ADC121S051CIMF - Texas Instruments High-Performance Analog

3 4

VACS

GND SDATA

VIN SCLK

ADC121S051

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ADC121S051 Single Channel, 200 to 500 ksps, 12-Bit A/D Converter

Check for Samples: ADC121S051

1FEATURES DESCRIPTION

The ADC121S051 is a low-power, single channel

2• Specified Over a Range of Sample Rates. CMOS 12-bit analog-to-digital converter with a high-

• 6-lead WSON and SOT-23 Packages speed serial interface. Unlike the conventional

• Variable Power Management practice of specifying performance at a single sample

rate only, the ADC121S051 is fully specified over a

• Single Power Supply with 2.7V - 5.25V Range sample rate range of 200 ksps to 500 ksps. The

• SPI™/QSPI™/MICROWIRE/DSP Compatible converter is based upon a successive-approximation

APPLICATIONS circuit.

• Portable Systems The output serial data is straight binary, and is

• Remote Data Acquisition compatible with several standards, such as SPI™,

QSPI™, MICROWIRE, and many common DSP

• Instrumentation and Control Systems serial interfaces.

KEY SPECIFICATIONS The ADC121S051 operates with a single supply that

can range from +2.7V to +5.25V. Normal power

• DNL +0.5/-0.25 LSB (typ) consumption using a +3.6V or +5.25V supply is 1.7

• INL +0.45/-0.40 LSB (typ) mW and 8.7 mW, respectively. The power-down

• SNR 72.0 dB (typ) feature reduces the power consumption to as low as

2.6 µW using a +5.25V supply.

• Power Consumption The ADC121S051 is packaged in 6-lead WSON and

– 3.6V Supply 1.7 mW (typ) SOT-23 packages. Operation over the industrial

– 5.25V Supply 8.7 mW (typ) temperature range of −40°C to +85°C is ensured.

PIN COMPATIBLE ALTERNATIVES BY RESOLUTION AND SPEED(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

(1) All devices are fully pin and function compatible.

Connection Diagram

Figure 1. 6-Lead SOT-23 or WSON

See DBV or NGF Package

1Please 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.

2All trademarks are the property of their respective owners.

Products conform to specifications per the terms of the Texas

Instruments standard warranty. Production processing does not

necessarily include testing of all parameters.

T/H

12-BIT

SUCCESSIVE

APPROXIMATION

ADC

SCLK

SDATA

CONTROL

LOGIC

VIN

ADC121S051

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Block Diagram

Figure 2.

Table 1. PIN DESCRIPTIONS AND EQUIVALENT CIRCUITS

Pin No. Symbol Description

ANALOG I/O

3 VIN Analog input. This signal can range from 0V to VA

DIGITAL I/O

4 SCLK Digital clock input. This clock directly controls the conversion and readout processes.

5 SDATA Digital data output. This clock directly controls the conversion and readout processes.

6 CS Chip select. On the falling edge of CS, a conversion process begins.

POWER SUPPLY

Positive supply pin. This pin should be connected to a quiet +2.7V to +5.25V source and

1 VAbypassed to GND with a 1 μF capacitor and a 0.1 μF monolithic capacitor located within 1

cm of the power pin.

2 GND The ground return for the supply and signals.

For package suffix CISD(X) only, it is recommended that the center pad should be

PAD GND connected to ground.

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.

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Absolute Maximum Ratings(1)(2)(3)

Analog Supply Voltage VA−0.3V to 6.5V

Voltage on Any Digital Pin to GND −0.3V to 6.5V

Voltage on Any Analog Pin to GND −0.3V to (VA+0.3V)

Input Current at Any Pin (4) ±10 mA

Package Input Current (4) ±20 mA

Power Consumption at TA= 25°C See (5)

ESD Susceptibility (6)

Human Body Model 3500V

Machine Model 300V

Junction Temperature +150°C

Storage Temperature −65°C to +150°C

(1) 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.

(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 = 0V, 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 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 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 (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.

