ADC10040CIMT/NOPB - NATIONAL SEMICONDUCTOR

ADC10040

ADC10040/ADC10040Q 10-Bit, 40 MSPS, 3V, 55.5 mW A/D Converter

Literature Number: SNAS224L

ADC10040/ADC10040Q

October 20, 2009

10-Bit, 40 MSPS, 3V, 55.5 mW A/D Converter

General Description

The ADC10040 is a monolithic CMOS analog-to-digital con-

verter capable of converting analog input signals into 10-bit

digital words at 40 Megasamples per second (MSPS). This

converter uses a differential, pipeline architecture with digital

error correction and an on-chip sample-and-hold circuit to

provide a complete conversion solution, and to minimize pow-

er consumption, while providing excellent dynamic perfor-

mance. A unique sample-and-hold stage yields a full-power

bandwidth of 400 MHz. Operating on a single 3.0V power

supply, this device consumes just 55.5 mW at 40 MSPS, in-

cluding the reference current. The Standby feature reduces

power consumption to just 13.5 mW.

The differential inputs provide a full scale selectable input

swing of 2.0 VP-P, 1.5 VP-P, 1.0 VP-P, with the possibility of a

single-ended input. Full use of the differential input is recom-

mended for optimum performance. An internal +1.2V preci-

sion bandgap reference is used to set the ADC full-scale

range, and also allows the user to supply a buffered refer-

enced voltage for those applications requiring increased ac-

curacy. The output data format is user choice of offset binary

or two’s complement.

The ADC10040Q runs on an Automotive Grade Flow and is

AEC-Q100 Grade 3 Qualified.

This device is available in the 28-lead TSSOP package and

will operate over the industrial temperature range of −40°C to

+85°C.

Features

■Single +3.0V operation

■Selectable 2.0 VP-P, 1.5 VP-P, or 1.0 VP-P full-scale input

swing

■400 MHz −3 dB input bandwidth

■Low power consumption

■Standby mode

■On-chip reference and sample-and-hold amplifier

■Offset binary or two’s complement data format

■Separate adjustable output driver supply to accommodate

2.5V and 3.3V logic families

■AEC-Q100 Grade 3 Qualified

■28-pin TSSOP package

Key Specifications

■Resolution 10 Bits

■Conversion Rate 40 MSPS

■Full Power Bandwidth 400 MHz

■DNL ±0.3 LSB (typ)

■SNR (fIN = 11 MHz) 59.6 dB (typ)

■SFDR (fIN = 11 MHz) −80 dB (typ)

■Power Consumption, 40 MHz 55.5 mW

Applications

■Ultrasound and Imaging

■Instrumentation

■Cellular Base Stations/Communications Receivers

■Sonar/Radar

■xDSL

■Wireless Local Loops

■Data Acquisition Systems

■DSP Front Ends

Connection Diagram

20077801

ADC10040/ADC10040Q 10-Bit, 40 MSPS, 3V, 55 mW A/D Converter

Ordering Information

Industrial (−40°C ≤ TA ≤ +85°C) NS Package Top Mark Features

ADC10040CIMT 28 Pin TSSOP ADC10040CIMT

ADC10040CIMTX 28 Pin TSSOP Tape & Reel ADC10040CIMT

ADC10040QCIMTX 28 Pin TSSOP ADC10040QCIMT AEC-Q100 Grade 3 Qualified.

Automotive Grade Production Flow

ADC10040QCIMTX 28 Pin TSSOP Tape & Reel ADC10040QCIMT AEC-Q100 Grade 3 Qualified.

Automotive Grade Production Flow

Use ADC10080EVAL Evaluation Board n/a

Block Diagram

20077802

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ADC10040/ADC10040Q

Pin Descriptions and Equivalent Circuits

Pin No. Symbol Equivalent Circuit Description

ANALOG I/O

12 VIN−

Inverting analog input signal. With a 1.2V reference the full-scale

input signal level is a differential 1.0 VP-P. This pin may be tied to

VCOM (pin 4) for single-ended operation.

13 VIN+

Non-inverting analog input signal. With a 1.2V reference the full-

scale input signal level is a differential 1.0 VP-P.

