FEATURES
Fast Throughput Rate: 3MSPS
Specified for V
Low Power:
13.5 mW max at 3MSPS with 3V Supplies
Wide Input Bandwidth:
70dB SNR at 1MHz Input Frequency
Flexible Power/Serial Clock Speed Management
No Pipeline Delays
High Speed Serial Interface
TM
/QSPITM/MICROWIRETM/DSP Compatible
SPI
Power Down Mode: 1µA max
8-Lead TSOT Package
8-Lead MSOP Package
APPLICATIONS
Battery-Powered Systems
Personal Digital Assistants
Medical Instruments
Mobile Communications
Instrumentation and Control Systems
Data Acquisition Systems
High-Speed Modems
Optical Sensors
of 2.35 V to 3.6V
DD
V
V
IN
REF
ADCs in 8-Lead TSOT
AD7273/AD7274
FUNCTIONAL BLOCK DIAGRAM
T/H
AD7273/AD7274
V
DD
10-/12-BIT
SUCCESSIVE
APPROXIMATION
ADC
CONTROL
LOGIC
GND
GND
SCLK
SDATA
&6
GENERAL DESCRIPTION
The AD7273/AD7274 are 10-bit and 12-bit, high speed,
low power, successive-approximation ADCs respectively.
The parts operate from a single 2.35V to 3.6 V power
supply and feature throughput rates up to 3 MSPS. The
parts contain a low-noise, wide bandwidth track/hold amplifier which can handle input frequencies in excess of
TBD MHz.
The conversion process and data acquisition are controlled
using CS and the serial clock, allowing the devices to
interface with microprocessors or DSPs. The input signal
is sampled on the falling edge of CS and the conversion is
also initiated at this point. The conversion rate is determined by the SCLK. There are no pipeline delays associated with the part.
The AD7273/AD7274 use advanced design techniques to
achieve very low power dissipation at high throughput
rates.
The reference for the parts is applied externally and can
be in the range of 1.2V to V
dynamic input range to the ADC.
REV. PrB (6/04)
Information furnished by Analog Devices is believed to be accurate and
reliable. However, no responsibility is assumed by Analog Devices for its
use, nor for any infringements of patents or other rights of third parties
which may result from its use. No license is granted by implication or
otherwise under any patent or patent rights of Analog Devices.Trademarks
and registered tradermarks are the property of their respective companies.
This allows the widest
DD.
PRODUCT HIGHLIGHTS
1. 3MSPS ADCs in an 8-lead TSOT package.
2. High Throughput with Low Power Consumption.
3. Flexible Power/Serial Clock Speed Management.
The conversion rate is determined by the serial clock
allowing the conversion time to be reduced through the
serial clock speed increase. This allows the average
power consumption to be reduced when a power-down
mode is used while not converting. The AD7273/
AD7274 features a power down modeto maximize
power efficiency at lower throughput rates. Current consumption is 1 µA max when in Power Down mode.
4. Reference can be driven up to the power supply.
5. No Pipeline Delay.
The parts feature a standard successive-approximation
ADC with accurate control of the sampling instant via a
CS input and once-off conversion control.
One Technology Way, P.O. Box 9106, Norwood, MA 02062-9106, U.S.A.
Tel: 781/329-4700World Wide Web Site: http://www.analog.com
Fax: 781/326-8703 Analog Devices, Inc., 2004
Page 2
PRELIMINARY TECHNICAL DATA
(VDD=+2.35 V to +3.6 V, V
AD7273-SPECIFICATIONS
ParameterB Grade
DYNAMIC PERFORMANCEf
Signal-to-Noise + Distortion (SINAD)
Total Harmonic Distortion (THD)
Peak Harmonic or Spurious Noise (SFDR)
Intermodulation Distortion (IMD)
2
2
-73dB max
2
2
wise noted; TA=T
1
MIN
UnitsTest Conditions/Comments
61dB min
-74dB max
to T
= +2.5V , f
REF
, unless otherwise noted.)
