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An IMPORTANT NOTICE at the end of this data sheet addresses availability, warranty, changes, use in safety-critical applications,
intellectual property matters and other important disclaimers. PRODUCTION DATA.
ADC121S021
SNAS305J JULY 2005REVISED MARCH 2016
ADC121S021 Single-Channel, 50- to 200-ksps, 12-Bit A/D Converter
1
1 Features
1 Specified Over a Range of Sample Rates
Variable Power Management
Single Power Supply With 2.7-V to 5.25-V Range
Compatible With the SPI, QSPI, MICROWIRE,
and DSP
Key Specifications:
DNL: 0.45 and –0.25 LSB (Typical)
INL: 0.45 and –0.4 LSB (Typical)
SNR: 72.3 dB (Typical)
Power Consumption
3.6-V Supply: 1.5 mW (Typical)
5.25-V Supply: 7.9 mW (Typical)
2 Applications
Portable Systems
Remote Data Acquisition
Instrumentation and Control Systems
3 Description
The ADC121S021 device is a low-power, single-
channel CMOS 12-bit analog-to-digital converter with
a high-speed serial interface. Unlike the conventional
practice of specifying performance at a single sample
rate only, the ADC121S021 is fully specified over a
sample rate range of 50 ksps to 200 ksps. The
converter is based upon a successive-approximation
register architecture with an internal track-and-hold
circuit.
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 ADC121S021 operates with a single supply that
can range from 2.7 V to 5.25 V. Normal power
consumption using a 3.6-V or 5.25-V supply is 1.5
mW and 7.9 mW, respectively. The power-down
feature reduces the power consumption to as low as
2.6 µW using a 5.25-V supply.
The ADC121S021 is packaged in 6-pin WSON and
SOT-23 packages. Operation over the industrial
temperature range of –40°C to 85°C is ensured.
Device Information(1)
PART NUMBER PACKAGE BODY SIZE (NOM)
ADC121S021 SOT-23 (6) 2.90 mm × 1.60 mm
WSON (6) 2.50 mm × 2.20 mm
(1) For all available packages, see the orderable addendum at
the end of the data sheet.
Key Graphic
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Table of Contents
1 Features.................................................................. 1
2 Applications ........................................................... 1
3 Description............................................................. 1
4 Revision History..................................................... 2
5 Device Comparison Table..................................... 3
6 Pin Configuration and Functions......................... 3
7 Specifications......................................................... 4
7.1 Absolute Maximum Ratings ...................................... 4
7.2 ESD Ratings.............................................................. 4
7.3 Recommended Operating Conditions....................... 4
7.4 Thermal Information.................................................. 5
7.5 Electrical Characteristics........................................... 5
7.6 Timing Requirements................................................ 7
7.7 Typical Characteristics.............................................. 8
8 Parameter Measurement Information .................. 9
9 Detailed Description............................................ 10
9.1 Overview................................................................. 10
9.2 Functional Block Diagram....................................... 10
9.3 Feature Description................................................. 10
9.4 Device Functional Modes........................................ 10
10 Applications Information.................................... 12
10.1 Application Information.......................................... 12
10.2 Typical Application................................................ 15
11 Power Supply Recommendations ..................... 17
11.1 Power Supply Noise Considerations..................... 17
12 Layout................................................................... 17
12.1 Layout Guidelines ................................................. 17
12.2 Layout Example .................................................... 17
13 Device and Documentation Support................. 18
13.1 Device Support...................................................... 18
13.2 Community Resources.......................................... 19
13.3 Trademarks........................................................... 19
13.4 Electrostatic Discharge Caution............................ 19
13.5 Glossary................................................................ 19
14 Mechanical, Packaging, and Orderable
Information........................................................... 19
4 Revision History
NOTE: Page numbers for previous revisions may differ from page numbers in the current version.
Changes from Revision I (January 2014) to Revision J Page
Added ESD Ratings table,Feature Descriptionsection, Device Functional Modes,Application and Implementation
section, Power Supply Recommendationssection, Layoutsection, Device and Documentation Support section,
andMechanical, Packaging, and Orderable Information section............................................................................................ 1
Changes from Revision H (March 2013) to Revision I Page
Changed sentence in the "Using the ADC121S021" section............................................................................................... 13
Changes from Revision G (March 2013) to Revision H Page
Changed layout of National Data Sheet to TI format ........................................................................................................... 17
PAD
1VA!CS
2GND 5 SDATA
3VIN! 4 SCLK
6
1VA!CS
2GND 5 SDATA
3VIN! 4 SCLK
6
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(1) All devices are fully pin and function compatible.
5 Device Comparison Table(1)
RESOLUTION SPECIFIED FOR SAMPLE RATE RANGE OF:
50 to 200 ksps 200 to 500 ksps 500 ksps to 1 Msps
12-bit ADC121S021 ADC121S051 ADC121S101
10-bit ADC101S021 ADC101S051 ADC101S101
8-bit ADC081S021 ADC081S051 ADC081S101
6 Pin Configuration and Functions
DBV Package
6-Pin SOT-23
Top View
See package number DBV0006A.
NGF Package
6-Pin WSON
Top View
See package number NGF0006A.
Pin Functions
PIN TYPE DESCRIPTION
NAME NO.
CS 6 Digital I/O Chip select. On the falling edge of CS, a conversion process begins.
GND 2 PWR The ground return for the supply and signals.
SCLK 4 Digital I/O Digital clock input. This clock directly controls the conversion and readout processes.
SDATA 5 Digital I/O Digital data output. The output samples are clocked out of this pin on falling edges of the SCLK
pin.
VA1 PWR Positive supply pin. This pin must be connected to a quiet 2.7-V to 5.25-V 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.