6VREF

Reference Voltage. This device provides an internal 1.2V

reference. This pin should be bypassed to VSSA with a 0.1 µF

monolithic capacitor. VREF is 1.20V nominal. This pin may be driven

by a 1.20V external reference if desired. Do not load this pin.

VREFT

VCOM

VREFB

These pins are high impedance reference bypass pins only.

Connect a 0.1 µF capacitor from each of these pins to VSSA. These

pins should not be loaded. VCOM may be used to set the input

common mode voltage VCM.

DIGITAL I/O

1 CLK

Digital clock input. The range of frequencies for this input is

20 MHz to 40 MHz. The input is sampled on the rising edge of this

input.

15 DF DF = “1” Two’s Complement

DF = “0” Offset Binary

28 STBY This is the standby pin. When high, this pin sets the converter into

standby mode. When this pin is low, the converter is in active mode.

5IRS (Input Range

Select)

IRS = “VDDA” 2.0 VP-P input range

IRS = “VSSA” 1.5 VP-P input range

IRS = “Floating” 1.0 VP-P input range

If using both VIN+ and VIN- pins, (or differential mode), then the

peak-to-peak voltage refers to the differential voltage (VIN+ - VIN-).

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ADC10040/ADC10040Q

Pin No. Symbol Equivalent Circuit Description

16–20, 23–

27 D0–D9 Digital output data. D0 is the LSB and D9 is the MSB of the binary

output word.

ANALOG POWER

2, 9, 10 VDDA

Positive analog supply pins. These pins should be connected to a

quiet 3,0V source and bypassed to analog ground with a 0.1 µF

monolithic capacitor located within 1 cm of these pins. A 4.7 µF

capacitor should also be used in parallel.

3, 11, 14 VSSA Ground return for the analog supply.

DIGITAL POWER

22 VDDIO

Positive digital supply pins for the ADC10040’s output drivers. This

pin should be bypassed to digital ground with a 0.1 µF monolithic

capacitor located within 1 cm of this pin. A 4.7 µF capacitor should

also be used in parallel. The voltage on this pin should never

exceed the voltage on VDDA by more than 300 mV.

21 VSSIO

The ground return for the digital supply for the output drivers. This

pin should be connected to the ground plane, but not near the

analog circuitry.

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ADC10040/ADC10040Q

Absolute Maximum Ratings (Note 1, Note

If Military/Aerospace specified devices are required,

please contact the National Semiconductor Sales Office/

Distributors for availability and specifications.

VDDA, VDDIO 3.9V

Voltage on Any Pin to GND −0.3V to VDDA or

VDDIO +0.3V

Input Current on Any Pin ±25 mA

Package Input Current (Note 3) ±50 mA

Package Dissipation at T = 25°C See (Note 4)

ESD Susceptibility

Human Body Model (Note 5) 2500V

Machine Model (Note 5) 250V

Soldering Temperature

Infrared, 10 sec. (Note 6) 235°C

Storage Temperature −65°C to +150°C

Operating Ratings (Note 1, Note 2)

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

VDDA (Supply Voltage) +2.7V to +3.6V

VDDIO (Output Driver Supply

Voltage) +2.5V to VDDA

VREF 1.20V

|VSSA–VSSIO|≤ 100 mV

Clock Duty Cycle 30 to 70 %

Converter Electrical Characteristics

Unless otherwise specified, the following specifications apply for VSSA = VSSIO = 0V, VDDA = +3.0V, VDDIO = +2.5V, VIN = 2 VP-P,

STBY = 0V, External VREF = 1.20V, fCLK = 40 MHz, 50% Duty Cycle, CL = 10 pF/pin. Boldface limits apply for TA = TMIN to

TMAX: all other limits TA = 25°C. (Note 9, Note 10, Note 11)

Symbol Parameter Conditions Min Typ Max Units

STATIC CONVERTER CHARACTERISTICS

No Missing Codes Guaranteed 10 Bits

INL Integral Non-Linearity FIN = 250 kHz, −0 dB Full

Scale −1.0 ±0.3 +1.0 LSB

DNL Differential Non-Linearity FIN = 250 kHz, −0 dB Full

Scale −0.9 ±0.3 +0.9 LSB

GE Gain Error Positive Error −1.5 +0.4 +1.9 % FS

Negative Error −1.5 −0.01 +1.9 % FS

OE Offset Error (VIN+ = VIN−) −1.4 0.12 +1.6 % FS

Under Range Output Code 0

Over Range Output Code 1023

FPBW Full Power Bandwidth (Note 16) 400 MHz

REFERENCE AND INPUT CHARACTERISTICS

VCM Common Mode Input Voltage 0.5 1.5 V

VCOM

Output Voltage for use as an input

common mode voltage (Note 8)