(6) Human body model is 100 pF capacitor discharged through a 1.5 kΩresistor. Machine model is 220 pF discharged through zero ohms.

Operating Ratings(1)(2)

Operating Temperature Range −40°C ≤TA≤+85°C

VASupply Voltage +2.7V to +5.25V

Digital Input Pins Voltage Range −0.3V to +5.25V

(regardless of supply voltage)

Analog Input Pins Voltage Range 0V to VA

Clock Frequency 25 kHz to 20 MHz

Sample Rate up to 1Msps

(1) 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.

(2) All voltages are measured with respect to GND = 0V, unless otherwise specified.

Package Thermal Resistance(1)

Package θJA

6-lead WSON 94°C / W

6-lead SOT-23 265°C / W

Soldering process must comply with Reflow Temperature Profile specifications. Refer to www.ti.com and http://www.ti.com/lit/SNOA549.

(1) Reflow temperature profiles are different for lead-free and non-lead-free packages.

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ADC121S051 Converter Electrical Characteristics(1)(2)

The following specifications apply for VA= +2.7V to 5.25V, fSCLK = 4 MHz to 10 MHz, fSAMPLE = 200 ksps to 500 ksps, CL= 15

pF, unless otherwise noted. Boldface limits apply for TA= TMIN to TMAX: all other limits TA= 25°C. Limits

Symbol Parameter Conditions Typical Units

(2)

STATIC CONVERTER CHARACTERISTICS

Resolution with No Missing Codes 12 Bits

+0.45 LSB (max)

VA= +2.7V to +3.6V ±1.0

−0.40 LSB (min)

INL Integral Non-Linearity +0.75 LSB (max)

VA= +4.75 to +5.25V −0.45 LSB (min)

+0.50 +1.0 LSB (max)

VA= +2.7V to +3.6V −0.25 −0.9 LSB (min)

DNL Differential Non-Linearity +0.80 LSB (max)

VA= +4.75 to +5.25V −0.50 LSB (min)

VA= +2.7V to +3.6V −0.18 ±1.2

VOFF Offset Error LSB (max)

VA= +4.75 to +5.25V +1.9

VA= +2.7V to +3.6V −0.62 ±1.5

GE Gain Error LSB (max)

VA= +4.75 to +5.25V −1.50

DYNAMIC CONVERTER CHARACTERISTICS

VA= +2.7V to 5.25V

SINAD Signal-to-Noise Plus Distortion Ratio 72 70 dB (min)

fIN = 100 kHz, −0.02 dBFS

VA= +2.7V to 5.25V

SNR Signal-to-Noise Ratio 72 70.8 dB (min)

fIN = 100 kHz, −0.02 dBFS

VA= +2.7V to 5.25V

THD Total Harmonic Distortion −83 dB

fIN = 100 kHz, −0.02 dBFS

VA= +2.7V to 5.25V

SFDR Spurious-Free Dynamic Range 84 dB

fIN = 100 kHz, −0.02 dBFS

VA= +2.7V to 5.25V

ENOB Effective Number of Bits 11.7 11.3 Bits (min)

fIN = 100 kHz, −0.02 dBFS

Intermodulation Distortion, Second VA= +5.25V −83 dB

Order Terms fa= 103.5 kHz, fb= 113.5 kHz

IMD Intermodulation Distortion, Third Order VA= +5.25V −82 dB

Terms fa= 103.5 kHz, fb= 113.5 kHz

VA= +5V 11 MHz

FPBW -3 dB Full Power Bandwidth VA= +3V 8 MHz

ANALOG INPUT CHARACTERISTICS

VIN Input Range 0 to VAV

IDCL DC Leakage Current ±1 µA (max)

Track Mode 30 pF

CINA Input Capacitance Hold Mode 4 pF

DIGITAL INPUT CHARACTERISTICS

VA= +5.25V 2.4 V (min)

VIH Input High Voltage VA= +3.6V 2.1 V (min)

VA= +5V 0.8 V (max)

VIL Input Low Voltage VA= +3V 0.4 V (max)

IIN Input Current VIN = 0V or VA±0.1 ±1 µA (max)

CIND Digital Input Capacitance 2 4pF (max)

(1) Tested limits are specified to National's AOQL (Average Outgoing Quality Level).