VIN 3 Analog I/O Analog input. This signal can range from 0 V to VA.
PAD PWR For package suffix CISD(X) only, TI recommends connecting the center pad to ground.
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(1) Stresses beyond those listed under Absolute Maximum Ratings may cause permanent damage to the device. These are stress ratings
only, which do not imply functional operation of the device at these or any other conditions beyond those indicated under Recommended
Operating Conditions. Exposure to absolute-maximum-rated conditions for extended periods may affect device reliability.
(2) If Military/Aerospace specified devices are required, please contact the TI Sales Office/ Distributors for availability and specifications.
(3) All voltages are measured with respect to GND = 0 V, unless otherwise specified.
(4) When the input voltage at any pin exceeds the power supply (that is, VIN < GND or VIN > VA), the current at that pin must 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 VApin. The current into the VApin is
limited by the Analog Supply Voltage specification.
(5) 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 (RθJA), and the ambient temperature (TA), and can be calculated using the formula
PDmax = (TJmax TA) / RθJA. The values for maximum power dissipation listed above is reached only when the device is operated in a
severe fault condition (for example, when input or output pins are driven beyond the power supply voltages, or the power supply polarity
is reversed). Obviously, such conditions must always be avoided.
7 Specifications
7.1 Absolute Maximum Ratings
over operating free-air temperature range (unless otherwise noted)(1)(2)(3)
MIN MAX UNIT
Analog supply voltage, VA–0.3 6.5 V
Voltage on any digital pin to GND –0.3 6.5 V
Voltage on any analog pin to GND –0.3 VA+ 0.3 V
Input current at any pin(4) ±10 mA mA
Package input current(4) ±20 mA mA
Power consumption at TA= 25°C See (5)
Junction temperature, TJ150 °C
Storage temperature, Tstg –65 150 °C
(1) JEDEC document JEP155 states that 500-V HBM allows safe manufacturing with a standard ESD control process.
(2) HBM is 100-pF capacitor discharged through a 1.5-kresistor.
(3) JEDEC document JEP157 states that 250-V CDM allows safe manufacturing with a standard ESD control process.
(4) Machine model is 220-pF discharged through 0 Ω.
7.2 ESD Ratings VALUE UNIT
V(ESD) Electrostatic discharge Human-body model (HBM), per ANSI/ESDA/JEDEC JS-001(1)(2) ±3500 VCharged-device model (CDM), per JEDEC specification JESD22-C101(3) ±1250
Machine mode (MM)(4) ±300
(1) All voltages are measured with respect to GND = 0 V, unless otherwise specified.
(2) Regardless of supply voltage
7.3 Recommended Operating Conditions
over operating free-air temperature range (unless otherwise noted)(1)
MIN MAX UNIT
Operating temperature, TA–40 85 °C
Supply voltage, VA2.7 5.25 V
Digital input pins voltage(2) –0.3 5.25 V
Analog input pins voltage 0 VAV
Clock frequency 0.025 20 MHz
Sample rate 1 Msps
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(1) For more information about traditional and new thermal metrics, see the Semiconductor and IC Package Thermal Metrics application
report, SPRA953.
(2) Soldering process must comply with Reflow Temperature Profile specifications. See http://www.ti.com/lit/SNOA549. Reflow temperature
profiles are different for lead-free and non-lead-free packages.
7.4 Thermal Information
THERMAL METRIC(1)(2) ADC121S021
UNITDBV (SOT-23) NGF (WSON)
6 PINS 6 PINS
RθJA Junction-to-ambient thermal resistance 185 83.7 °C/W
RθJC(top) Junction-to-case (top) thermal resistance 156.5 72.1 °C/W
RθJB Junction-to-board thermal resistance 29.6 24.8 °C/W
ψJT Junction-to-top characterization parameter 33.8 3.4 °C/W
ψJB Junction-to-board characterization parameter 29.1 24.7 °C/W
RθJC(bot) Junction-to-case (bottom) thermal resistance 14.8 °C/W
(1) Tested limits are specified to TI's AOQL (Average Outgoing Quality Level).
(2) Data sheet min/max specification limits are ensured by design, test, or statistical analysis.
