ADC124S021
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SNAS277F – MARCH 2005 – REVISED MARCH 2013
ADC124S021 4-Channel, 50 ksps to 200 ksps, 12-Bit A/D Converter
Check for Samples: ADC124S021
FEATURES
1
•
•
•
•
2
Specified Over a Range of Sample Rates.
Four Input Channels
Variable Power Management
Single Power Supply with 2.7V - 5.25V Range
APPLICATIONS
•
•
•
Portable Systems
Remote Data Acquisition
Instrumentation and Control Systems
KEY SPECIFICATIONS
•
•
•
•
DNL: +0.4 / −0.2 LSB (typ)
INL: ± 0.35 LSB (typ)
SNR: 72.0 dB (typ)
Power Consumption
– 3V Supply: 2.2 mW (typ)
– 5V Supply: 7.9 mW (typ)
DESCRIPTION
The ADC124S021 is a low-power, four-channel
CMOS 12-bit analog-to-digital converter with a highspeed serial interface. Unlike the conventional
practice of specifying performance at a single sample
rate only, the ADC124S021 is fully specified over a
sample rate range of 50 ksps to 200 ksps. The
converter is based on a successive-approximation
register architecture with an internal track-and-hold
circuit. It can be configured to accept up to four input
signals at inputs IN1 through IN4.
The output serial data is straight binary, and is
compatible with several standards, such as SPI™,
QSPI™, MICROWIRE, and many common DSP
serial interfaces.
The ADC124S021 operates with a single supply that
can range from +2.7V to +5.25V. Normal power
consumption using a +3V or +5V supply is 2.2 mW
and 7.9 mW, respectively. The power-down feature
reduces the power consumption to just 0.14 µW using
a +3V supply, or 0.32 µW using a +5V supply.
The ADC124S021 is packaged in a 10-lead VSSOP
package. Operation over the industrial temperature
range of −40°C to +85°C is ensured.
These devices have limited built-in ESD protection. The leads should be shorted together or the device placed in conductive foam
during storage or handling to prevent electrostatic damage to the MOS gates.
Table 1. Pin-Compatible Alternatives by Resolution and Speed (1)
Resolution
(1)
Specified for Sample Rate Range of:
50 to 200 ksps
200 to 500 ksps
500 ksps to 1 Msps
12-bit
ADC124S021
ADC124S051
ADC124S101
10-bit
ADC104S021
ADC104S051
ADC104S101
8-bit
ADC084S021
ADC084S051
ADC084S101
All devices are fully pin and function compatible.
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 © 2005–2013, Texas Instruments Incorporated
ADC124S021
SNAS277F – MARCH 2005 – REVISED MARCH 2013
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Connection Diagram
CS
1
10
VA
2
9
DOUT
GND
3
8
DIN
ADC124S021
SCLK
IN4
4
7
IN1
IN3
5
6
IN2
Figure 1. 10-Lead VSSOP
See DGK Package
Block Diagram
IN1
.
.
.
MUX
IN4
T/H
12-Bit
SUCCESSIVE
APPROXIMATION
ADC
VA
CONTROL
LOGIC
CS
GND
GND
SCLK
DIN
DOUT
PIN DESCRIPTIONS AND EQUIVALENT CIRCUITS
Pin No.
Symbol
Description
ANALOG I/O
4-7
IN1 to IN4
Analog inputs. These signals can range from 0V to VA.
DIGITAL I/O
10
SCLK
Digital clock input. This clock directly controls the conversion and readout processes.
9
DOUT
Digital data output. The output samples are clocked out of this pin on falling edges of the
SCLK pin.
8
DIN
Digital data input. The ADC124S021's Control Register is loaded through this pin on rising
edges of the SCLK pin.
1
CS
Chip select. On the falling edge of CS, a conversion process begins. Conversions continue
as long as CS is held low.
2
VA
Positive supply pin. This pin should be connected to a quiet +2.7V to +5.25V source and
bypassed to GND with a 1 µF capacitor and a 0.1 µF monolithic capacitor located within 1
cm of the power pin.
3
GND
POWER SUPPLY
2
The ground return for the supply and signals.