(2) Data sheet min/max specification limits are ensured by design, test, or statistical analysis.

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ADC121S051 Converter Electrical Characteristics(1)(2) (continued)

The following specifications apply for VA= +2.7V to 5.25V, fSCLK = 4 MHz to 10 MHz, fSAMPLE = 200 ksps to 500 ksps, CL= 15

pF, unless otherwise noted. Boldface limits apply for TA= TMIN to TMAX: all other limits TA= 25°C. Limits

Symbol Parameter Conditions Typical Units

(2)

DIGITAL OUTPUT CHARACTERISTICS

ISOURCE = 200 µA VA−0.07 VA−0.2 V (min)

VOH Output High Voltage ISOURCE = 1 mA VA−0.1 V

ISINK = 200 µA 0.03 0.4 V (max)

VOL Output Low Voltage ISINK = 1 mA 0.1 V

IOZH, IOZL TRI-STATE® Leakage Current ±0.1 ±10 µA (max)

COUT TRI-STATE® Output Capacitance 2 4pF (max)

Output Coding Straight (Natural) Binary

POWER SUPPLY CHARACTERISTICS

2.7 V (min)

VASupply Voltage 5.25 V (max)

VA= +5.25V, 1.66 3.0 mA (max)

fSAMPLE = 200 ksps

Supply Current, Normal Mode

(Operational, CS low) VA= +3.6V, 0.46 1.3 mA (max)

fSAMPLE = 200 ksps

IAVA= +5.25V, fSCLK = 0 MHz, 500 nA

fSAMPLE = 0 ksps

Supply Current, Shutdown (CS high) VA= +5.25V, fSCLK = 10 MHz, 60 µA

fSAMPLE = 0 ksps

VA= +5.25V 8.7 15.8 mW (max)

Power Consumption, Normal Mode

(Operational, CS low) VA= +3.6V 1.7 4.7 mW (max)

VA= +5.25V, fSCLK = 0 MHz,

PD2.6 µW

fSAMPLE = 0 ksps

Power Consumption, Shutdown (CS

high) VA= +5.25V, fSCLK = 10 MHz, 315 µW

fSAMPLE = 0 ksps

AC ELECTRICAL CHARACTERISTICS

4MHz (min)

fSCLK Clock Frequency See (3) 10 MHz (max)

200 ksps (min)

fSSample Rate See (3) 500 ksps (max)

40 % (min)

DC SCLK Duty Cycle fSCLK = 10 MHz 50 60 % (max)

tACQ Minimum Time Required for Acquisition 350 ns (max)

tQUIET See (4) 50 ns (min)

tAD Aperture Delay 3 ns

tAJ Aperture Jitter 30 ps

(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) Minimum Quiet Time required by bus relinquish and the start of the next conversion.

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IOL

200 PA

IOH

200 PA

1.6 V

To Output Pin CL

25 pF

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ADC121S051 Timing Specifications

The following specifications apply for VA= +2.7V to 5.25V, GND = 0V, fSCLK = 4.0 MHz to 10.0 MHz, CL= 25 pF, fSAMPLE = 200

ksps to 500 ksps, Boldface limits apply for TA= TMIN to TMAX: all other limits TA= 25°C.

Symbol Parameter Conditions Typical Limits Units

tCS Minimum CS Pulse Width 10 ns (min)

tSU CS to SCLK Setup Time 10 ns (min)

tEN Delay from CS Until SDATA TRI-STATE Disabled (1) 20 ns (max)

VA= +2.7V to +3.6V 40 ns (max)

tACC Data Access Time after SCLK Falling Edge (2) VA= +4.75V to +5.25V 20 ns (max)

tCL SCLK Low Pulse Width 0.4 x tSCLK ns (min)

tCH SCLK High Pulse Width 0.4 x tSCLK ns (min)

VA= +2.7V to +3.6V 7ns (min)

tHSCLK to Data Valid Hold Time VA= +4.75V to +5.25V 5ns (min)

25 ns (max)

VA= +2.7V to +3.6V 6ns (min)

tDIS SCLK Falling Edge to SDATA High Impedance (3) 25 ns (max)

VA= +4.75V to +5.25V 5ns (min)

tPOWER- Power-Up Time from Full Power-Down 1 µs

(1) Measured with the timing test circuit shown in Figure 3 and defined as the time taken by the output signal to cross 1.0V.