7.5 Electrical Characteristics
VA= 2.7 V to 5.25 V, fSCLK = 1 MHz to 4 MHz, fSAMPLE = 50 ksps to 200 ksps, CL= 15 pF, unless otherwise noted. Typical
limits apply for TA= 25°C; minimum and maximum limits apply for TA= –40°C to 85°C, unless otherwise noted. All limits(1)(2)(2)
PARAMETER TEST CONDITIONS MIN TYP MAX UNIT
STATIC CONVERTER CHARACTERISTICS
Resolution with
no missing codes TA= –40°C to 85°C 12 Bits
INL Integral non-linearity VA= 2.7 V to 3.6 V TA= 25°C –0.4 0.45 LSB
TA= –40°C to 85°C –1 1
VA= 4.75 V to 5.25 V TA= 25°C –0.4 0.55 LSB
DNL Differential non-linearity VA= 2.7 V to 3.6 V TA= 25°C –0.25 0.45 LSB
TA= –40°C to 85°C –0.8 1
VA= 4.75 V to 5.25 V TA= 25°C –0.3 0.6 LSB
VOFF Offset error VA= 2.7 V to 3.6 V –0.18 ±1.2 LSB
VA= 4.75 V to 5.25 V TA= 25°C –0.26
GE Gain error VA= 2.7 V to 3.6 V –0.75 ±1.5 LSB
VA= 4.75 V to 5.25 V TA= 25°C –1.6
DYNAMIC CONVERTER CHARACTERISTICS
SINAD Signal-to-noise plus
distortion ratio VA= 2.7 V to 5.25 V, fIN = 100 kHz, –0.02 dBFS 70 72 dBFS
SNR Signal-to-noise ratio VA= 2.7 V to 5.25 V, fIN = 100 kHz, –0.02 dBFS 70.8 72.3 dBFS
THD Total harmonic distortion VA= 2.7 V to 5.25 V, fIN = 100 kHz, –0.02 dBFS –83 dBFS
SFDR Spurious-free dynamic range VA= 2.7 V to 5.25 V, fIN = 100 kHz, –0.02 dBFS 85 dB
ENOB Effective number of bits VA= 2.7 V to 5.25 V, fIN = 100 kHz, –0.02 dBFS 11.3 11.7 Bits
IMD
Intermodulation distortion,
second order terms VA= 5.25 V, fa= 103.5 kHz, fb= 113.5 kHz –83 dBFS
Intermodulation distortion,
third order terms VA= 5.25 V, fa= 103.5 kHz, fb= 113.5 kHz –82 dBFS
FPBW –3-dB full power bandwidth VA= 5 V 11 MHz
VA= 3 V 8
ANALOG INPUT CHARACTERISTICS
VIN Input range TA= 25°C 0 VAV
IDCL DC leakage current –1 1 µA
CINA Input capacitance Track Mode 30 pF
Hold Mode 4
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Electrical Characteristics (continued)
VA= 2.7 V to 5.25 V, fSCLK = 1 MHz to 4 MHz, fSAMPLE = 50 ksps to 200 ksps, CL= 15 pF, unless otherwise noted. Typical
limits apply for TA= 25°C; minimum and maximum limits apply for TA= –40°C to 85°C, unless otherwise noted. All limits(1)(2)(2)
PARAMETER TEST CONDITIONS MIN TYP MAX UNIT
(3) 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.
(4) Required by bus relinquish and the start of the next conversion.
DIGITAL INPUT CHARACTERISTICS
VIH Input high voltage VA= 5.25 V TA= –40°C to 85°C 2.4 V
VA= 3.6 V TA= –40°C to 85°C 2.1
VIL Input low voltage VA= 5 V TA= –40°C to 85°C 0.8 V
VA= 3 V TA= –40°C to 85°C 0.4
IIN Input current VIN = 0 V or VA±0.1 ±1 µA
CIND Digital input capacitance 2 4 pF
DIGITAL OUTPUT CHARACTERISTICS
VOH Output high voltage ISOURCE = 200 µA VA 0.2 VA 0.07 V
ISOURCE = 1 mA VA 0.1
VOL Output low voltage ISINK = 200 µA 0.03 0.4 V
ISINK = 1 mA 0.1
IOZH, IOZL TRI-STATE®leakage current ±0.1 ±10 µA
COUT TRI-STATE output
capacitance 2 4 pF
Output coding Straight (Natural) Binary
POWER SUPPLY CHARACTERISTICS
VASupply voltage 2.7 5.25 V
IA
Supply current, normal mode
(operational, CS low) VA= 5.25 V, fSAMPLE = 200 ksps 1.5 2.8 mA
VA= 3.6 V, fSAMPLE = 200 ksps 0.4 1.2
Supply current, shutdown
(CS high) fSCLK = 0 MHz, VA= 5.25 V, fSAMPLE = 0 ksps 500 nA
fSCLK = 4 MHz, VA= 5.25 V, fSAMPLE= 0 ksps 60 µA
PD
Power consumption,
normal mode
(operational, CS low)
VA= 5.25 V 7.9 14.7 mW
VA= 3.6 V 1.5 4.3
Power consumption,
shutdown
(CS high)
fSCLK = 0 MHz, VA= 5.25 V, fSAMPLE = 0 ksps 2.6 µW
VA= 5.25 V, fSCLK = 4 MHz, fSAMPLE= 0 ksps 315
AC ELECTRICAL CHARACTERISTICS
fSCLK Clock frequency(3) 1 4 MHz
fSSample rate(3) 50 200 ksps
DC SCLK duty cycle fSCLK = 4 MHz 40% 50% 60%
tACQ Minimum acquisition time 350 ns
tQUIET Minimum quiet time(4) 50 ns
tAD Aperture delay 3 ns
tAJ Aperture jitter 30 ps
Z2 Z1 Z0 DB11 DB3 DB2 DB1 DB0
tQUIET
Track
3 leading zero bits 12 data bits
CS
SCLK
SDATA
1 2 3 4 5 12 13 14 15 16
TRI-STATE
||
|
tSU tCL
tEN tCH tACC tHtDIS
tCS
Hold
tACQ
17 18 19 20
7
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(1) Measured with the timing test circuit shown in Figure 12 and defined as the time taken by the output signal to cross 1 V.
(2) Measured with the timing test circuit shown in Figure 12 and defined as the time taken by the output signal to cross 1 V or 2 V.
(3) tDIS is derived from the time taken by the outputs to change by 0.5 V with the timing test circuit shown in Figure 12. The measured
number is then adjusted to remove the effects of charging or discharging the output capacitance. This means that tDIS is the true bus
relinquish time, independent of the bus loading.