1.45 V

VREF Reference Voltage 1.2 V

VREFTC Reference Voltage Temperature

Coefficient

±80 ppm/°C

CIN VIN Input Capacitance (each pin to

VSSA)

4 pF

POWER SUPPLY CHARACTERISTICS

IVDDA Analog Supply Current STBY = 1 4.5 6.0 mA

STBY = 0 18 25 mA

IVDDIO Digital Supply Current (Note 14)STBY = 1, fIN = 0 Hz 0 mA

STBY = 0, fIN = 0 Hz 0.6 0.8 mA

PWR Power Consumption (Note 15)STBY = 1 13.5 18 mW

STBY = 0 55.5 77 mW

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ADC10040/ADC10040Q

DC and Logic Electrical Characteristics Unless otherwise specified, the following specifications apply

for VSSA = VSSIO = 0V, VDDA = +3.0V, VDDIO = +2.5V, VIN = 2 VP-P, STBY = 0V, External VREF = 1.20V, fCLK = 40 MHz, 50% Duty

Cycle, CL = 10 pF/pin. Boldface limits apply for TA = TMIN to TMAX: all other limits TA = 25°C (Note 9, Note 10, Note 11)

Symbol Parameter Conditions Min Typ Max Units

CLK, DF, STBY, SENSE

Logical “1” Input Voltage 2 V

Logical “0” Input Voltage 0.8 V

Logical “1” Input Current +10 µA

Logical “0” Input Current −10 µA

D0–D9 OUTPUT CHARACTERISTICS

Logical “1” Output Voltage IOUT = −0.5 mA VDDIO − 0.2 V

Logical “0” Output Voltage IOUT = 1.6 mA 0.4 V

DYNAMIC CONVERTER CHARACTERISTICS (Note 13)

ENOB Effective Number of Bits

fIN = 11 MHz 9.4,

9.3

9.6 Bits

fIN = 19 MHz 9.4,

9.3

9.6 Bits

SNR Signal-to-Noise Ratio

fIN = 11 MHz 58.7,

58.1

59.6 dB

fIN = 19 MHz 58.6,

59.5 dB

SINAD Signal-to-Noise Ratio + Distortion

fIN = 11 MHz 58.6,

58 59.5 dB

fIN = 19 MHz 58.5,

57.8 59.4 dB

2nd HD 2nd Harmonic

fIN = 11 MHz −75.9,

−74.7 −89 dBc

fIN = 19 MHz −74.4,

−73 −86 dBc

3rd HD 3rd Harmonic

fIN = 11 MHz −69.5,

−67.5 −78 dBc

fIN = 19 MHz −68.8,

−66.7 −77 dBc

THD Total Harmonic Distortion (First 6

Harmonics)

fIN = 11 MHz −69.5,

−67.5 −78 dB

f.IN = 19 MHz −68.8,

−66.7 −77 dB

SFDR Spurious Free Dynamic Range

(Excluding 2nd and 3rd Harmonic)

fIN = 11 MHz −75.8,

−74.5 −80 dBc

fIN = 19 MHz −75.7,

−74.3 −80 dBc

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ADC10040/ADC10040Q

AC Electrical Characteristics

Unless otherwise specified, the following specifications apply for VSSA = VSSIO = 0V, VDDA = +3.0V, VDDIO = +2.5V, VIN =

2 VP-P (full scale), STBY = 0V, External VREF = 1.20V, fCLK = 40 MHz, 50% Duty Cycle, CL = 10 pF/pin. Boldface limits apply for

TA = TMIN to TMAX: all other limits TA = 25°C (Note 10, Note 11, Note 12)

Symbol Parameter Conditions Min

(Note 12)

Typ

(Note 12)