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Absolute Maximum Ratings
(1) (2) (3)
−0.3V to 6.5V
Supply Voltage VA
Voltage on Any Pin to GND
−0.3V to VA +0.3V
(4)
±10 mA
Input Current at Any Pin
Package Input Current (4)
±20 mA
Power Consumption at TA = 25°C
See
(5)
(6)
ESD Susceptibility
Human Body Model
Machine Model
2500V
250V
Junction Temperature
+150°C
Storage Temperature
−65°C to +150°C
(1)
(2)
(3)
(4)
(5)
(6)
Absolute Maximum Ratings indicate limits beyond which damage to the device may occur. Operating Ratings indicate conditions for
which the device is functional, but do not ensure specific performance limits. For ensured specifications and test conditions, see the
Electrical Characteristics. The ensured specifications apply only for the test conditions listed. Some performance characteristics may
degrade when the device is not operated under the listed test conditions.
All voltages are measured with respect to GND = 0V, unless otherwise specified.
If Military/Aerospace specified devices are required, please contact the Texas Instruments Sales Office/ Distributors for availability and
specifications.
When the input voltage at any pin exceeds the power supply (that is, VIN < GND or VIN > VA), the current at that pin should be limited to
10 mA. The 20 mA maximum package input current rating limits the number of pins that can safely exceed the power supplies with an
input current of 10 mA to two. The Absolute Maximum Rating specification does not apply to the VA pin. The current into the VA pin is
limited by the Analog Supply Voltage specification.
The absolute maximum junction temperature (TJmax) for this device is 150°C. The maximum allowable power dissipation is dictated by
TJmax, the junction-to-ambient thermal resistance (θJA), and the ambient temperature (TA), and can be calculated using the formula
PDMAX = (TJmax − TA)/θJA. The values for maximum power dissipation listed above will be reached only when the device is operated in
a severe fault condition (e.g. when input or output pins are driven beyond the power supply voltages, or the power supply polarity is
reversed). Obviously, such conditions should always be avoided.
Human body model is 100 pF capacitor discharged through a 1.5 kΩ resistor. Machine model is 220 pF discharged through zero ohms.
Operating Ratings
(1) (2)
−40°C ≤ TA ≤ +85°C
Operating Temperature Range
VA Supply Voltage
+2.7V to +5.25V
−0.3V to VA
Digital Input Pins Voltage Range
Clock Frequency
50 kHz to 16 MHz
Analog Input Voltage
(1)
(2)
0V to VA
Absolute Maximum Ratings indicate limits beyond which damage to the device may occur. Operating Ratings indicate conditions for
which the device is functional, but do not ensure specific performance limits. For ensured specifications and test conditions, see the
Electrical Characteristics. The ensured specifications apply only for the test conditions listed. Some performance characteristics may
degrade when the device is not operated under the listed test conditions.
All voltages are measured with respect to GND = 0V, unless otherwise specified.
Package Thermal Resistance
Package
θJA
10-lead VSSOP
190°C / W
Soldering process must comply with Reflow Temperature Profile specifications. Refer to http://www.ti.com/packaging. (1)
(1)
Reflow temperature profiles are different for lead-free and non-lead-free packages.
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ADC124S021 Converter Electrical Characteristics
(1)
The following specifications apply for VA = +2.7V to 5.25V, GND = 0V, fSCLK = 0.8 MHz to 3.2 MHz, fSAMPLE = 50 ksps to 200
ksps, CL = 35 pF, unless otherwise noted. Boldface limits apply for TA = TMIN to TMAX: all other limits TA = 25°C.
Symbol
Parameter
Conditions
Typical
Limits
(2)
Units
STATIC CONVERTER CHARACTERISTICS
Resolution with No Missing Codes
INL