MAX
= 1 MHz Sine Wave
IN
=52 MHz, f
SCLK
=3 MSPS unless other-
SAMPLE
Second Order Terms -82dB typfa= TBD kHz, fb= TBD kHz
Third Order Terms -82dB typfa= TBD kHz, fb= TBD kHz
Aperture DelayTBDns typ
Aperture JitterTBDps typ
Full Power BandwidthTBDMHz typ@ 3 dB
Full Power BandwidthTBDMHz typ@ 0.1dB
Power Supply Rejection Ratio (PSRR)TBDdB typ
DC ACCURACY
Resolution10Bits
Integral Nonlinearity
Differential Nonlinearity
Offset Error
Gain Error
2
2
Total Unadjusted Error (TUE)
2
2
±0.5LSB max
±0.5LSB maxGuaranteed No Missed Codes to 10 Bits
±1LSB max
±TBDLSB typ
±1LSB max
2
±TBDLSB typ
±TBDLSB max
ANALOG INPUT
Input Voltage Range 0 to V
REF
Volts
DC Leakage Current±0.5µA max
Input CapacitanceTBDpF typ
REFERENCE INPUT
V
Input Voltage Range 1.2 to V
REF
Vmin/Vmax
DD
DC leakage Current±TBDµA max
Input CapacitanceTBDpF max
Input ImpedanceTBDkΩ typ
LOGIC INPUTS
Input High Voltage, V
INH
0.7(VDD) V min2.35V⭐ Vdd ⭐2.7V
2V min2.7V< Vdd ⭐ 3.6V
Input Low Voltage, V
INL
0.2(VDD) V max2.35V⭐Vdd< 2.7V
0.8V max2.7V ⭐Vdd⭐ 3.6V
Input Current, I
Input Current, IIN, CS Pin±TBDµA max
Input Capacitance, C
, SCLK Pin±0.5µA maxTypically TBD nA, VIN= 0 V or V
IN
IN
3
10pF max
DD
LOGIC OUTPUTS
Output High Voltage, V
Output Low Voltage, V
Floating-State Leakage Current ±1µA max
Floating-State Output Capacitance
OH VDD
0.2V maxI
OL
3
10pF max
- 0.2V minI
= 200 µA,VDD= 2.35 V to 3.6 V
SOURCE
= 200µA
SINK
Output Coding Straight (Natural) Binary
CONVERSION RATE
Conversion Time230ns max12 SCLK cycles with SCLK at 52 MHz
Track/Hold Acquisition Time
2
50ns max
Throughput Rate3MSPS max
NOTES
1
Temperature range from –40°C to +85°C.
2
See Terminology.
3
Guaranteed by Characterization.
Specifications subject to change without notice.
–2–
REV. PrB
Page 3
PRELIMINARY TECHNICAL DATA
(VDD=+2.35 V to +3.6 V, V
AD7273-SPECIFICATIONS
ParameterB Grade
otherwise noted; TA=T
1
UnitsTest Conditions/Comments
POWER REQUIREMENTS
V
DD
I
DD
2.35/3.6V min/Vmax
Normal Mode(Static)2.5mA typVDD= 2.35V to 3.6V, SCLK On or Off
Normal Mode (Operational)4.5mA maxV
Full Power-Down Mode (Static)1µA maxSCLK On or Off, typically TBD nA
Full Power-Down Mode (Dynamic) TBDmA typVDD= 3V, f
Power Dissipation
4
Normal Mode (Operational)13.5mW maxVDD=3V, f
Full Power-Down3µW maxVDD=3V
NOTES
1
Temperature range from –40°C to +85°C.
2
See Terminology.
3
Guaranteed by Characterization.
4
See Power Versus Throughput Rate section.
Specifications subject to change without notice.
MIN
= +2 .5V, f
REF
to T
, unless otherwise noted.)
MAX
=52 MHz, f
SCLK
Digital I/Ps= 0V or V
= 2.35V to 3.6V, f
DD
SAMPLE
SAMPLE
=3MSPS unless
SAMPLE
DD
SAMPLE
= 1MSPS
= 3MSPS
= 3MSPS
REV. PrB
–3–
Page 4
PRELIMINARY TECHNICAL DATA
AD7274-SPECIFICATIONS
(VDD=+2.35 V to +3.6 V, V
noted; TA=T
MIN
to T
MAX
= +2.5V, f
REF
=52 MHz, f
SCLK
, unless otherwise noted.)