Max

(Note 12)Units

CLK, DF, STBY, SENSE

fCLK1Maximum Clock Frequency 40 MHz (min)

fCLK2Minimum Clock Frequency 20 MHz

tCH Clock High Time 12.5 ns

tCL Clock Low Time 12.5 ns

tCONV Conversion Latency 6Cycles

tOD

Data Output Delay after a Rising Clock

Edge

T = 25°C 2 3.3 5 ns

1 6ns

tAD Aperture Delay 1 ns

tAJ Aperture Jitter 2 ps (RMS)

Over Range Recovery Time

Differential VIN step from

±3V to 0V to get accurate

conversion

1 Clock Cycle

tSTBY Standby Mode Exit Cycle 20 Cycles

Note 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 guarantee specific performance limits. For guaranteed specifications and test conditions, see the Electrical Characteristics. The guaranteed

specifications apply only for the test conditions listed. Some performance characteristics may degrade when the device is not operated under the listed test

conditions.

Note 2: All voltages are measured with respect to GND = VSSA = VSSIO = 0V, unless otherwise specified.

Note 3: When the voltage at any pin exceeds the power supplies (VIN < VSSA or VIN > VDDA), the current at that pin should be limited to 25 mA. The 50 mA maximum

package input current rating limits the number of pins that can safely exceed the power supplies with an input current of 25 mA to two.

Note 4: 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. In the 28-

pin TSSOP, θJA is 96°C/W, so PDMAX = 1,302 mW at 25°C and 677 mW at the maximum operating ambient temperature of 85°C. Note that the power dissipation

of this device under normal operation will typically be about 55.5 mW. The values for maximum power dissipation listed above will be reached only when the

ADC10040 is operated in a severe fault condition.

Note 5: Human body model is 100 pF capacitor discharged through a 1.5 kΩ resistor. Machine model is 220 pF discharged through 0Ω.

Note 6: The 235°C reflow temperature refers to infrared reflow. For Vapor Phase Reflow (VPR) the following conditions apply: Maintain the temperature at the

top of the package body above 183°C for a minimum of 60 seconds. The temperature measured on the package body must not exceed 220°C. Only one excursion

above 183°C is allowed per reflow cycle.

Note 7: The analog inputs are protected as shown below. Input voltage magnitude up to 500 mV beyond the supply rails will not damage this device. However,

input errors will be generated if the input goes above VDDA or VDDIO and below VSSA or VSSIO.

20077807

Note 8: VCOM is a typical value, measured at room temperature. It is not guaranteed by test. Do not load this pin.

Note 9: To guarantee accuracy, it is required that |VDDA–VDDIO| ≤ 100 mV and separate bypass capacitors are used at each power supply pin.

Note 10: With the test condition for 2 VP-P differential input, the 10-bit LSB is 1.95 mV.

Note 11: Typical figures are at TA = TJ = 25°C and represent most likely parametric norms. Test limits are guaranteed to National's AOQL (Average Outgoing

Quality Level).

Note 12: Timing specifications are tested at TTL logic levels, VIL = 0.4V for a falling edge, and VIH = 2.4V for a rising edge.

Note 13: Optimum dynamic performance will be obtained by keeping the reference input in the +1.2V.

Note 14: VDDIO is the current consumed by the switching of the output drivers and is primarily determined by load capacitance on the output pins, the supply

voltage, VDR, and the rate at which the outputs are switching (which is signal dependent). IDR = VDR x (C0 x f0 + C1 x f1 + C2 + f2 +....C11 x f11) where VDR is the

output driver supply voltage, Cn is the total load capacitance on the output pin, and fn is the average frequency at which the pin is toggling.

Note 15: Power consumption includes output driver power. (fIN = 0 MHz).

Note 16: The input bandwidth is limited using a capacitor between VIN− and VIN+.

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ADC10040/ADC10040Q

Specification Definitions

APERTURE DELAY is the time after the rising edge of the

clock to when the input signal is acquired or held for conver-

sion.

APERTURE JITTER (APERTURE UNCERTAINTY) is the

variation in aperture delay from sample to sample. Aperture

jitter manifests itself as noise in the output.

COMMON MODE VOLTAGE (VCM) is the d.c. potential

present at both signal inputs to the ADC.

CONVERSION LATENCY See PIPELINE DELAY.

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 specifi-

cation here refers to the ADC clock input signal.