Integral Non-Linearity
12
Bits
+0.35
+0.8
LSB (max)
−0.35
−1.1
LSB (min)
+0.4
+1.1
LSB (max)
DNL
Differential Non-Linearity
−0.2
−0.8
LSB (min)
VOFF
Offset Error
+0.37
±1.3
LSB (max)
OEM
Channel to Channel Offset Error Match
±0.1
±1.0
LSB (max)
FSE
Full-Scale Error
±0.52
±1.5
LSB (max)
FSEM
Channel to Channel Full-Scale Error
Match
±0.1
±1.0
LSB (max)
DYNAMIC CONVERTER CHARACTERISTICS
SINAD
Signal-to-Noise Plus Distortion Ratio
VA = +2.7 to 5.25V
fIN = 39.9 kHz, −0.02 dBFS
72
69.2
dB (min)
SNR
Signal-to-Noise Ratio
VA = +2.7 to 5.25V
fIN = 39.9 kHz, −0.02 dBFS
72
70.6
dB (min)
THD
Total Harmonic Distortion
VA = +2.7 to 5.25V
fIN = 39.9 kHz, −0.02 dBFS
−84
−75
dB (max)
SFDR
Spurious-Free Dynamic Range
VA = +2.7 to 5.25V
fIN = 39.9 kHz, −0.02 dBFS
86
76
dB (min)
ENOB
Effective Number of Bits
VA = +2.7 to 5.25V
11.7
11.2
Bits (min)
Channel-to-Channel Crosstalk
VA = +5.25V
fIN = 39.9 kHz
−86
dB
Intermodulation Distortion, Second
Order Terms
VA = +5.25V
fa = 40.161 kHz, fb = 41.015 kHz
−87
dB
Intermodulation Distortion, Third Order
Terms
VA = +5.25V
fa = 40.161 kHz, fb = 41.015 kHz
−88
dB
VA = +5V
11
MHz
VA = +3V
8
MHz
IMD
FPBW
-3 dB Full Power Bandwidth
ANALOG INPUT CHARACTERISTICS
VIN
Input Range
IDCL
DC Leakage Current
CINA
Input Capacitance
0 to VA
±0.02
V
±1
µA (max)
Track Mode
33
pF
Hold Mode
3
pF
DIGITAL INPUT CHARACTERISTICS
VIH
Input High Voltage
VIL
Input Low Voltage
IIN
Input Current
CIND
Digital Input Capacitance
VA = +5.25V
2.4
VA = +3.6V
2.1
V (min)
0.8
V (max)
±0.02
±10
µA (max)
2
4
pF (max)
ISOURCE = 200 µA
VA − 0.03
VA − 0.5
V (min)
ISOURCE = 1 mA
VA − 0.1
ISINK = 200 µA
0.02
ISINK = 1 mA
0.1
VIN = 0V or VA
V (min)
DIGITAL OUTPUT CHARACTERISTICS
VOH
Output High Voltage
VOL
Output Low Voltage
IOZH, IOZL TRI-STATE® Leakage Current
(1)
(2)
4
±0.01
V
0.4
V (max)
±1
µA (max)
V
Min/max specification limits are ensured by design, test, or statistical analysis.
Tested limits are specified to TI's AOQL (Average Outgoing Quality Level).
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ADC124S021 Converter Electrical Characteristics (1) (continued)
The following specifications apply for VA = +2.7V to 5.25V, GND = 0V, fSCLK = 0.8 MHz to 3.2 MHz, fSAMPLE = 50 ksps to 200
ksps, CL = 35 pF, unless otherwise noted. Boldface limits apply for TA = TMIN to TMAX: all other limits TA = 25°C.
Symbol
COUT
Parameter
Conditions
Typical
TRI-STATE® Output Capacitance
Limits
2
Output Coding
(2)
Units
4
pF (max)
Straight (Natural) Binary
POWER SUPPLY CHARACTERISTICS (CL = 10 pF)
VA
Supply Voltage
Supply Current, Normal Mode
(Operational, CS low)
IA
2.7
V (min)
5.25
V (max)
VA = +5.25V
fSAMPLE = 200 ksps, fIN = 39.9 kHz
1.5
2.1
mA (max)
VA = +3.6V,
fSAMPLE = 200 ksps, fIN = 39.9 kHz
0.62
1.0
mA (max)
VA = +5.25V
fSAMPLE = 0 ksps
60
nA
VA = +3.6V,
fSAMPLE = 0 ksps
38
nA
Power Consumption, Normal Mode
(Operational, CS low)
VA = +5.25V
7.9
11.0
mW (max)
VA = +3.6V,
2.2
3.6
mW (max)
Power Consumption, Shutdown (CS
high)
VA = +5.25V
0.32
µW
VA = +3.6V,
0.14
µW
Supply Current, Shutdown (CS high)
PD
AC ELECTRICAL CHARACTERISTICS
fSCLK
(3)
Maximum Clock Frequency
fS
Sample Rate
tCONV
Conversion Time
0.8
MHz (min)
3.2
MHz (max)
50
ksps (min)
200
ksps (max)
13
SCLK cycles
(3)
% (min)
70
% (max)
DC
SCLK Duty Cycle
fSCLK = 3.2 MHz
tACQ
Track/Hold Acquisition Time
Full-Scale Step Input
3
SCLK cycles
Throughput Time
Acquisition Time + Conversion Time
16
SCLK cycles
(3)
50
30
This is the frequency range over which the electrical performance is ensured. The device is functional over a wider range which is
specified under Operating Ratings.
ADC124S021 Timing Specifications
The following specifications apply for VA = +2.7V to 5.25V, GND = 0V, fSCLK = 0.8 MHz to 3.2 MHz, fSAMPLE = 50 ksps to 200
ksps, CL = 35 pF, Boldface limits apply for TA = TMIN to TMAX: all other limits TA = 25°C.
