-40
-50
-60
-70
-80
10
-90
0
-100
1
10
100
Figure 14.
SIGNAL-TO-(NOISE+DISTORTION)
vs FREQUENCY
SIGNAL-TO-(NOISE+DISTORTION)
vs INPUT LEVEL
90
80
70
60
50
40
30
20
10
0
1
10
80
70
60
50
40
30
20
10
0
100
-40
-35
-30
-25
-20
-15
-10
-5
Frequency (kHz)
Input Level (dB)
Figure 15.
Figure 16.
REFERENCE CURRENT
vs SAMPLE RATE
REFERENCE CURRENT vs TEMPERATURE
(Code = 710h)
14
12
12
Reference Current (A)
14
10
8
6
4
0
10
8
6
4
2
2
0
0
15
30
45
60
75
-50
Sample Rate (kHz)
-25
0
25
50
75
100
Temperature (°C)
Figure 17.
8
100
Figure 13.
Signal-to-(Noise Ratio + Distortion) (dB)
Signal-to-(Noise + Distortion) (dB)
10
Frequency (kHz)
100
Reference Current (mA)
1
Frequency (kHz)
Figure 18.
Submit Documentation Feedback
Copyright © 1996–2007, Texas Instruments Incorporated
Product Folder Link(s): ADS7822
ADS7822
www.ti.com
SBAS062C – JANUARY 1996 – REVISED AUGUST 2007
TYPICAL CHARACTERISTICS (continued)
At TA = +25°C, VCC = +2.7V, VREF = +2.5V, fSAMPLE = 75kHz, fCLK = 16 × fSAMPLE, unless otherwise specified.
POWER-SUPPLY REJECTION
vs RIPPLE FREQUENCY
0
-10
-20
POWER-SUPPLY REJECTION
vs RIPPLE FREQUENCY
0
VCC = 2.7V
Ripple = 500mVPP
VIN = 1.25VDC
VREF = 2.5V
-10
-20
-30
PSR (dB)
PSR (dB)
-30
VCC = 5V
Ripple = 500mVPP
VIN = 2.5VDC
VREF = 5V
-40
-50
-60
-40
-50
-60
-70
-70
PSR (dB) = 20log(500mV/DVO)
where DVO = change in digital result
-80
-90
1k
10k
100k
1M
PSR (dB) = 20log(500mV/DVO)
where DVO = change in digital result
-80
-90
10M
10
1
1k
10k
100k
Ripple Frequency (Hz)
Ripple Frequency (Hz)
Figure 19.
Figure 20.
1M
10M
CHANGE IN INTEGRAL LINEARITY
AND DIFFERENTIAL LINEARITY
vs REFERENCE VOLTAGE
Delta from +2.5V Reference (LSB)
0.20
VCC = 5V
0.15
Change in Integral
Linearity (LSB)
0.10
0.05
0.00
Change in Differential
Linearity (LSB)
-0.05
-0.10
1
2
3
4
5
Reference Voltage (V)
Figure 21.
Submit Documentation Feedback
Copyright © 1996–2007, Texas Instruments Incorporated
Product Folder Link(s): ADS7822
9
ADS7822
www.ti.com
SBAS062C – JANUARY 1996 – REVISED AUGUST 2007
THEORY OF OPERATION
The ADS7822 is a classic successive approximation
register (SAR) A/D converter. The architecture is
based on capacitive redistribution that inherently
includes a sample/hold function. The converter is
fabricated on a 0.6μ CMOS process. The architecture
and process allow the ADS7822 to acquire and
convert an analog signal at up to 200,000
conversions per second while consuming very little
power.
The ADS7822 requires an external reference, an
external clock, and a single power source (VCC). The
external reference can be any voltage between 50mV
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
ADS7822.
The external clock can vary between 10kHz (625Hz
throughput) and 3.2MHz (200kHz throughput). The
duty cycle of the clock is essentially unimportant as
long as the minimum high and low times are at least
400ns for a supply range between 2.7V to 3.6V, or
125ns for a supply range between 4.75V to 5.25V.
The minimum clock frequency is set by the leakage
on the capacitors internal to the ADS7822.
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 ADS7822 after the
conversion is complete and to obtain the serial data
least significant bit first. See the Digital Interface
section for more information.
The range of the –In input is limited to –0.2V to +1V.