7.6 Timing Requirements
The following specifications apply for VA= 2.7 V to 5.25 V, GND = 0 V, fSCLK = 1 MHz to 4 MHz, CL= 25 pF, fSAMPLE = 50 ksps
to 200 ksps, all limits TA= –40°C to 85°C unless otherwise noted. MIN TYP MAX UNIT
tCS Minimum CS pulse width 10 ns
tSU CS to SCLK setup time 10 ns
tEN Delay from CS until SDATA TRI-STATE disabled(1) 20 ns
tACC Data access time after SCLK falling edge(2) VA= 2.7 V to 3.6 V 40 ns
VA= 4.75 V to 5.25 V 20
tCL SCLK low pulse width 0.4 × tSCLK ns
tCH SCLK high pulse width 0.4 × tSCLK
tHSCLK to data valid hold time VA= 2.7 V to 3.6 V 7 ns
VA= 4.75 V to 5.25 V 5
tDIS SCLK falling edge to
SDATA high impedance(3) VA= 2.7 V to 3.6 V 6 25 ns
VA= 4.75 V to 5.25 V 5 25
tPOWER-UP Power-up time from full power-down TA= 25°C 1 µs
Figure 1. ADC121S021 Serial Timing Diagram
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7.7 Typical Characteristics
TA= 25°C, fSAMPLE = 50 ksps to 200 ksps, fSCLK = 1 MHz to 4 MHz, fIN = 100 kHz unless otherwise stated.
fSCLK = 1 MHz
Figure 2. DNL
fSCLK = 1 MHz
Figure 3. INL
fSCLK = 4 MHz
Figure 4. DNL
fSCLK = 4 MHz
Figure 5. INL
Figure 6. DNL vs Clock Frequency Figure 7. INL vs Clock Frequency
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Typical Characteristics (continued)
TA= 25°C, fSAMPLE = 50 ksps to 200 ksps, fSCLK = 1 MHz to 4 MHz, fIN = 100 kHz unless otherwise stated.
Figure 8. SNR vs Clock Frequency Figure 9. SFDR vs Clock Frequency
Figure 10. THD vs Clock Frequency
fSCLK = 4 MHz
Figure 11. Power Consumption vs Throughput
8 Parameter Measurement Information
Figure 12. Timing Test Circuit
T/H
12-BIT
SUCCESSIVE
APPROXIMATION
ADC
SCLK
CS
SDATA
CONTROL
LOGIC
VIN
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9 Detailed Description
9.1 Overview
The ADC121S021 is a low-power, single-channel, 12-bit analog-to-digital converter which is based upon a
successive-approximation register architecture with an internal track-and-hold circuit. It operates with a
singlesupply voltage that can range from 2.7 V to 5.25 V. The ADC121S021 is packaged in 6-pin WSON and
SOT-23 package. Operation over the industrial temperature range of –40C to 85C is ensured.
9.2 Functional Block Diagram
9.3 Feature Description
The ADC121S021 is fully specified over a sample rate range of 50 ksps to 200 ksps. Normal power consumption
of the device using a 3.6-V or 5.25-V supply is 1.5 mW and 7.9 mW, respectively. The power-down feature helps
reduce the power consumption to as low as 2.6 µW using a 5.25-V supply. The output serial data is straight
binary, and is compatible with several standards such as SPI, QSPI, MICROWIRE, and many common DSP
serial interfaces.
9.4 Device Functional Modes
The ADC has two possible modes of operation: normal mode, and shutdown mode. The ADC enters normal
mode (and a conversion process is begun) when CS is pulled low. The device enters shutdown mode if CS is
pulled high before the 10th falling edge of SCLK after CS is pulled low, or stays in normal mode if CS remains
low. When in shutdown mode, the device stays there until CS is brought low again. By varying the ratio of time
spent in the normal and shutdown modes, a system may trade off throughput for power consumption, with a
sample rate as low as zero.
9.4.1 Normal Mode
The fastest possible throughput is obtained by leaving the ADC in normal mode at all times, so there are no
power-up delays. To keep the device in normal mode continuously, CS must be kept low until after the 10th
falling edge of SCLK after the start of a conversion (remember that a conversion is initiated by bringing CS low).
If CS is brought high after the 10th falling edge, but before the 16th falling edge, the device remains in normal
mode, but the current conversion aborts, and SDATA returns to TRI-STATE (truncating the output word).
Sixteen SCLK cycles are required to read all of a conversion word from the device. After sixteen SCLK cycles
have elapsed, CS may be idled either high or low until the next conversion. If CS is idled low, it must be brought
high again before the start of the next conversion, which begins when CS is again brought low.
After sixteen SCLK cycles, SDATA returns to TRI-STATE. Another conversion may be started, after tQUIET has
elapsed, by bringing CS low again.
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Device Functional Modes (continued)
9.4.2 Shutdown Mode
Shutdown mode is appropriate for applications that either do not sample continuously, or it is acceptable to trade
throughput for power consumption. When the ADC is in shutdown mode, all of the analog circuitry is turned off.
To enter shutdown mode, a conversion must be interrupted by bringing CS high anytime between the second
and 10th falling edges of SCLK, as shown in Figure 13. Once CS has been brought high in this manner, the
device enters shutdown mode; the current conversion is aborted and SDATA enters TRI-STATE. If CS is brought
high before the second falling edge of SCLK, the device does not change mode; this is to avoid accidentally
changing mode as a result of noise on the CS line.
Figure 13. Entering Shutdown Mode
Figure 14. Entering Normal Mode
To exit shutdown mode, bring CS back low. Upon bringing CS low, the ADC begins powering up (power-up time
is specified in Timing Requirements). This power-up delay results in the first conversion result being unusable.
The second conversion performed after power-up, however, is valid, as shown in Figure 14.
If CS is brought back high before the 10th falling edge of SCLK, the device returns to shutdown mode. This is
done to avoid accidentally entering normal mode as a result of noise on the CS line. To exit shutdown mode and
remain in normal mode, CS must be kept low until after the 10th falling edge of SCLK. The ADC is fully powered
up after 16 SCLK cycles.