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 states 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 from the ideal slope of the

transfer function. It can be calculated as:

Gain Error = Pos. Full-Scale Error − Neg. Full-Scale Error

INTEGRAL NON LINEARITY (INL) is a measure of the de-

viation of each individual code from a line drawn from negative

full scale through positive full scale. The deviation of any given

code from this straight line is measured from the center of that

code value.

MISSING CODES are those output codes that will never ap-

pear at the ADC outputs. The ADC10040 is guaranteed not

to have any missing codes.

NEGATIVE FULL SCALE ERROR is the difference between

the input voltage (VIN+ − VIN−) just causing a transition from

negative full scale to the first code and its ideal value of

0.5 LSB.

OFFSET ERROR is the input voltage that will cause a tran-

sition from a code of 01 1111 1111 to a code of 10 0000 0000.

OUTPUT DELAY is the time delay after the rising edge of the

clock before the data update is presented at the output pins.

PIPELINE DELAY (LATENCY) is the number of clock cycles

between initiation of conversion and when that data is pre-

sented to the output driver stage. Data for any given sample

is available at the output pins the Pipeline Delay plus the Out-

put Delay after the sample is taken. New data is available at

every clock cycle, but the data lags the conversion by the

pipeline delay.

POSITIVE FULL SCALE ERROR is the difference between

the actual last code transition and its ideal value of 1½ LSB

below positive full scale.

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 sam-

pling frequency, not including harmonics or DC.

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 com-

ponents below half the clock frequency, including harmonics

but excluding d.c.

SPURIOUS FREE DYNAMIC RANGE (SFDR) is the differ-

ence, expressed in dB, between the rms values of the input

signal and the peak spurious signal, where a spurious signal

is any signal present in the output spectrum that is not present

at the input.

TOTAL HARMONIC DISTORTION (THD) is the ratio, ex-

pressed in dBc, of the rms total of the first six harmonic levels

at the output to the level of the fundamental at the output. THD

is calculated as:

where f1 is the RMS power of the fundamental (output) fre-

quency and f2 through f6 are the RMS power in the first 6

harmonic frequencies.

SECOND HARMONIC DISTORTION (2ND HARM) is the dif-

ference expressed in dB, between the RMS power in the input

frequency at the output and the power in its 2nd harmonic

level at the output.

THIRD HARMONIC DISTORTION (3RD HARM) is the dif-

ference, expressed in dB, between the RMS power in the

input frequency at the output and the power in its 3rd harmonic

level at the output.

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ADC10040/ADC10040Q

Timing Diagram

20077809

FIGURE 1. Clock and Data Timing Diagram

Transfer Characteristics

20077810

FIGURE 2. Input vs. Output Transfer Characteristic

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ADC10040/ADC10040Q

Typical Performance Characteristics Unless otherwise specified, the following specifications apply:

VSSA = VSSIO = 0V, VDDA = +3.0V, VDDIO = +2.5V, VIN = 2 VP-P, STBY = 0V, External VREF = 1.2V, fCLK = 40 MHz, fIN = 19 MHz,

50% Duty Cycle.

DNL

20077812

DNL vs. fCLK

20077815

DNL vs. Clock Duty Cycle (DC input)

20077813

DNL vs. Temperature

20077816

INL

20077814

INL vs. fCLK

20077817

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ADC10040/ADC10040Q

INL vs. Clock Duty Cycle

20077818

SNR vs. VDDIO

20077819

SNR vs. VDDA

20077820

SNR vs. fCLK

20077821

INL vs. Temperature

20077822

SNR vs. Clock Duty Cycle

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ADC10040/ADC10040Q

SNR vs. Temperature

20077824

THD vs. VDDA

20077825

THD vs. VDDIO

20077826

THD vs. fCLK

20077827

SNR vs. IRS

20077828

THD vs. IRS

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ADC10040/ADC10040Q

SINAD vs. VDDA

20077830

SINAD vs. VDDIO

20077831

THD vs. Clock Duty Cycle

20077832

SINAD vs. Clock Duty Cycle

20077833

THD vs. Temperature

20077834

SINAD vs. Temperature

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ADC10040/ADC10040Q

SINAD vs. fCLK

20077836

SFDR vs. VDDIO

20077837

SINAD vs. IRS

20077838

SFDR vs. fCLK

20077839

SFDR vs. VDDA

20077840

SFDR vs. IRS

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ADC10040/ADC10040Q

SFDR vs. Clock Duty Cycle

20077842

Spectral Response @ 11 MHz Input

20077843

SFDR vs. Temperature

20077844

Spectral Response @ 19 MHz Input

20077845

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ADC10040/ADC10040Q

Functional Description

The ADC10040 uses a pipeline architecture and has error

correction circuitry to help ensure maximum performance.