Symbol
(1)
(2)
Parameter
Conditions
tCSU
Setup Time SCLK High to CS Falling Edge
(2)
tCLH
Hold time SCLK Low to CS Falling Edge
(2)
tEN
Delay from CS Until DOUT active
tACC
Data Access Time after SCLK Falling Edge
tSU
Data Setup Time Prior to SCLK Rising Edge
tH
Data Valid SCLK Hold Time
tCH
SCLK High Pulse Width
Typical
VA = +3.0V
−3.5
VA = +5.0V
−0.5
VA = +3.0V
+4.5
VA = +5.0V
+1.5
VA = +3.0V
+4
VA = +5.0V
+2
VA = +3.0V
+14.5
VA = +5.0V
+13
Limits
(1)
Units
10
ns (min)
10
ns (min)
30
ns (max)
30
ns (max)
+3
10
ns (min)
+3
10
ns (min)
0.5 x tSCLK 0.3 x tSCLK
ns (min)
Tested limits are specified to TI's AOQL (Average Outgoing Quality Level).
Clock may be either high or low when CS is asserted as long as setup and hold times tCSU and tCLH are strictly observed.
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ADC124S021 Timing Specifications (continued)
The following specifications apply for VA = +2.7V to 5.25V, GND = 0V, fSCLK = 0.8 MHz to 3.2 MHz, fSAMPLE = 50 ksps to 200
ksps, CL = 35 pF, Boldface limits apply for TA = TMIN to TMAX: all other limits TA = 25°C.
Symbol
tCL
Parameter
Conditions
SCLK Low Pulse Width
Limits
(1)
Units
0.5 x tSCLK 0.3 x tSCLK
Output Falling
tDIS
Typical
CS Rising Edge to DOUT High-Impedance
Output Rising
VA = +3.0V
1.8
VA = +5.0V
1.3
VA = +3.0V
1.0
VA = +5.0V
1.0
20
ns (min)
ns (max)
Timing Diagrams
Power Down
Power Up
Track
Power Up
Hold
Track
Hold
CS
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
1
2
3
4
5
6
7
9
8
10
SCLK
Control register
Control register
DIN
DOUT
b7
b6
b5
b4
b3
b2
b1
DB11 DB10 DB9
b0
b7
DB8
DB7
DB6
DB5
DB4
DB3
DB2
DB1
b6
b5
DB0
b4
b3
b2
b1
DB11 DB10 DB9
b0
DB8
DB7
Figure 2. ADC124S021 Operational Timing Diagram
IOL
200 PA
To Output Pin
1.6V
CL
35 pF
IOH
200 PA
Figure 3. Timing Test Circuit
6
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CS
tACQ
tCONVERT
tCH
SCLK
1
2
3
4
6
DOUT
Z3
tSU
Z2
Z1
7
8
16
tACC
tCL
tEN
DIN
5
Z0
DB11
DB10
tDIS
DB9
DB1
DB8
DB0
tH
DONT DONTC ADD2
ADD1
ADD0
DONTC DONTC DONTC
Figure 4. ADC124S021 Serial Timing Diagram
CS
tCSU
SCLK
tCLH
SCLK
Figure 5. SCLK and CS Timing Parameters
Specification Definitions
ACQUISITION TIME is the time required to acquire the input voltage. That is, it is time required for the hold
capacitor to charge up to the input voltage.
APERTURE DELAY is the time between the fourth falling SCLK edge of a conversion and the time when the
input signal is acquired or held for conversion.
CONVERSION TIME is the time required, after the input voltage is acquired, for the ADC to convert the input
voltage to a digital word.
CROSSTALK is the coupling of energy from one channel into the other channel, or the amount of signal energy
from one analog input that appears at the measured analog input.
DIFFERENTIAL NON-LINEARITY (DNL) is the measure of the maximum deviation from the ideal step size of 1
LSB.
DUTY CYCLE is the ratio of the time that a repetitive digital waveform is high to the total time of one period. The
specification here refers to the SCLK
EFFECTIVE NUMBER OF BITS (ENOB, or EFFECTIVE BITS) is another method of specifying Signal-to-Noise
and Distortion or SINAD. ENOB is defined as (SINAD − 1.76) / 6.02 and says that the converter is
equivalent to a perfect ADC of this (ENOB) number of bits.
FULL POWER BANDWIDTH is a measure of the frequency at which the reconstructed output fundamental
drops 3 dB below its low frequency value for a full scale input.