GND
SAMPLING
CAPACITOR
SW1 -
+CONTROL
LOGIC
CHARGE
REDISTRIBUTION
DAC
SW2
VIN
VA
2
GND
SAMPLING
CAPACITOR
SW1 -
+CONTROL
LOGIC
CHARGE
REDISTRIBUTION
DAC
SW2
VIN
VA
2
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10 Applications Information
NOTE
Information in the following applications sections is not part of the TI component
specification, and TI does not warrant its accuracy or completeness. TI’s customers are
responsible for determining suitability of components for their purposes. Customers should
validate and test their design implementation to confirm system functionality.
10.1 Application Information
The ADC121S021 is a successive-approximation analog-to-digital converter designed around a charge-
redistribution digital-to-analog converter core. Simplified schematics of the ADC121S021 in both track and hold
modes are shown in Figure 15 and Figure 16, respectively. In Figure 15, the device is in track mode: switch SW1
connects the sampling capacitor to the input, and SW2 balances the comparator inputs. The device is in this
state until CS is brought low, at which point the device moves to the hold mode.
Figure 16 shows the device 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 or subtract fixed amounts of charge from 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 device moves from hold mode to track mode on the 13th rising edge of SCLK.
Figure 15. ADC121S021 in Track Mode
Figure 16. ADC121S021 in Hold Mode
10.1.1 Using the ADC121S021
The serial interface timing diagram for the ADC is shown in Figure 1. CS is chip select, which initiates
conversions on the ADC and frames the serial data transfers. SCLK (serial clock) controls both the conversion
process and the timing of serial data. SDATA is the serial data out pin, where a conversion result is found as a
serial data stream.
Basic operation of the ADC begins with CS going low, which initiates a conversion process and data transfer.
Subsequent rising and falling edges of SCLK is labeled with reference to the falling edge of CS; for example, the
third falling edge of SCLK shall refer to the third falling edge of SCLK after CS goes low.
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Application Information (continued)
At the fall of CS, the SDATA pin comes out of TRI-STATE, and the converter moves from track mode to hold
mode. The input signal is sampled and held for conversion on the falling edge of CS. The converter moves from
hold mode to track mode on the 13th rising edge of SCLK (see Figure 1). It is at this point that the interval for the
tACQ specification begins. At least 350 ns must pass between the 13th rising edge of SCLK and the next falling
edge of CS. The SDATA pin is placed back into TRI-STATE after the 16th falling edge of SCLK, or at the rising
edge of CS, whichever occurs first. After a conversion is completed, the quiet time (tQUIET) must be satisfied
before bringing CS low again to begin another conversion.
Sixteen SCLK cycles are required to read a complete sample from the ADC. The sample bits (including leading
zeroes) are clocked out on falling edges of SCLK, and are intended to be clocked in by a receiver on subsequent
rising edges of SCLK. The ADC produces three leading zero bits on SDATA, followed by twelve data bits, most
significant first.
If CS goes low before the rising edge of SCLK, an additional (fourth) zero bit may be captured by the next falling
edge of SCLK.
10.1.1.1 Determining Throughput
Throughput depends on the frequency of SCLK and how much time is allowed to elapse between the end of one
conversion and the start of another. At the maximum specified SCLK frequency, the maximum ensured
throughput is obtained by using a 20 SCLK frame. As shown in Figure 1, the minimum allowed time between CS
falling edges is determined by 1) 12.5 SCLKs for Hold mode, 2) the larger of two quantities: either the minimum
required time for Track mode (tACQ) or 2.5 SCLKs to finish reading the result and 3) 0, 1/2 or 1 SCLK padding to
ensure an even number of SCLK cycles so there is a falling SCLK edge when CS next falls. For example, at the
fastest rate for this family of parts, SCLK is 20 MHz and 2.5 SCLKs are 125 ns, so the minimum time between
CS falling edges is calculated in Equation 1:
12.5 SCLKs + tACQ + 1/2 SCLK = 12.5 × 50 ns + 350 ns + 0.5 × 50 ns = 1000 ns (1)
Which corresponds to a maximum throughput of 1 MSPS. At the slowest rate for this family, SCLK is 1 MHz.
Using a 20 cycle conversion frame as shown in Figure 1 yields a 20 μs time between CS falling edges for a
throughput of 50 KSPS.
It is possible, however, to use fewer than 20 clock cycles provided the timing parameters are met. With a 1-MHz
SCLK, there are 2500 ns in 2.5 SCLK cycles, which is greater than tACQ. After the last data bit has come out, the
clock needs one full cycle to return to a falling edge. Thus the total time between falling edges of CS is
12.5 × 1 μs + 2.5 × 1 μs + 1 × 1 μs = 16 μs which is a throughput of 62.5 ksps.
VIN
D1
R1
C2
26 pF
VA
D2
C1
4 pF
Conversion Phase - Switch Open
Track Phase - Switch Closed
000...001
000...010
0V
011...111
111...000
000...000
111...111
111...110
ADC CODE
ANALOG INPUT
1 LSB = VA/4096
0.5 LSB +VA-1.5 LSB
||
|
14
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Application Information (continued)
10.1.2 ADC121S021 Transfer Function
The output format of the ADC is straight binary. Code transitions occur midway between successive integer LSB
values. The LSB width for the ADC is VA/ 4096. The ideal transfer characteristic is shown in Figure 17. 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.
Figure 17. Ideal Transfer Characteristic
10.1.3 Analog Inputs
An equivalent circuit for the ADC's input is shown in Figure 18. Diodes D1 and D2 provide ESD protection for the
analog inputs. The analog input must at no time go beyond (VA+ 300 mV) or (GND 300 mV), as these ESD
diodes begins to conduct, which could result in erratic operation. For this reason, the ESD diodes must not be
used to clamp the input signal.
The capacitor C1 in Figure 18 has a typical value of 4 pF, and is mainly the package pin capacitance. Resistor
R1 is the ON-resistance of the track / hold switch, and is typically 500 . Capacitor C2 is the ADC sampling
capacitor and is typically 26 pF. The ADC delivers 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 ADC to sample AC signals. Also important when sampling dynamic signals is an anti-aliasing filter.