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 ADS7822 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
(25pF) to a 12-bit settling level within 1.5 clock
cycles. When the converter goes into the hold mode
or while it is in the power-down 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 –
200mV or exceed GND + 1V. The +In input should
always remain within the range of GND – 200mV to
VCC + 200mV. Outside of these ranges, the converter
linearity may not meet specifications.
REFERENCE INPUT
The external reference sets the analog input range.
The ADS7822 operates with a reference in the range
of 50mV 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 LSB (least significant
bit) size and is equal to the reference voltage divided
by 4096. 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.
ANALOG INPUT
The +In and –In input pins allow for a
pseudo-differential input signal. Unlike some
converters of this type, the –In input is not resampled
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.
10
Submit Documentation Feedback
Copyright © 1996–2007, Texas Instruments Incorporated
Product Folder Link(s): ADS7822
ADS7822
www.ti.com
SBAS062C – JANUARY 1996 – REVISED AUGUST 2007
DIGITAL INTERFACE
The noise inherent in the converter will also appear to
increase with lower LSB size. With a 2.5V reference,
the internal noise of the converter typically contributes
only 0.32 LSB peak-to-peak of potential error to the
output code. When the external reference is 50mV,
the potential error contribution from the internal noise
will be 50 times larger—16 LSBs. The errors due to
the internal noise are gaussian in nature and can be
reduced by averaging consecutive conversion results.
Signal Levels
The digital inputs of the ADS7822 can accommodate
logic levels up to 6V regardless of the value of VCC.
Thus, the ADS7822 can be powered at 3V and still
accept inputs from logic powered at 5V.
The CMOS digital output (DOUT) will swing 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.
For more information regarding noise, consult the
typical characteristic curves Effective Number of Bits
vs Reference Voltage and Peak-to-Peak Noise vs
Reference Voltage. Note that the effective number of
bits (ENOB) figure is calculated based on the
converter signal-to-(noise + distortion) ratio with a
1kHz, 0dB input signal. SINAD is related to ENOB as
follows:
Serial Interface
The ADS7822 communicates with microprocessors
and other digital systems via a synchronous 3-wire
serial interface, as shown in Figure 22 and Table 1.
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.
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 will also be more
sensitive to external sources of error such as nearby
digital signals and electromagnetic interference.
tCYC
CS/SHDN
Power
Down
tSUCS
DCLOCK
tCSD
DOUT
Hi-Z
Null
Bit
B11 B10 B9
B8
(MSB)
tSMPL
B7
B6
B5
B4
B3
B2
B1 B0
tCONV
Null
Bit
Hi-Z
(1)
B11 B10
B9
B8
tDATA
Note: (1) After completing the data transfer, if further clocks are applied with CS LOW,
the A/D will output LSB-First data then followed with zeroes indefinitely.
tCYC
CS/SHDN
tSUCS
Power Down
DCLOCK
tCSD
DOUT
Hi-Z
tSMPL
Null
Bit
Hi-Z
B11 B10 B9
(MSB)
B8
B7
B6
B5
B4
B3
B2
B1
B0
B1
B2
B3
tCONV
B4
B5
B6
B7
B8
B9 B10 B11
(1)
tDATA
Note: (1) After completing the data transfer, if further clocks are applied with CS LOW,
the A/D will output zeroes indefinitely.
tDATA: During this time, the bias current and the comparator power down and the reference input
becomes a high impedance node, leaving the CLK running to clock out LSB-first data or zeroes.
Figure 22. Basic Timing Diagrams
Submit Documentation Feedback
Copyright © 1996–2007, Texas Instruments Incorporated
Product Folder Link(s): ADS7822
11
ADS7822
www.ti.com
SBAS062C – JANUARY 1996 – REVISED AUGUST 2007
Table 1. Timing Specifications (–40°C to +85°C)
SYMBOL
VCC = 2.7V
DESCRIPTION
MIN
TYP
1.5
VCC = 5V
MAX
MIN
2.0
1.5
TYP
MAX
2.0
UNITS
tSMPL
Analog input sample time
tCONV
Conversion time
tCYC
Cycle time
tCSD
CS falling to DCLOCK low
tSUCS
CS falling to DCLOCK rising
thDO
DCLOCK falling to current DOUT not valid
tdDO
DCLOCK falling to next DOUT valid
130
200
85
150
ns
tdis
CS rising to DOUT tri-state
40
80
25
50
ns
ten
DCLOCK falling to DOUT enabled
75
175
50
100
ns
tf
DOUT fall time
90
200
70
100
ns
tr
DOUT rise time
110
200
60
100
ns
12
Clk Cycles
12
16
Clk Cycles
16
Clk Cycles
0
0.03
1000
0.03
15
0
ns
1000
μs
15
ns
1.4V
3kW
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
3kW
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
2
tdis
DOUT
Waveform 2(2)
10%
VOL
DOUT
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 23. Timing Diagrams and Test Circuits for the Parameters in Table 1
12
Submit Documentation Feedback
Copyright © 1996–2007, Texas Instruments Incorporated
Product Folder Link(s): ADS7822
ADS7822
www.ti.com
SBAS062C – JANUARY 1996 – REVISED AUGUST 2007
A falling CS signal initiates the conversion and data
transfer. The first 1.5 to 2.0 clock periods of the
conversion cycle are used to sample the input signal.