=3MSPS unless otherwise
SAMPLE
Parameter B Grade1 Units Test Conditions/Comments
DYNAMIC PERFORMANCEf
Signal-to-Noise + Distortion (SINAD)
Signal-to-Noise Ratio (SNR) 71dB min
Total Harmonic Distortion (THD)
Peak Harmonic or Spurious Noise (SFDR)
Intermodulation Distortion (IMD)
2
2
2
70dB min
-80dB typ
2
-82dB typ
= 1 MHz Sine Wave
IN
Second Order Terms -84dB typfa= TBD kHz, fb= TBD kHz
Third Order Term -84dB typfa= TBD kHz, fb= TBD kHz
Aperture DelayTBDns typ
Aperture JitterTBDps typ
Full Power BandwidthTBDMHz typ @ 3 dB
Full Power BandwidthTBDMHz typ @ 0.1dB
Power Supply Rejection Ratio (PSRR)TBDdB typ
DC ACCURACY
Resolution 12Bits
Integral Nonlinearity
Differential Nonlinearity
Offset Error
Gain Error
2
2
Total Unadjusted Error (TUE)
2
2
±1LSB max
±1LSB max Guaranteed No Missed Codes to 12 Bits
±TBDLSB max
2
±TBDLSB max
±TBDLSB max
ANALOG INPUT
Input Voltage Range
0 to V
REF
Volts
DC Leakage Current±0.5µA max
Input CapacitanceTBDpF typ
REFERENCE INPUT
V
Input Voltage Range 1.2 to V
REF
Vmin/Vmax
DD
DC leakage Current ±TBDµA max
Input CapacitanceTBDpF max
Input ImpedanceTBDkΩ typ
LOGIC INPUTS
Input High Voltage, V
INH
0.7(VDD) V min2.35V⭐ Vdd ⭐2.7V
2 V min2.7V < Vdd⭐ 3.6V
Input Low Voltage, V
0.2(VDD) V max2.35V⭐Vdd< 2.7V
INL
0.8 V max2.7V ⭐Vdd⭐ 3.6V
Input Current, I
Input Current, IIN, CS Pin±TBD µA max
Input Capacitance, C
,SCLK Pin ±0.5 µA maxTypically TBD nA, VIN= 0 V or V
IN
IN
3
10 pF max
DD
LOGIC OUTPUTS
Output High Voltage, V
Output Low Voltage, V
Floating-State Leakage Current ±1µA max
Floating-State Output Capacitance
Conversion Time270 ns max14 SCLK Cycles with SCLK at 52 MHz
Track/Hold Acquisition Time
Throughput Rate3
2
50 ns max
MSPS max
See Serial Interface Section
NOTES
1
Temperature range from –40°C to +85°C.
2
See Terminology.
3
Guranteed by Characterization.
Specifications subject to change without notice.
–4–
REV. PrB
Page 5
PRELIMINARY TECHNICAL DATA
(VDD=+2.35 V to +3.6 V, V
AD7274 SPECIFICATIONS
otherwise noted; TA=T
Parameter B Grade1 Units Test Conditions/Comments
POWER REQUIREMENTS
V
DD
I
DD
2.35/3.6
V min/Vmax
Normal Mode (Static)2.5mA typVDD= 2.35V to 3.6V,SCLK On or Off
Normal Mode (Operational)4.5 mA maxV
Full Power-Down Mode(Static)1 µA maxSCLK On or Off, typically TBD nA
Full Power-Down Mode(Dynamic)TBDmA typ V
Power Dissipation
4
Normal Mode (Operational) 13.5mW max VDD= 3 V, f
Full Power-Down 3µW max V
NOTES
1
Temperature range from –40°C to +85°C.
2
See Terminology.
3
Guranteed by Characterization.
4
See Power Versus Throughput Rate section.
Specifications subject to change without notice.
MIN
= + 2.5V, f
REF
to T
, unless otherwise noted.)
MAX
=52 MHz, f
SCLK
Digital I/Ps= 0V or V
= 2.35V to 3.6V, f
DD
= 3V, f
DD
DD
= 3 V
SAMPLE
SAMPLE
SAMPLE
DD
SAMPLE
=1MSPS
= 3MSPS
=3MSPS unless
=3MSPS
REV. PrB
–5–
Page 6
PRELIMINARY TECHNICAL DATA
AD7273/AD7274
TIMING SPECIFICATIONS
Limit at T
MIN
, T
MAX
1
(VDD= +2.35 V to +3.6 V; V
= 2.5V, TA= T
REF
Preliminary Technical Data
to T
MIN
, unless otherwise noted.)