Figure 18. Equivalent Input Circuit
10.1.4 Digital Inputs And Outputs
The ADC digital inputs (SCLK and CS) are not limited by the same maximum ratings as the analog inputs. The
digital input pins are instead limited to 5.25 V with respect to GND, regardless of VA, the supply voltage. This
allows the ADC to be interfaced with a wide range of logic levels, independent of the supply voltage.
MICROPROCESSOR
DSP
SCLK
CS
SDATA
GND
VA
ADC121S021
LP2950 5V
1 PF0.1 PF 0.1 PF1 PF
VIN
15
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Application Information (continued)
10.1.5 Power Management
The ADC takes time to power-up, either after first applying VA, or after returning to normal mode from shutdown
mode. This corresponds to one dummy conversion for any SCLK frequency within the specifications in this
document. After this first dummy conversion, the ADC performs conversions properly.
NOTE
The tQUIET time must still be included between the first dummy conversion and the second
valid conversion.
When the VAsupply is first applied, the ADC may power up in either of the two modes: normal or shutdown. As
such, one dummy conversion must be performed after start-up, as described in the previous paragraph. The part
may then be placed into either normal mode or the shutdown mode, as described in Normal Mode and Shutdown
Mode.
When the ADC is operated continuously in normal mode, the maximum ensured throughput is fSCLK / 20 at the
maximum specified fSCLK. Throughput may be traded for power consumption by running fSCLK at its maximum
specified rate and performing fewer conversions per unit time, raising the ADC CS line after the 10th and before
the 15th fall of SCLK of each conversion. A plot of typical power consumption versus throughput is shown in
Typical 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.
NOTE
The curve of power consumption vs throughput is essentially linear. This is because the
power consumption in the shutdown mode is so small that it can be ignored for all
practical purposes.
10.2 Typical Application
A typical application of the ADC is shown in Figure 19. 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 ADC. Because the reference for
the ADC is the supply voltage, any noise on the supply degrades the noise performance of the device. 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 ADC supply pin. Because of the ADC's low power requirements, it is also possible
to use a precision reference as a power supply to maximize performance. The three-wire interface is shown
connected to a microprocessor or DSP.
Figure 19. Typical Application Circuit
10.2.1 Design Requirements
A positive supply only data acquisition system capable of digitizing signals ranging from 0 V to 5 V and
interfacing through SPI with an MCU whose supply is set at 3.3 V.
16
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Typical Application (continued)
10.2.2 Detailed Design Procedure
The signal range requirement forces the design to use 5-V analog supply at VA, analog supply. This follows from
the fact that VAis also a reference potential for the ADC.
Sampling is in fact a modulation process which may result in aliasing of the input signal if the input signal is not
adequately band limited. The maximum sampling rate (fS) of the ADC121S021 when it is enabled is:
fS= fSCLK / 16 (2)
In order to avoid aliasing, the Nyquist criterion has to be met:
BWsignal < fS/ 2 (3)
Therefore it is necessary to place an anti-aliasing filter at the input of the ADC. This filter may be a single-pole
low-pass filter. The pole location need to satisfy Equation 4:
1 / (π× R ×C) < fSCLK / 16 (4)
With fSCLK = 4 MHz, a good choice for the single pole filter is:
R = 100 Ω
C = nF
This reduces the input BWsignal = 250 kHz. The capacitor at the VIN input of the device provides not only the
filtering of the input signal, but it also absorbs the charge kick-back from the ADC. The kick-back is the result of
the internal switches opening at the end of the acquisition period.
Take care when the signal source is capable of producing voltages beyond VA. In such instances the internal
ESD diodes may start conducting. The ESD diodes are not intended as input signal clamps. To provide the
desired clamping action use Schottky diodes.
10.2.3 Application Curves
Figure 20. SINAD vs Clock Frequency
VA= 5.25 V fSCLK = 4 MHz
Figure 21. Spectral Response
CS
SDATA
SCLK
VA
GND
C1
VIN
RC2
17
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11 Power Supply Recommendations
The ADC requires a single voltage supply within 2.7 V and 5.25 V.
11.1 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 causes 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 dumps current
into the die substrate, which is resistive. Load discharge currents causes ground bounce noise in the substrate
that degrades noise performance if that current is large enough. The larger 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. It is good practice
to use a 100-series resistor at the ADC output, located as close to the ADC output pin as practical. This limits
the charge and discharge current of the output capacitance and improve noise performance.
12 Layout
12.1 Layout Guidelines
Ground must be a low impedance connection for return currents to flow undisturbed back to their respective
sources. Keep connections to the ground plane as short and direct as possible. When using vias to connect to
the ground layer, use multiple vias in parallel to reduce impedance to ground.
A mixed-signal layout sometimes incorporates separate analog and digital ground planes that are tied together at
one location; however, separating the ground planes is not necessary when analog, digital, and power supply
circuitry into different PCB regions to prevent digital return currents from coupling into sensitive analog circuitry.
For best performance, dedicate an entire PCB layer to a ground plane and do not route any other signal traces
on this layer. If ground plane separation is necessary, then make the connection at the ADC. Do not connect
individual ground planes at multiple locations because this configuration creates ground loops. A single plane for
analog and digital ground avoids ground loops.
If isolation is required in the application, isolate the digital signals between the ADC and controller, or provide the
isolation form the controller to the remaining system. If an external crystal is used to provide the ADC clock,
place the crystal and load capacitors directly to the ADC pins using short direct traces.