After the second falling DCLOCK edge, DOUT is
enabled and outputs a low value for one clock period.
For the next 12 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 (B11) has been repeated, DOUT will
tri-state. Subsequent clocks have no effect on the
converter. A new conversion is initiated only when CS
is taken high and returned low.
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.
Figure 24 shows the current consumption of the
ADS7822 versus sample rate. For this graph, the
converter is clocked at 1.2MHz regardless of the
sample rate—CS is high for the remaining sample
period. Figure 25 also shows current consumption
versus sample rate. However, in this case, the
DCLOCK period is 1/16th of the sample period—CS
is high for one DCLOCK cycle out of every 16.
1000
Data Format
Table 2. Ideal Input Voltages and Output Codes
DESCRIPTION
ANALOG VALUE
VCC = 5.0V
VREF = 5.0V
VCC = 2.7V
VREF = 2.5V
10
1
VREF
Least significant
bit (LSB)
VREF/4096
BINARY CODE
HEX CODE
Full-Scale
VREF – 1 LSB
1111 1111 1111
FFF
Midscale
VREF/2
1000 0000 0000
800
VREF/2 – 1 LSB
0111 1111 1111
7FF
0V
0000 0000 0000
000
Zero
100
DIGITAL OUTPUT
STRAIGHT BINARY
Full-Scale range
Midscale – 1 LSB
Supply Current (mA)
The output data from the ADS7822 is in straight
binary format, as shown in Table 2. This table
represents the ideal output code for the given input
voltage and does not include the effects of offset,
gain error, or noise.
TA = 25°C
fCLK = 1.2MHz
0.1
1
10
100
Sample Rate (kHz)
Figure 24. Maintaining fCLK at the Highest
Possible Rate Allows the Supply Current to Drop
Linearly with the Sample Rate
POWER DISSIPATION
The architecture of the converter, the semiconductor
fabrication process, and a careful design allow the
ADS7822 to convert at up to a 75kHz 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 ADS7822 scales directly
with conversion rate. So, the first step to achieving
the lowest power dissipation is to find the lowest
conversion rate that will satisfy the requirements of
the system.
In addition, the ADS7822 goes into power-down
mode under two conditions: when the conversion is
complete and whenever CS is high (see Figure 22).
Ideally, each conversion should occur as quickly as
possible; preferably, at a 1.2MHz clock rate. This
way, the converter spends the longest possible time
in the power-down mode. This is very important since
the converter not only uses power on each DCLOCK
Supply Current (mA)
1000
100
10
TA = 25°C
VCC = 2.7V
VREF = 2.5V
fCLK = 16 · fSAMPLE
1
0.1
1
10
100
Sample Rate (kHz)
Figure 25. Scaling fCLK Reduces the Supply
Current Only Slightly with the Sample Rate
Submit Documentation Feedback
Copyright © 1996–2007, Texas Instruments Incorporated
Product Folder Link(s): ADS7822
13
ADS7822
www.ti.com
SBAS062C – JANUARY 1996 – REVISED AUGUST 2007
There is an important distinction between the
power-down mode that is entered after a conversion
is complete and the full power-down mode that is
enabled when CS is high. While both shutdown the
analog section, the digital section is completely
shutdown 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; see Figure 26 for more
information.
10.0
Supply Current (mA)
8.0
TA = 25°C
VCC = 2.7V
VREF = 2.5V
fCLK = 16 · fSAMPLE
Short Cycling
Another way of saving power is to use the CS signal
to short-cycle the conversion. Because the ADS7822
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 eight bits
of the conversion result are needed, then the
conversion can be terminated (by pulling CS high)
after the eighth bit has been clocked out.