(2) Measured with the timing test circuit shown in Figure 3 and defined as the time taken by the output signal to cross 1.0V or 2.0V.

(3) tDIS is derived from the time taken by the outputs to change by 0.5V with the timing test circuit shown in Figure 3. 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. Timing Diagrams

Figure 3. Timing Test Circuit

Product Folder Links: ADC121S051

Z2 Z1 Z0 DB11 DB3 DB2 DB1 DB0

tQUIET

Track

3 leading zero bits 12 data bits

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

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Figure 4. ADC121S051 Serial Timing Diagram

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. 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 is the time after the falling edge of CS to when the input signal is acquired or held for

conversion.

APERTURE JITTER (APERTURE UNCERTAINTY) is the variation in aperture delay from sample to sample.

Aperture jitter manifests itself as noise in the output.

CONVERSION TIME is 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) is the measure of the maximum deviation from the ideal step size of

1LSB.

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.

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 sum of the power in both of the

original frequencies. IMD is usually expressed in dB.

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‡AA++A

log20=THD 

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MISSING CODES are those output codes that will never appear at the ADC outputs. The ADC121S051 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

harmonics or d.c.

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

(1)

where Af1 is the RMS power of the input frequency at the output and Af2 through Af6 are the

RMS power in the first 5 harmonic frequencies.

THROUGHPUT TIME is the minimum time required between the start of two successive conversion. It is the

acquisition time plus the conversion time.

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Typical Performance Characteristics

TA= +25°C, fSAMPLE = 200 ksps to 500 ksps,fSCLK = 4 MHz to 10 MHz, fIN = 100 kHz unless otherwise stated.

DNL INL

fSCLK = 4 MHz fSCLK = 4 MHz

Figure 5. Figure 6.

DNL INL

fSCLK = 10 MHz fSCLK = 10 MHz

Figure 7. Figure 8.

DNL vs. Clock Frequency INL vs. Clock Frequency

Figure 9. Figure 10.

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Typical Performance Characteristics (continued)

TA= +25°C, fSAMPLE = 200 ksps to 500 ksps,fSCLK = 4 MHz to 10 MHz, fIN = 100 kHz unless otherwise stated.

SNR vs. Clock Frequency SINAD vs. Clock Frequency

Figure 11. Figure 12.

SFDR vs. Clock Frequency THD vs. Clock Frequency

Figure 13. Figure 14.

Spectral Response, VA= 5.25V Spectral Response, VA= 5.25V

fSCLK = 4 MHz fSCLK = 10 MHz

Figure 15. Figure 16.

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Typical Performance Characteristics (continued)

TA= +25°C, fSAMPLE = 200 ksps to 500 ksps,fSCLK = 4 MHz to 10 MHz, fIN = 100 kHz unless otherwise stated.

Power Consumption vs. Throughput,

fSCLK = 10 MHz

Figure 17.

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GND

SAMPLING

CAPACITOR

SW1 -

+CONTROL

LOGIC

CHARGE

REDISTRIBUTION

DAC

SW2

VIN

GND

SAMPLING

CAPACITOR

SW1 -

+CONTROL

LOGIC

CHARGE

REDISTRIBUTION

DAC

SW2

VIN

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APPLICATIONS INFORMATION

ADC121S051 OPERATION

The ADC121S051 is a successive-approximation analog-to-digital converters designed around a charge-

redistribution digital-to-analog converter core. Simplified schematics of the ADC121S051 in both track and hold

modes are shown in Figure 18 and Figure 19, respectively. In Figure 18, 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 19 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 18. ADC121S051 in Track Mode

Figure 19. ADC121S051 in Hold Mode

USING THE ADC121S051

The serial interface timing diagram for the ADC is shown in Figure 4. 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 will be labelled 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.