MAX
Parameter AD7273/AD7274 Units Description
f
SCLK
2
20KHz min
3
52MHz max
t
CONVERT
t
QUIET
14 x t
SCLK
12 x t
SCLK
TBDns minMinimum Quiet Time required between Bus Relinquish
AD7274
AD7273
and start of Next Conversion
t
1
t
2
4
t
3
4
t
4
t
5
t
6
4
t
7
5
t
8
t
NOTES
1
2
3
4
5
6
Specifications subject to change without notice.
6
power-up
Guaranteed by Characterization. All input signals are specified with tr=tf=5ns (10% to 90% of V
Mark/Space ratio for the SCLK input is 40/60 to 60/40.
Minimum
Measured with the load circuit of Figure 1 and defined as the time required for the output to cross the Vih or Vil voltage.
t8 is derived form the measured time taken by the data outputs to change 0.5 V when loaded with the circuit of Figure 1. The measured number
is then extrapolated back to remove the effects of charging or discharging the 25 pF capacitor. This means that the time, t
timing characteristics is the true bus relinquish time of the part and is independent of the bus loading.
See Power-up Time section.
f
10ns minMinimum CS Pulse Width
TBDns minCS to SCLK Setup Time
TBDns maxDelay from CS Until SDATA Three-State Disabled
TBDns maxData Access Time After SCLK Falling Edge
0.4t
0.4t
SCLK
SCLK
ns minSCLK Low Pulse Width
ns minSCLK High Pulse Width
TBDns minSCLK to Data Valid Hold Time
TBDns maxSCLK Falling Edge to SDATA Three-State
TBDns minSCLK Falling Edge to SDATA Three-State
TBDµs maxPower Up Time from Full Power-down
) and timed from a voltage level of 1.6Volts.
DD
at which specifications are guaranteed.
sclk
8
, quoted in the
I
OL
I
OH
OUTPUT
PIN
200µA
TO
C
L
25pF
200µA
Figure 1. Load Circuit for Digital Output
Timing Specifications
t
4
SCLK
SDAT A
Figure 2. Access time after SCLK falling edge
+1.6V
t
7
SCLK
SDAT A
V
IH
V
IL
Figure 3. Hold time after SCLK falling edge
t
SCLK
V
IH
V
IL
SDATA
8
1.6 V
Figure 4. SCLK falling edge to SDATA Three-State
–6–
REV. PrB
Page 7
PRELIMINARY TECHNICAL DATA
Preliminary Technical Data
Figures 5 and 6 show some of the timing parameters from the Timing Specifications table.
&6
t
convert
t
2
SCLK
SDATA
THREESTAT E
151315
t
3
ZEROZ
2 LEADING
ZERO’S
Timing Example 1
From Figure 6, having f
333 ns. With t
Figure 6 shows that, t
ns for t
QUIET
= TBD ns min, this leaves t
2
ACQ
satisfying the minimum requirement of TBD ns.
2
3
DB11DB9ZEROZERODB0
DB10
Figure 5. AD7274 Serial Interface Timing Diagram
= 52 MHz and a throughput of 3MSPS, gives a cycle time of t2 + 12.5(1/f
SCLK
comprises of 2.5(1/f
t
6
416
t
4
ACQ
t
7
1/ THROUGHPUT
to be TBD ns. This TBD ns satisfies the requirement of 50 ns for t
) + t8 + t
SCLK
B
14
t
5
DB1
2 TRAILING
, where t8 = TBD ns max. This allows a value of TBD
QUIET
ZERO’S
t
8
THREE-STATE
AD7273/AD7274
t
1
t
quiet
SCLK
) + t
ACQ
ACQ
=
.
Timing Example 2
Having f
With t
2
Figure 6, t
t
satisfying the minimum requirement of TBD ns.
QUIET
= 20 MHz and a throughput of 1.5 MSPS, gives a cycle time of t2 + 12.5(1/f
SCLK
= TBD ns min, this leaves t
comprises of 2.5(1/f
ACQ
&6
t
SCLK
2
1
2
to be TBD ns. This TBD ns satisfies the requirement of 50 ns for t
ACQ
) + t8 + t
SCLK
tconvert
34
12.5(1/fSCLK)
Figure 6. Serial Interface Timing Example
) + t
SCLK
, where t8 = TBD ns max. This allows a values of TBD ns for
QUIET
ACQ
t
1
= 666 ns.