Differential analog input signals are digitized to 10 bits. In dif-

ferential mode , each analog input signal should have a peak-

to-peak voltage equal to 1.0V, 0.75V or 0.5V, depending on

the state of the IRS pin (pin 5), and be centered around VCM

and be 180° out of phase with each other. If single ended

operation is desired, VIN- may be tied to the VCOM pin (pin 4).

A single ended input signal may then be applied to VIN+, and

should have an average value in the range of VCM. The signal

amplitude should be 2.0V, 1.5V or 1.0V peak-to-peak, de-

pending on the state or the IRS pin (pin 5).

Applications Information

1.0 ANALOG INPUTS

The ADC10040 has two analog signal inputs, VIN+ and VIN−.

These two pins form a differential input pair. There is one

common mode pin VCOM that may be used to set the common

mode input voltage.

1.1 REFERENCE PINS

The ADC10040 is designed to operate with an internal or ex-

ternal 1.2V reference. The internal 1.2V reference is the

defualt condition. If an external voltage is applied to the

VREF pin, then that voltage is used for the reference. The

VREF pin should be bypassed to ground with a 0.1 µF capacitor

placed close to the pin. Do not load this pin when using the

internal reference.

The voltages at VCOM, VREFT, and VREFB are derived from the

reference voltage. These pins are made available for bypass

purposes only. These pins should each be bypassed to

ground with a 0.1 µF capacitor placed close to the pin. It is

very important that all grounds associated with the reference

voltage and the input signal make connection to the analog

ground plane at a single point to minimize the effects of noise

currents in the ground path. DO NOT LOAD these pins.

1.2 VCOM PIN

This pin supplies a voltage for possible use to set the common

mode input voltage. This pin may also be connected to VIN-,

so that VIN+ may be used as a single ended input. These pins

should be bypassed with at least a 0.1uF capacitor. Do not

load this pin.

1.3 SIGNAL INPUTS

The signal inputs are VIN+ and VIN−. The input signal ampli-

tude is defined as VIN+ − VIN− and is represented schemati-

cally in Figure 3:

20077847

FIGURE 3. Input Voltage Waveforms for a 2VP-P

differential Input

20077848

FIGURE 4. Input Voltage Waveform for a 2VP-P Single

Ended Input

A single ended input signal is shown in Figure 4.

The internal switching action at the analog inputs causes en-

ergy to be output from the input pins. As the driving source

tries to compensate for this, it adds noise to the signal. To

minimize the effects of this, use 18Ω series resistors at each

of the signal inputs with a 25 pF capacitor across the inputs,

as shown in Figure 5. These components should be placed

close to the ADC because the input pins of the ADC is the

most sensitive part of the system and this is the last opportu-

nity to filter the input. The two 16Ω resistors and the 24 pF

capacitor, together with the 4 pF ADC input capacitance, form

a low-pass filter with a -3 dB frequency of 177 MHz.

1.4 CLK PIN

The CLK signal controls the timing of the sampling process.

Drive the clock input with a stable, low jitter clock signal in the

frequency range indicated in the AC Electrical Characteristics

Table with rise and fall times of less than 2 ns. The trace car-

rying the clock signal should be as short as possible and

should not cross any other signal line, analog or digital, not

even at 90°. The CLK signal also drives an internal state ma-

chine. If the CLK is interrupted, or its frequency is too low, the

charge on internal capacitors can dissipate to the point where

the accuracy of the output data will degrade. This is what limits

the lowest sample rate. The duty cycle of the clock signal can

affect the performance of any A/D Converter. Because

achieving a precise duty cycle is difficult, the ADC10040 is

designed to maintain performance over a range of duty cy-

cles. While it is specified and performance is guaranteed with

a 50% clock duty cycle, performance is typically maintained

with minimum clock low and high times indicated in the AC

Electrical Characteristics Table. Both minimum high and low

times may not be held simultaneously.