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 4). It is at this point that the interval for the

TACQ specification begins. In the worst case, 350ns must pass between the 13th rising edge and the next falling

edge of SCLK. The SDATA pin will be 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.

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000...001

000...010

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

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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

falling edges of SCLK. The ADC will produce 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.

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 4, 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 by:

12.5*50ns + 350ns + 0.5*50ns = 1000ns (2)

(12.5 SCLKs + tACQ + 1/2 SCLK) which corresponds to a maximum throughput of 1MSPS. At the slowest rate for

this family, SCLK is 1MHz. Using a 20 cycle conversion frame as shown in Figure 4 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 1MHz 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 will need one full cycle to return to a falling edge. Thus the

total time between falling edges of CS is 12.5*1µs +2.5*1µs +1*1µs=16 μs which is a throughput of 62.5 KSPS.

ADC121S051 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 20. 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 20. Ideal Transfer Characteristic

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VIN

26 pF

4 pF

Conversion Phase - Switch Open

Track Phase - Switch Closed

MICROPROCESSOR

DSP

SCLK

SDATA

GND

ADC121S051

LP2950 5V

1 PF0.1 PF 0.1 PF1 PF

VIN

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TYPICAL APPLICATION CIRCUIT

A typical application of the ADC is shown in Figure 21. Power is provided in this example by the National

Semiconductor 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 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 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 21. Typical Application Circuit

ANALOG INPUTS

An equivalent circuit for the ADC 's input is shown in Figure 22. Diodes D1 and D2 provide ESD protection for

the analog inputs. At no time should the analog 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, the ESD diodes should

not be used to clamp the input signal.

The capacitor C1 in Figure 22 has a typical value of 4pF, and is mainly the package pin capacitance. Resistor R1

is the on resistance of the track / hold switch, and is typically 500Ω. Capacitor C2 is the ADC sampling capacitor

and is typically 26 pF. The ADC 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 ADC to sample AC signals. Also important when sampling dynamic signals is an anti-aliasing filter.

Figure 22. Equivalent Input Circuit

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 +5.25V 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.

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MODES OF OPERATION

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 will enter shutdown mode if CS is

pulled high before the tenth falling edge of SCLK after CS is pulled low, or will stay in normal mode if CS remains

low. Once in shutdown mode, the device will stay 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.

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 will remain in normal

mode, but the current conversion will be aborted, and SDATA will return 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.

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 tenth falling edges of SCLK, as shown in Figure 23. Once CS has been brought high in this manner, the

device will enter shutdown mode; the current conversion will be aborted and SDATA will enter TRI-STATE. If CS

is brought high before the second falling edge of SCLK, the device will not change mode; this is to avoid

accidentally changing mode as a result of noise on the CS line.

Figure 23. Entering Shutdown Mode

Figure 24. Entering Normal Mode

To exit shutdown mode, bring CS back low. Upon bringing CS low, the ADC will begin powering up (power-up

time is specified in the Timing Specifications table). 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 24.

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If CS is brought back high before the 10th falling edge of SCLK, the device will return 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 will be fully

powered-up after 16 SCLK cycles.

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 will perform conversions properly. Note that 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 should 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 the

Typical Performance Characteristics section. 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 that 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.

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 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 Ωseries 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.