FULL SCALE ERROR (FSE) is a measure of how far the last code transition is from the ideal 1½ LSB below
VREF+ and is defined as:
VFSE = Vmax + 1.5 LSB – VREF+
where
•
•
Vmax is the voltage at which the transition to the maximum code occurs
FSE can be expressed in Volts, LSB or percent of full scale range
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GAIN ERROR is the deviation of the last code transition (111...110) to (111...111) from the ideal (VREF − 1.5
LSB), after adjusting for offset error.
INTEGRAL NON-LINEARITY (INL) is a measure of the deviation of each individual code from a line drawn from
negative full scale (½ LSB below the first code transition) through positive full scale (½ LSB above the last
code transition). The deviation of any given code from this straight line is measured from the center of that
code value.
INTERMODULATION DISTORTION (IMD) is the creation of additional spectral components as a result of two
sinusoidal frequencies being applied to the ADC input at the same time. It is defined as the ratio of the
power in the second and third order intermodulation products to the power in one of the original
frequencies. IMD is usually expressed in dB.
MISSING CODES are those output codes that will never appear at the ADC outputs. These codes cannot be
reached with any input value. The ADC124S021 is ensured not to have any missing codes.
OFFSET ERROR is the deviation of the first code transition (000...000) to (000...001) from the ideal (i.e. GND +
0.5 LSB).
SIGNAL TO NOISE RATIO (SNR) is the ratio, expressed in dB, of the rms value of the input signal to the rms
value of the sum of all other spectral components below one-half the sampling frequency, not including
d.c. or the harmonics included in THD.
SIGNAL TO NOISE PLUS DISTORTION (S/N+D or SINAD) Is the ratio, expressed in dB, of the rms value of
the input signal to the rms value of all of the other spectral components below half the clock frequency,
including harmonics but excluding d.c.
SPURIOUS FREE DYNAMIC RANGE (SFDR) is the difference, expressed in dB, between the desired signal
amplitude to the amplitude of the peak spurious spectral component, where a spurious spectral
component is any signal present in the output spectrum that is not present at the input and may or may
not be a harmonic.
TOTAL HARMONIC DISTORTION (THD) is the ratio, expressed in dB or dBc, of the rms total of the first five
harmonic components at the output to the rms level of the input signal frequency as seen at the output.
THD is calculated as
THD = 20 ‡ log10
A f 22 +
+ A f 62
A f12
where
•
•
Af1 is the RMS power of the input frequency at the output
Af2 through Af6 are the RMS power in the first 5 harmonic frequencies
(2)
THROUGHPUT TIME is the minimum time required between the start of two successive conversion. It is the
acquisition time plus the conversion and read out times. In the case of the ADC124S021, this is 16 SCLK
periods.
8
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Typical Performance Characteristics
TA = +25°C, fSAMPLE = 50 ksps to 200 ksps, fSCLK = 0.8 MHz to 3.2 MHz, fIN = 39.9 kHz unless otherwise stated.
DNL - VA = 3.0V
INL - VA = 3.0V
Figure 6.
Figure 7.
DNL - VA = 5.0V
INL - VA = 5.0V
Figure 8.
Figure 9.
DNL
vs.
Supply
INL
vs.
Supply
Figure 10.
Figure 11.
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Typical Performance Characteristics (continued)
TA = +25°C, fSAMPLE = 50 ksps to 200 ksps, fSCLK = 0.8 MHz to 3.2 MHz, fIN = 39.9 kHz unless otherwise stated.
10
DNL
vs.
Clock Frequency
INL
vs.
Clock Frequency
Figure 12.
Figure 13.
DNL
vs.
Clock Duty Cycle
INL
vs.
Clock Duty Cycle
Figure 14.
Figure 15.
DNL
vs.
Temperature
INL
vs.
Temperature
Figure 16.
Figure 17.
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Typical Performance Characteristics (continued)
TA = +25°C, fSAMPLE = 50 ksps to 200 ksps, fSCLK = 0.8 MHz to 3.2 MHz, fIN = 39.9 kHz unless otherwise stated.
SNR
vs.
Supply
THD
vs.
Supply
Figure 18.
Figure 19.
SNR
vs.
Clock Frequency
THD
vs.
Clock Frequency
Figure 20.
Figure 21.
SNR
vs.
Clock Duty Cycle
THD
vs.
Clock Duty Cycle
Figure 22.
Figure 23.