Supply pins must be bypassed with a low-ESR ceramic capacitor. Place the bypass capacitors as close as
possible to the supply pins using short, direct traces. For optimum performance, use low-impedance connections
on the ground-side connections of the bypass capacitors. Flow the supply current through the bypass capacitor
pin first and then to the supply pin to make the bypassing most effective (also known as a Kelvin connection). If
multiple ADCs are on the same PCB, use wide power supply traces or dedicated power-supply planes to
minimize the potential of crosstalk between ADCs.
It is important that the SCLK input of the serial interface is free from noise and glitches. Even with relatively slow
SCLK frequencies, short digital-signal rise and fall times may cause excessive ringing and noise. For best
performance, keep the digital signal traces short, use termination resistors as needed, and ensure all digital
signals are routed directly above the ground plane with minimal use of vias.
12.2 Layout Example
Figure 22. ADC1210S21 Layout Example
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13 Device and Documentation Support
13.1 Device Support
13.1.1 Device Nomenclature
ACQUISITION TIME 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. Acquisition time is measured backwards from the falling
edge of CS when the signal is sampled and the part moves from track to hold. The start of the time
interval that contains tACQ is the 13th rising edge of SCLK of the previous conversion when the part
moves from hold to track. The user must ensure that the time between the 13th rising edge of
SCLK and the falling edge of the next CS is not less than tACQ to meet performance specifications.
APERTURE DELAY The time after the falling edge of CS to when the input signal is acquired or held for
conversion.
APERTURE JITTER (APERTURE UNCERTAINTY) The variation in aperture delay from sample to sample.
Aperture jitter manifests itself as noise in the output.
CONVERSION TIME The time required, after the input voltage is acquired, for the ADC to convert the input
voltage to a digital word. This is from the falling edge of CS when the input signal is sampled to the
16th falling edge of SCLK when the SDATA output goes into TRI-STATE.
DIFFERENTIAL NON-LINEARITY (DNL) The measure of the maximum deviation from the ideal step size of 1
LSB.
DUTY CYCLE 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) 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 A measure of the frequency at which the reconstructed output fundamental drops
3 dB below its low frequency value for a full scale input.
GAIN ERROR 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) A measure of the deviation of each individual code from a line drawn from
negative full scale LSB below the first code transition) through positive full scale 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) 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 sum of the power in both of
the original frequencies. IMD is usually expressed in dB.
MISSING CODES Output codes that never appears at the ADC outputs. The ADC121S021 is ensured not to
have any missing codes.
OFFSET ERROR 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) 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 harmonics or DC
SIGNAL TO NOISE PLUS DISTORTION (S/N+D or SINAD) 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 DC
THD = 20 log10 Af12
Af22 + + Af62
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Device Support (continued)
SPURIOUS FREE DYNAMIC RANGE (SFDR) 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) 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:
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 (5)
THROUGHPUT TIME The minimum time required between the start of two successive conversion. It is the
acquisition time plus the conversion time.
13.2 Community Resources
The following links connect to TI community resources. Linked contents are provided "AS IS" by the respective
contributors. They do not constitute TI specifications and do not necessarily reflect TI's views; see TI's Terms of
Use.
TI E2E™ Online Community TI's Engineer-to-Engineer (E2E) Community. Created to foster collaboration
among engineers. At e2e.ti.com, you can ask questions, share knowledge, explore ideas and help
solve problems with fellow engineers.
Design Support TI's Design Support Quickly find helpful E2E forums along with design support tools and
contact information for technical support.
13.3 Trademarks
SPI, QSPI, E2E are trademarks of Texas Instruments.
TRI-STATE is a registered trademark of Texas Instruments.
All other trademarks are the property of their respective owners.
13.4 Electrostatic Discharge Caution
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.
13.5 Glossary
SLYZ022 TI Glossary.
This glossary lists and explains terms, acronyms, and definitions.
14 Mechanical, Packaging, and Orderable Information
The following pages include mechanical, packaging, and orderable information. This information is the most
current data available for the designated devices. This data is subject to change without notice and revision of
this document. For browser-based versions of this data sheet, refer to the left-hand navigation.
PACKAGE OPTION ADDENDUM
www.ti.com 11-Jan-2021
Addendum-Page 1
PACKAGING INFORMATION
Orderable Device Status
(1)
Package Type Package
Drawing Pins Package
Qty Eco Plan
(2)
Lead finish/
Ball material
(6)
MSL Peak Temp
(3)
Op Temp (°C) Device Marking
(4/5)
Samples
ADC121S021CIMF NRND SOT-23 DBV 6 1000 Non-RoHS
& Green Call TI Call TI -40 to 85 X07C
ADC121S021CIMF/NOPB ACTIVE SOT-23 DBV 6 1000 RoHS & Green SN Level-1-260C-UNLIM -40 to 85 X07C
ADC121S021CIMFX/NOPB ACTIVE SOT-23 DBV 6 3000 RoHS & Green SN Level-1-260C-UNLIM -40 to 85 X07C
ADC121S021CISD/NOPB ACTIVE WSON NGF 6 1000 RoHS & Green SN Level-1-260C-UNLIM -40 to 85 X7C
ADC121S021CISDX/NOPB ACTIVE WSON NGF 6 4500 RoHS & Green SN Level-1-260C-UNLIM -40 to 85 X7C
(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 <=1000ppm threshold. Antimony trioxide based
flame retardants must also meet the <=1000ppm threshold requirement.
(3) MSL, Peak Temp. - The Moisture Sensitivity Level rating according to the JEDEC industry standard classifications, and peak solder temperature.
(4) There may be additional marking, which relates to the logo, the lot trace code information, or the environmental category on the device.
(5) Multiple Device Markings will be inside parentheses. Only one Device Marking contained in parentheses and separated by a "~" will appear on a device. If a line is indented then it is a continuation
of the previous line and the two combined represent the entire Device Marking for that device.