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SNAS302H –JULY 2005–REVISED MARCH 2013

REVISION HISTORY

Changes from Revision G (March 2013) to Revision H Page

• Changed layout of National Data Sheet to TI format .......................................................................................................... 16

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PACKAGE OPTION ADDENDUM

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Addendum-Page 1

PACKAGING INFORMATION

Orderable Device Status

(1)

Package Type Package

Drawing Pins Package

Qty Eco Plan

(2)

Lead/Ball Finish MSL Peak Temp

(3)

Op Temp (°C) Device Marking

(4/5)

Samples

ADC121S051CIMF/NOPB ACTIVE SOT-23 DBV 6 1000 Green (RoHS

& no Sb/Br) CU SN Level-1-260C-UNLIM -40 to 85 X13C

ADC121S051CIMFX/NOPB ACTIVE SOT-23 DBV 6 3000 Green (RoHS

& no Sb/Br) CU SN Level-1-260C-UNLIM -40 to 85 X13C

ADC121S051CISD/NOPB ACTIVE WSON NGF 6 1000 Green (RoHS

& no Sb/Br) CU SN Level-1-260C-UNLIM -40 to 85 X4C

ADC121S051CISDX/NOPB ACTIVE WSON NGF 6 4500 Green (RoHS

& no Sb/Br) CU SN Level-1-260C-UNLIM -40 to 85 X4C

(1) The marketing status values are defined as follows:

ACTIVE: Product device recommended for new designs.

LIFEBUY: TI has announced that the device will be discontinued, and a lifetime-buy period is in effect.

NRND: Not recommended for new designs. Device is in production to support existing customers, but TI does not recommend using this part in a new design.

PREVIEW: Device has been announced but is not in production. Samples may or may not be available.

OBSOLETE: TI has discontinued the production of the device.

(2) Eco Plan - The planned eco-friendly classification: Pb-Free (RoHS), Pb-Free (RoHS Exempt), or Green (RoHS & no Sb/Br) - please check http://www.ti.com/productcontent for the latest availability

information and additional product content details.

TBD: The Pb-Free/Green conversion plan has not been defined.

Pb-Free (RoHS): TI's terms "Lead-Free" or "Pb-Free" mean semiconductor products that are compatible with the current RoHS requirements for all 6 substances, including the requirement that

lead not exceed 0.1% by weight in homogeneous materials. Where designed to be soldered at high temperatures, TI Pb-Free products are suitable for use in specified lead-free processes.

Pb-Free (RoHS Exempt): This component has a RoHS exemption for either 1) lead-based flip-chip solder bumps used between the die and package, or 2) lead-based die adhesive used between

the die and leadframe. The component is otherwise considered Pb-Free (RoHS compatible) as defined above.

Green (RoHS & no Sb/Br): TI defines "Green" to mean Pb-Free (RoHS compatible), and free of Bromine (Br) and Antimony (Sb) based flame retardants (Br or Sb do not exceed 0.1% by weight

in homogeneous material)

(3) MSL, Peak Temp. -- The Moisture Sensitivity Level rating according to the JEDEC industry standard classifications, and peak solder temperature.

(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.

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

PACKAGE OPTION ADDENDUM

www.ti.com 7-Oct-2013

Addendum-Page 2

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)

(mm) B0

(mm) K0

(mm) P1

(mm) W

(mm) Pin1

Quadrant

ADC121S051CIMF/NOPB SOT-23 DBV 6 1000 178.0 8.4 3.2 3.2 1.4 4.0 8.0 Q3

ADC121S051CIMFX/NOP

BSOT-23 DBV 6 3000 178.0 8.4 3.2 3.2 1.4 4.0 8.0 Q3

ADC121S051CISD/NOPB WSON NGF 6 1000 178.0 12.4 2.8 2.5 1.0 8.0 12.0 Q1

ADC121S051CISDX/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 23-Sep-2013

Pack Materials-Page 1

*All dimensions are nominal

Device Package Type Package Drawing Pins SPQ Length (mm) Width (mm) Height (mm)

ADC121S051CIMF/NOPB SOT-23 DBV 6 1000 210.0 185.0 35.0

ADC121S051CIMFX/NOP

BSOT-23 DBV 6 3000 210.0 185.0 35.0

ADC121S051CISD/NOPB WSON NGF 6 1000 210.0 185.0 35.0

ADC121S051CISDX/NOP

BWSON NGF 6 4500 367.0 367.0 35.0

PACKAGE MATERIALS INFORMATION

www.ti.com 23-Sep-2013

Pack Materials-Page 2

MECHANICAL DATA

NGF0006A

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