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Typical Performance Characteristics (continued)
TA = +25°C, fSAMPLE = 50 ksps to 200 ksps, fSCLK = 0.8 MHz to 3.2 MHz, fIN = 39.9 kHz unless otherwise stated.
12
SNR
vs.
Input Frequency
THD
vs.
Input Frequency
Figure 24.
Figure 25.
SNR
vs.
Temperature
THD
vs.
Temperature
Figure 26.
Figure 27.
SFDR
vs.
Supply
SINAD
vs.
Supply
Figure 28.
Figure 29.
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Typical Performance Characteristics (continued)
TA = +25°C, fSAMPLE = 50 ksps to 200 ksps, fSCLK = 0.8 MHz to 3.2 MHz, fIN = 39.9 kHz unless otherwise stated.
SFDR
vs.
Clock Frequency
SINAD
vs.
Clock Frequency
Figure 30.
Figure 31.
SFDR
vs.
Clock Duty Cycle
SINAD
vs.
Clock Duty Cycle
Figure 32.
Figure 33.
SFDR
vs.
Input Frequency
SINAD
vs.
Input Frequency
Figure 34.
Figure 35.
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Typical Performance Characteristics (continued)
TA = +25°C, fSAMPLE = 50 ksps to 200 ksps, fSCLK = 0.8 MHz to 3.2 MHz, fIN = 39.9 kHz unless otherwise stated.
14
SFDR
vs.
Temperature
SINAD
vs.
Temperature
Figure 36.
Figure 37.
ENOB
vs.
Supply
ENOB
vs.
Clock Frequency
Figure 38.
Figure 39.
ENOB
vs.
Clock Duty Cycle
ENOB
vs.
Input Frequency
Figure 40.
Figure 41.
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Typical Performance Characteristics (continued)
TA = +25°C, fSAMPLE = 50 ksps to 200 ksps, fSCLK = 0.8 MHz to 3.2 MHz, fIN = 39.9 kHz unless otherwise stated.
ENOB
vs.
Temperature
Spectral Response - 3V, 200 ksps
Figure 42.
Figure 43.
Spectral Response - 5V, 200 ksps
Power Consumption
vs.
Throughput
Figure 44.
Figure 45.
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APPLICATIONS INFORMATION
1.0 ADC124S021 OPERATION
The ADC124S021 is a successive-approximation analog-to-digital converter designed around a chargeredistribution digital-to-analog converter. Simplified schematics of the ADC124S021 in both track and hold modes
are shown in Figure 46, and Figure 47, respectively. In Figure 46, the ADC124S021 is in track mode: switch
SW1 connects the sampling capacitor to one of four analog input channels through the multiplexer, and SW2
balances the comparator inputs. The ADC124S021 is in this state for the first three SCLK cycles after CS is
brought low.
Figure 47 shows the ADC124S021 in hold mode: switch SW1 connects the sampling capacitor to ground,
maintaining the sampled voltage, and switch SW2 unbalances the comparator. The control logic then instructs
the charge-redistribution DAC to add fixed amounts of charge to the sampling capacitor until the comparator is
balanced. When the comparator is balanced, the digital word supplied to the DAC is the digital representation of
the analog input voltage. The ADC124S021 is in this state for the fourth through sixteenth SCLK cycles after CS
is brought low.
The time when CS is low is considered a serial frame. Each of these frames should contain an integer multiple of
16 SCLK cycles, during which time a conversion is performed and clocked out at the DOUT pin and data is
clocked into the DIN pin to indicate the multiplexer address for the next conversion.
CHARGE
REDISTRIBUTION
DAC
IN1
MUX
SAMPLING
CAPACITOR
IN4
SW1
SW2
AGND
+
-
CONTROL
LOGIC
VA
2
Figure 46. ADC124S021 in Track Mode
CHARGE
REDISTRIBUTION
DAC
IN1
MUX
SAMPLING
CAPACITOR
IN4
SW1
SW2
AGND
+
-
CONTROL
LOGIC
VA
2
Figure 47. ADC124S021 in Hold Mode
2.0 USING THE ADC124S021
Figure 2 and Figure 4 for the ADC124S021 are shown in Timing Diagrams. CS is chip select, which initiates
conversions and frames the serial data transfers. SCLK (serial clock) controls both the conversion process and
the timing of serial data. DOUT is the serial data output pin, where a conversion result is sent as a serial data
stream, MSB first. Data to be written to the ADC124S021's Control Register is placed on DIN, the serial data
input pin. New data is written to the ADC at DIN with each conversion.