6.0
CS LOW (GND)
4.0
2.0
0.0
CS HIGH (VCC)
0.050
0.00
0.1
1
10
100
Sample Rate (kHz)
Figure 26. Shutdown Current with CS High is
Typically 50nA, Regardless of the Clock.
Shutdown Current with CS Low varies with
Sample Rate.
14
Power dissipation can also be reduced by lowering
the power-supply voltage and the reference voltage.
The ADS7822 operates over a VCC range of 2.0V to
5.25V. It will run up to a 200kHz throughput rate over
a supply range of 4.75V to 5.25V; therefore, it can be
clocked at up to 3.2MHz. However, at voltages below
2.7V, the converter does not run at a 75kHz sample
rate. See the Typical Characteristic curves for more
information regarding power-supply voltage and
maximum sample rate.
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 12-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, because they
spend more time in the power-down mode.
Submit Documentation Feedback
Copyright © 1996–2007, Texas Instruments Incorporated
Product Folder Link(s): ADS7822
ADS7822
www.ti.com
SBAS062C – JANUARY 1996 – REVISED AUGUST 2007
LAYOUT
For optimum performance, care should be taken with
the physical layout of the ADS7822 circuitry. This is
particularly true if the reference voltage is low and/or
the conversion rate is high. At a 75kHz conversion
rate, the ADS7822 makes a bit decision every 830ns.
If the supply range is limited to 4.75V to 5.25V, then
up to a 200kHz conversion rate can be used, which
reduces the bit decision time to 312ns. 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
12-bit level all within one clock cycle.
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 because the phase difference
between the two changes with time and temperature,
causing sporadic misoperation.
With this in mind, power to the ADS7822 should be
clean and well-bypassed. A 0.1μF ceramic bypass
capacitor should be placed as close to the ADS7822
package as possible. In addition, a 1μF to 10μF
capacitor and a 5Ω or 10Ω series resistor can be
used to lowpass 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 lowpass 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
ADS7822 draws very little current from the reference
on average, there are still instantaneous current
demands placed on the external reference circuitry.
Also, keep in mind that the ADS7822 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 ADS7822 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 will
include an analog ground plane for the converter and
associated analog circuitry.
APPLICATION CIRCUITS
Figure 27 and Figure 28 show some typical
application circuits for the ADS7822. Figure 27 uses
an ADS7822 and a multiplexer to provide for a
flexible data acquisition circuit. A resistor string
provides for various voltages at the multiplexer input.
The selected voltage is buffered and driven into VREF.
As shown in Figure 27, the input range of the
ADS7822 is programmable to 100mV, 200mV,
300mV, or 400mV. The 100mV range would be
useful for sensors such as the thermocouple shown.
Figure 28 shows a basic data acquisition system. The
ADS7822 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.
Submit Documentation Feedback
Copyright © 1996–2007, Texas Instruments Incorporated
Product Folder Link(s): ADS7822
15
ADS7822
www.ti.com
SBAS062C – JANUARY 1996 – REVISED AUGUST 2007
+3V
+3V
+3V
R8
26kW
D1
R1
150kW
R9
1kW
OPA237
C2
0.1mF
R3
500kW
R6
1MW
R2
59kW
TC1
0.4V
R7
5W
0.3V
U2
C1
10mF
VREF
Mux
0.2V
DCLOCK
C3
0.1mF
TC2
ADS7822
DOUT
A0
CS/SHDN
A1
Thermocouple
TC3
R4
1kW
C4
10mF
ISO Thermal Block
R10
1kW
U1
R5
500W
U3
C5
0.1mF
R11
1kW
0.1V
R12
1kW
P
3-Wire
Interface
U4
Figure 27. Thermocouple Application Using a Mux to Scale the Input Range of the ADS7822
+2.7V to +3.6V
5W
+ 1mF to
10mF
ADS7822
VREF
VCC
+In
CS
-In
DOUT
0.1mF
GND
+ 1mF to
10mF
Microcontroller
DCLOCK
Figure 28. Basic Data Acquisition System
16
Submit Documentation Feedback
Copyright © 1996–2007, Texas Instruments Incorporated
Product Folder Link(s): ADS7822
ADS7822
www.ti.com
SBAS062C – JANUARY 1996 – REVISED AUGUST 2007
Revision History
Changes from Revision B (May 2006) to Revision C ...................................................................................................... Page
•
•
•
•
•
•
•
•
•
•
Added – GND to absolute input range test conditions ..........................................................................................................