(6) Lead finish/Ball material - Orderable Devices may have multiple material finish options. Finish options are separated by a vertical ruled line. Lead finish/Ball material values may wrap to two
lines if the finish value exceeds the maximum column width.
PACKAGE OPTION ADDENDUM
www.ti.com 11-Jan-2021
Addendum-Page 2
Important Information and Disclaimer:The information provided on this page represents TI's knowledge and belief as of the date that it is provided. TI bases its knowledge and belief on information
provided by third parties, and makes no representation or warranty as to the accuracy of such information. Efforts are underway to better integrate information from third parties. TI has taken and
continues to take reasonable steps to provide representative and accurate information but may not have conducted destructive testing or chemical analysis on incoming materials and chemicals.
TI and TI suppliers consider certain information to be proprietary, and thus CAS numbers and other limited information may not be available for release.
In no event shall TI's liability arising out of such information exceed the total purchase price of the TI part(s) at issue in this document sold by TI to Customer on an annual basis.
TAPE AND REEL INFORMATION
*All dimensions are nominal
Device Package
Type Package
Drawing Pins SPQ Reel
Diameter
(mm)
Reel
Width
W1 (mm)
A0
(mm) B0
(mm) K0
(mm) P1
(mm) W
(mm) Pin1
Quadrant
ADC121S021CIMF SOT-23 DBV 6 1000 178.0 8.4 3.2 3.2 1.4 4.0 8.0 Q3
ADC121S021CIMF/NOPB SOT-23 DBV 6 1000 178.0 8.4 3.2 3.2 1.4 4.0 8.0 Q3
ADC121S021CIMFX/NOP
BSOT-23 DBV 6 3000 178.0 8.4 3.2 3.2 1.4 4.0 8.0 Q3
ADC121S021CISD/NOPB WSON NGF 6 1000 178.0 12.4 2.8 2.5 1.0 8.0 12.0 Q1
ADC121S021CISDX/NOP
BWSON NGF 6 4500 330.0 12.4 2.8 2.5 1.0 8.0 12.0 Q1
PACKAGE MATERIALS INFORMATION
www.ti.com 29-Sep-2019
Pack Materials-Page 1
*All dimensions are nominal
Device Package Type Package Drawing Pins SPQ Length (mm) Width (mm) Height (mm)
ADC121S021CIMF SOT-23 DBV 6 1000 210.0 185.0 35.0
ADC121S021CIMF/NOPB SOT-23 DBV 6 1000 210.0 185.0 35.0
ADC121S021CIMFX/NOP
BSOT-23 DBV 6 3000 210.0 185.0 35.0
ADC121S021CISD/NOPB WSON NGF 6 1000 210.0 185.0 35.0
ADC121S021CISDX/NOP
BWSON NGF 6 4500 367.0 367.0 35.0
PACKAGE MATERIALS INFORMATION
www.ti.com 29-Sep-2019
Pack Materials-Page 2
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PACKAGE OUTLINE
C
0.22
0.08 TYP
0.25
3.0
2.6
2X 0.95
1.45 MAX
0.15
0.00 TYP
6X 0.50
0.25
0.6
0.3 TYP
8
0 TYP
1.9
A
3.05
2.75
B
1.75
1.45
(1.1)
SOT-23 - 1.45 mm max heightDBV0006A
SMALL OUTLINE TRANSISTOR
4214840/B 03/2018
NOTES:
1. All linear dimensions are in millimeters. Any dimensions in parenthesis are for reference only. Dimensioning and tolerancing
per ASME Y14.5M.
2. This drawing is subject to change without notice.
3. Body dimensions do not include mold flash or protrusion. Mold flash and protrusion shall not exceed 0.15 per side.
4. Leads 1,2,3 may be wider than leads 4,5,6 for package orientation.
5. Refernce JEDEC MO-178.
0.2 C A B
1
34
5
2
INDEX AREA
PIN 1
6
GAGE PLANE
SEATING PLANE
0.1 C
SCALE 4.000
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EXAMPLE BOARD LAYOUT
0.07 MAX
ARROUND 0.07 MIN
ARROUND
6X (1.1)
6X (0.6)
(2.6)
2X (0.95)
(R0.05) TYP
4214840/B 03/2018
SOT-23 - 1.45 mm max heightDBV0006A
SMALL OUTLINE TRANSISTOR
NOTES: (continued)
6. Publication IPC-7351 may have alternate designs.
7. Solder mask tolerances between and around signal pads can vary based on board fabrication site.
SYMM
LAND PATTERN EXAMPLE
EXPOSED METAL SHOWN
SCALE:15X
PKG
1
34
5
2
6
SOLDER MASK
OPENING
METAL UNDER
SOLDER MASK
SOLDER MASK
DEFINED
EXPOSED METAL
METAL
SOLDER MASK
OPENING
NON SOLDER MASK
DEFINED
(PREFERRED)
SOLDER MASK DETAILS
EXPOSED METAL
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EXAMPLE STENCIL DESIGN
(2.6)
2X(0.95)
6X (1.1)
6X (0.6)
(R0.05) TYP
SOT-23 - 1.45 mm max heightDBV0006A
SMALL OUTLINE TRANSISTOR
4214840/B 03/2018
NOTES: (continued)
8. Laser cutting apertures with trapezoidal walls and rounded corners may offer better paste release. IPC-7525 may have alternate
design recommendations.
9. Board assembly site may have different recommendations for stencil design.
SOLDER PASTE EXAMPLE
BASED ON 0.125 mm THICK STENCIL
SCALE:15X
SYMM
PKG
1
34
5
2
6
MECHANICAL DATA
NGF0006A
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