A serial frame is initiated on the falling edge of CS and ends on the rising edge of CS. Each frame must contain
an integer multiple of 16 rising SCLK edges. The ADC output data (DOUT) is in a high impedance state when
CS is high and is active when CS is low. Thus, CS acts as an output enable. Additionally, the device goes into a
power down state when CS is high, and also between continuous conversion cycles.
16
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During the first 3 cycles of SCLK, the ADC is in the track mode, acquiring the input voltage. For the next 13
SCLK cycles the conversion is accomplished and the data is clocked out, MSB first, starting on the 5th clock. If
there is more than one conversion in a frame, the ADC will re-enter the track mode on the falling edge of SCLK
after the N*16th rising edge of SCLK, and re-enter the hold/convert mode on the N*16+4th falling edge of SCLK,
where "N" is an integer.
When CS is brought high, SCLK is internally gated off. If SCLK is stopped in the low state while CS is high, the
subsequent fall of CS will generate a falling edge of the internal version of SCLK, putting the ADC into the track
mode. This is seen by the ADC as the first falling edge of SCLK. If SCLK is stopped with SCLK high, the ADC
enters the track mode on the first falling edge of SCLK after the falling edge of CS.
During each conversion, data is clocked into the DIN pin on the first 8 rising edges of SCLK after the fall of CS.
For each conversion, it is necessary to clock in the data indicating the input that is selected for the conversion
after the current one. See Table 2, Table 3, and Table 4.
If CS and SCLK go low within the times defined by tCSU and tCLH, the rising edge of SCLK that begins clocking
data in at DIN may be one clock cycle later than expected. It is, therefore, best to strictly observe the minimum
tCSU and tCLH times given in ADC124S021 Timing Specifications .
There are no power-up delays or dummy conversions required with the ADC124S021. The ADC is able to
sample and convert an input to full conversion immediately following power up. The first conversion result after
power-up will be that of IN1.
Table 2. Control Register Bits
Bit 7 (MSB)
Bit 6
Bit 5
Bit 4
Bit 3
Bit 2
Bit 1
Bit 0
DONTC
DONTC
ADD2
ADD1
ADD0
DONTC
DONTC
DONTC
Table 3. Control Register Bit Descriptions
Bit #:
Symbol:
Description
7 - 6, 2 - 0
DONTC
Don't care. The value of these bits do not affect device operation.
5
ADD2
4
ADD1
3
ADD0
These three bits determine which input channel will be sampled and converted in the next
track/hold cycle. The mapping between codes and channels is shown in Table 4.
Table 4. Input Channel Selection
ADD2
ADD1
ADD0
Input Channel
x
0
0
IN1 (Default)
x
0
1
IN2
x
1
0
IN3
x
1
1
IN4
3.0 ADC124S021 TRANSFER FUNCTION
The output format of the ADC124S021 is straight binary. Code transitions occur midway between successive
integer LSB values. The LSB width for the ADC124S021 is VA/4096. The ideal transfer characteristic is shown in
Figure 3. The transition from an output code of 0000 0000 0000 to a code of 0000 0000 0001 is at 1/2 LSB, or a
voltage of VA/8192. Other code transitions occur at steps of one LSB.
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111...111
111...000
|
|
ADC CODE
111...110
1LSB = VA/4096
011...111
000...010
|
000...001
000...000
0.5LSB
0V
ANALOG INPUT
+VA - 1.5LSB
Figure 48. Ideal Transfer Characteristic
4.0 TYPICAL APPLICATION CIRCUIT
A typical application of the ADC124S021 is shown in Figure 49. Power is provided in this example by the Texas
Instruments LP2950 low-dropout voltage regulator, available in a variety of fixed and adjustable output voltages.
The power supply pin is bypassed with a capacitor network located close to the ADC124S021.
Because the reference for the ADC124S021 is the supply voltage, any noise on the supply will degrade device
noise performance. To keep noise off the supply, use a dedicated linear regulator for this device, or provide
sufficient decoupling from other circuitry to keep noise off the ADC124S021 supply pin. Because of the
ADC124S021's low power requirements, it is also possible to use a precision reference as a power supply to
maximize performance. The four-wire interface is also shown connected to a microprocessor or DSP.
LP2950
1 PF
TANT
VA
IN1
IN2
IN3
1 PF
0.1 PF
SCLK
ADC124S021
IN4
0.1 PF
5V
CS
DIN
MICROPROCESSOR
DSP
DOUT
GND
Figure 49. Typical Application Circuit
5.0 ANALOG INPUTS
An equivalent circuit for one of the ADC124S021's input channels is shown in Figure 5. Diodes D1 and D2
provide ESD protection for the analog inputs. At no time should any input go beyond (VA + 300 mV) or (GND −
300 mV), as these ESD diodes will begin conducting, which could result in erratic operation. For this reason,
these ESD diodes should NOT be used to clamp the input signal.