Added – GND to absolute input range test conditions ..........................................................................................................
Changed VCC min from 3.6 V to 2.7 V ...................................................................................................................................
Changed VCC max from 5.25 V to 3.6 V ................................................................................................................................
Changed VCC min from 3.6 V to 2.7 V ...................................................................................................................................
Changed VCC max from 5.25 V to 3.6 V ................................................................................................................................
Changed VCC min from 3.6 V to 2.7 V ...................................................................................................................................
Changed VCC max from 5.25 V to 3.6 V ................................................................................................................................
Added – GND to absolute input range test conditions ..........................................................................................................
Added – GND to absolute input range test conditions ..........................................................................................................
Submit Documentation Feedback
Copyright © 1996–2007, Texas Instruments Incorporated
Product Folder Link(s): ADS7822
3
3
3
3
3
3
3
3
4
4
17
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)
ADS7822E/250
ACTIVE
VSSOP
DGK
8
250
RoHS & Green
Call TI
Level-2-260C-1 YEAR
-40 to 85
A22
Samples
ADS7822E/250G4
ACTIVE
VSSOP
DGK
8
250
RoHS & Green
Call TI
Level-2-260C-1 YEAR
-40 to 85
A22
Samples
ADS7822E/2K5
ACTIVE
VSSOP
DGK
8
2500
RoHS & Green
Call TI
Level-2-260C-1 YEAR
-40 to 85
A22
Samples
ADS7822E/2K5G4
ACTIVE
VSSOP
DGK
8
2500
RoHS & Green
Call TI
Level-2-260C-1 YEAR
-40 to 85
A22
Samples
ADS7822EB/250
ACTIVE
VSSOP
DGK
8
250
RoHS & Green
Call TI
Level-2-260C-1 YEAR
-40 to 85
A22
Samples
ADS7822EB/2K5
ACTIVE
VSSOP
DGK
8
2500
RoHS & Green
Call TI
Level-2-260C-1 YEAR
-40 to 85
A22
Samples
ADS7822EB/2K5G4
ACTIVE
VSSOP
DGK
8
2500
RoHS & Green
Call TI
Level-2-260C-1 YEAR
-40 to 85
A22
Samples
ADS7822EC/250
ACTIVE
VSSOP
DGK
8
250
RoHS & Green
Call TI
Level-2-260C-1 YEAR
-40 to 85
A22
Samples
ADS7822EC/2K5
ACTIVE
VSSOP
DGK
8
2500
RoHS & Green
Call TI
Level-2-260C-1 YEAR
-40 to 85
A22
Samples
ADS7822EC/2K5G4
ACTIVE
VSSOP
DGK
8
2500
RoHS & Green
Call TI
Level-2-260C-1 YEAR
-40 to 85
A22
Samples
ADS7822U
ACTIVE
SOIC
D
8
75
RoHS & Green
NIPDAU
Level-2-260C-1 YEAR
-40 to 85
ADS
7822U
Samples
ADS7822U/2K5
ACTIVE
SOIC
D
8
2500
RoHS & Green
NIPDAU
Level-2-260C-1 YEAR
-40 to 85
ADS
7822U
Samples
ADS7822UB
ACTIVE
SOIC
D
8
75
RoHS & Green
Call TI
Level-2-260C-1 YEAR
-40 to 85
ADS
7822U
B
ADS7822UB/2K5
ACTIVE
SOIC
D
8
2500
RoHS & Green
Call TI
Level-2-260C-1 YEAR
-40 to 85
ADS
7822U
B
ADS7822UBG4
ACTIVE
SOIC
D
8
75
RoHS & Green
Call TI
Level-2-260C-1 YEAR
-40 to 85
ADS
7822U
B
ADS7822UC
ACTIVE
SOIC
D
8
75
RoHS & Green
Call TI
Level-2-260C-1 YEAR
-40 to 85
ADS
7822U
C
ADS7822UC/2K5
ACTIVE
SOIC
D
8
2500
RoHS & Green
Call TI
Level-2-260C-1 YEAR
-40 to 85
ADS
Addendum-Page 1
Samples
Samples
Samples
Samples
Samples
PACKAGE OPTION ADDENDUM
www.ti.com
Orderable Device
14-Oct-2022
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)
(4/5)
(6)
7822U
C
(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