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ADC10040/ADC10040Q

1.5 STBY PIN

The STBY pin, when high, holds the ADC10040 in a power-

down mode to conserve power when the converter is not

being used. The power consumption in this state is 13.5 mW.

The output data pins are undefined in this mode. Power con-

sumption during power-down is not affected by the clock

frequency, or by whether there is a clock signal present. The

data in the pipeline is corrupted while in the power down.

1.6 DF PIN

The DF (Data Format) pin, when high, forces the ADC10040

to output the 2’s complement data format. When DF is tied

low, the output format is offset binary.

1.7 IRS PIN

The IRS (Input Range Select) pin defines the input signal am-

plitude that will produce a full scale output. The table below

describes the function of the IRS pin.

TABLE 1. IRS Pin Functions

IRS Pin Full-Scale Input

VDDA 2.0VP-P

VSSA 1.5VP-P

Floating 1.0VP-P

1.8 OUTPUT PINS

The ADC10040 has 10 TTL/CMOS compatible Data Output

pins. The offset binary data is present at these outputs while

the DF and STBY pins are low. Be very careful when driving

a high capacitance bus. The more capacitance the output

drivers must charge for each conversion, the more instanta-

neous digital current flows through VDDIO and VSSIO. These

large charging current spikes can cause on-chip noise and

couple into the analog circuitry, degrading dynamic perfor-

mance. Adequate bypassing, limiting output capacitance and

careful attention to the ground plane will reduce this problem.

Additionally, bus capacitance beyond the specified

10 pF/pin will cause tOD to increase, making it difficult to prop-

erly latch the ADC output data. The result could be an appar-

ent reduction in dynamic performance. To minimize noise due

to output switching, minimize the load currents at the digital

outputs. This can be done by minimizing load capacitance

and by connecting buffers between the ADC outputs and any

other circuitry, which will isolate the outputs from trace and

other circuit capacitances and limit the output currents, which

could otherwise result in performance degradation. Only one

driven input should be connected to the ADC output pins.

While the tOD time provides information about output timing,

a simple way to capture a valid output is to latch the data on

the rising edge of the conversion clock.

1.9 APPLICATION SCHEMATICS

The following figures show simple examples of using the

ADC10040. The ADC10040 performs best with a differential

input signal.

1.9.1 Narrow Band A.C. Signals

Figure 5 shows a typical circuit for an AC coupled, differen-

tially driven input. The 16Ω resistors and 24 pF capacitor,

together with the 4 pF input capacitance of the ADC10040,

provides a −3dB input bandwidth of 177 MHz, while the 0.1µF

capacitor at VCOM stabilizes the common move voltage at the

transformer center tap.

17 www.national.com

ADC10040/ADC10040Q

20077849

FIGURE 5. A Simple Application Using a Differential Signal Source

1.9.2 D.C. Applications

For very low frequency and DC input applications, a d.c. cou-

pled amplifier or buffer may be needed, especially when the

input is single-ended and the advantages of a differential input

signal is desired. Figure 6 shows the input drive circuit that

can be used to replace the transformer of Figure 5. The

LMH6550 provides excellent performance and is well-suited

for this application. The common mode output voltage of the

LMH6550 is the same as its VCM input.

20077851

FIGURE 6. Using the LMH6550 for DC and wideband

applications

1.9.3 Single Ended Applications

Performance of the ADC10040 with a single-ended input is

not as good as its performance with a differential input. How-

ever, if the lower performance is adequate, the circuit of

Figure 7 shows an acceptable method of driving the analog

input.

www.national.com 18

ADC10040/ADC10040Q

20077850

FIGURE 7. A Simple Application Using a Single Ended Signal Source

19 www.national.com

ADC10040/ADC10040Q

Physical Dimensions inches (millimeters) unless otherwise noted

28-Lead TSSOP Package

Ordering Number ADC10040CIMT, ADC10040QCIMT

NS Package Number MTC28

www.national.com 20

ADC10040/ADC10040Q

Notes

21 www.national.com

ADC10040/ADC10040Q

Notes

ADC10040/ADC10040Q 10-Bit, 40 MSPS, 3V, 55 mW A/D Converter

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