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The capacitor C1 in Figure 5 has a typical value of 3 pF, and is mainly the package pin capacitance. Resistor R1
is the on resistance of the multiplexer and track / hold switch, and is typically 500 ohms. Capacitor C2 is the
ADC124S021 sampling capacitor, and is typically 30 pF. The ADC124S021 will deliver best performance when
driven by a low-impedance source to eliminate distortion caused by the charging of the sampling capacitance.
This is especially important when using the ADC124S021 to sample AC signals. Also important when sampling
dynamic signals is a band-pass or low-pass filter to reduce harmonics and noise, improving dynamic
performance.
VA
D1
R1
C2
30 pF
VIN
C1
3 pF
D2
Conversion Phase - Switch Open
Track Phase - Switch Closed
Figure 50. Equivalent Input Circuit
6.0 DIGITAL INPUTS AND OUTPUTS
The ADC124S021's digital output DOUT is limited by, and cannot exceed, the supply voltage, VA. The digital
input pins are not prone to latch-up and, and although not recommended, SCLK, CS and DIN may be asserted
before VA without any latch-up risk.
7.0 POWER SUPPLY CONSIDERATIONS
The ADC124S021 is fully powered-up whenever CS is low, and fully powered-down whenever CS is high, with
one exception: the ADC124S021 automatically enters power-down mode between the 16th falling edge of a
conversion and the 1st falling edge of the subsequent conversion (see Timing Diagramss).
The ADC124S021 can perform multiple conversions back to back; each conversion requires 16 SCLK cycles.
The ADC124S021 will perform conversions continuously as long as CS is held low.
The user may trade off throughput for power consumption by simply performing fewer conversions per unit time.
Figure 45 in Typical Performance Characteristics shows the typical power consumption of the ADC124S021
versus throughput. To calculate the power consumption, simply multiply the fraction of time spent in the normal
mode by the normal mode power consumption , and add the fraction of time spent in shutdown mode multiplied
by the shutdown mode power dissipation.
7.1 Power Management
When the ADC124S021 is operated continuously in normal mode, the maximum throughput is fSCLK/16.
Throughput may be traded for power consumption by running fSCLK at its maximum 3.2 MHz and performing
fewer conversions per unit time, putting the ADC124S021 into shutdown mode between conversions. Figure 45
is shown in Typical Performance Characteristics. To calculate the power consumption for a given throughput,
multiply the fraction of time spent in the normal mode by the normal mode power consumption and add the
fraction of time spent in shutdown mode multiplied by the shutdown mode power consumption. Generally, the
user will put the part into normal mode and then put the part back into shutdown mode. Note that Figure 45 is
nearly linear. This is because the power consumption in the shutdown mode is so small that it can be ignored for
all practical purposes.
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7.2 Power Supply Noise Considerations
The charging of any output load capacitance requires current from the power supply, VA. The current pulses
required from the supply to charge the output capacitance will cause voltage variations on the supply. If these
variations are large enough, they could degrade SNR and SINAD performance of the ADC. Furthermore,
discharging the output capacitance when the digital output goes from a logic high to a logic low will dump current
into the die substrate, which is resistive. Load discharge currents will cause "ground bounce" noise in the
substrate that will degrade noise performance if that current is large enough. The larger is the output
capacitance, the more current flows through the die substrate and the greater is the noise coupled into the
analog channel, degrading noise performance.
To keep noise out of the power supply, keep the output load capacitance as small as practical. If the load
capacitance is greater than 35 pF, use a 100 Ω series resistor at the ADC output, located as close to the ADC
output pin as practical. This will limit the charge and discharge current of the output capacitance and improve
noise performance.
20
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REVISION HISTORY
Changes from Revision E (March 2013) to Revision F
•
Page
Changed layout of National Data Sheet to TI format .......................................................................................................... 20
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PACKAGE OPTION ADDENDUM
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10-Dec-2020
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)
(4/5)
(6)
ADC124S021CIMM/NOPB
ACTIVE
VSSOP
DGS
10
1000
RoHS & Green
SN
Level-1-260C-UNLIM
-40 to 85
X21C
ADC124S021CIMMX/NOPB
ACTIVE
VSSOP
DGS
10
3500
RoHS & Green
SN
Level-1-260C-UNLIM
-40 to 85
X21C
(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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