ACQ
B
5
12
13
1/THROUGHPUT
14
1516
t
8
tacquisition
tquiet
. From
REV. PrB
–7–
Page 8
PRELIMINARY TECHNICAL DATA
AD7273/AD7274
ABSOLUTE MAXIMUM RATINGS
(TA = +25°C unless otherwise noted)
VDD to GND......................................-0.3 V to TBD V
Analog Input Voltage to GND......–0.3 V to V
Reference Input Voltage to GND...–0.3 V to V
Digital Input Voltage to GND..............–0.3 V to TBD V
Digital Output Voltage to GND....–0.3 V to V
Input Current to Any Pin Except Supplies
Operating Temperature Range
Commercial (B Grade)......................–40°C to +85°C
Storage Temperature Range..............–65°C to +150°C
Stresses above those listed under “Absolute Maximum Ratings” may
cause permanent damage to the device. This is a stress rating only and
functional operation of the device at these or any other conditions above
those listed in the operational sections of this specification is not implied.
Exposure to absolute maximum rating conditions for extended periods
may affect device reliability.
2
Transient currents of up to 100 mA will not cause SCR latch up.
V
SDATA
GND
1
DD
&6
2
3
4
AD7273/
AD7274
TOP VIEW
(Not to Scale)
8
7
6
5
8-lead MSOP
V
IN
GND
SCLK
V
REF
V
SDATA
GND
V
1
DD
IN
2
3
4
AD7273/
AD7274
TOP VIEW
(Not to Scale)
8
7
6
5
8-lead TSOT
GND
&6
SCLK
V
REF
ORDERING GUIDE
TemperatureLinearityPackagePackageBranding
ModelRangeError (LSB)
1
OptionDescriptionInformation
AD7274BUJ-REEL–40°C to +85°C ±1 maxUJ-8TSOTTBD
AD7274BRM–40°C to +85°C ±1 maxRM-8MSOPTBD
AD7273BUJ-REEL–40°C to +85°C±0.5 maxUJ-8TSOTTBD
AD7273BRM–40°C to +85°C±0.5 maxRM-8MSOPTBD
NOTES
1
Linearity error here refers to integral nonlinearity.
CAUTION
ESD (electrostatic discharge) sensitive device. Electrostatic charges as high as 4000 V readily
accumulate on the human body and test equipment and can discharge without detection.
Although the AD7273/AD7274 feature proprietary ESD protection circuitry, permanent damage may occur on devices subjected to high energy electrostatic discharges. Therefore, proper
ESD precautions are recommended to avoid performance degradation or loss of functionality.
–8–
REV. PrB
Page 9
PRELIMINARY TECHNICAL DATA
Preliminary Technical Data
PIN FUNCTION DESCRIPTION
Pin
MnemonicFunction
CSChip Select. Active low logic input. This input provides the dual function of initiating
conversion on the AD7273/AD7274 and also frames the serial data transfer.
V
DD
GNDAnalog Ground. Ground reference point for all circuitry on the AD7273/AD7274. All
V
IN
V
REF
SDATAData Out. Logic output. The conversion result from the AD7273/AD7274 is provided on
SCLKSerial Clock. Logic input. SCLK provides the serial clock for accessing data from the part.
Power Supply Input. The VDD range for the AD7273/AD7274 is from +2.35V to +3.6V.
analog input signals should be referred to this GND voltage.
Analog Input. Single-ended analog input channel. The input range is 0 to V
Voltage Reference Input. This pin becomes the reference voltage input and an external
reference should be applied at this pin. The external reference input range is 1.2V to V
TBD µF capacitor should be tied between this pin and AGND.
this output as a serial data stream. The bits are clocked out on the falling edge of the SCLK
input. The data stream from the AD7274 consists of two leading zeros followed by the 12
bits of conversion data followed by two trailing zeros, which is provided MSB first. The data
stream from the AD7273 consists of two leading zeros followed by the 10 bits of conversion
data followed by four trailing zeros, which is provided MSB first.
This clock input is also used as the clock source for the AD7273/AD7274's conversion
process.
AD7273/AD7274
.
REF
DD
. A
REV. PrB
–9–
Page 10
PRELIMINARY TECHNICAL DATA
AD7273/AD7274
TERMINOLOGY
Integral Nonlinearity (INL)
This is the maximum deviation from a straight line passing through the endpoints of the ADC transfer function.
For the AD7273/AD7274, the endpoints of the transfer
function are zero scale, a 1/2 LSB below the first code
transition, and full scale, a point 1/2 LSB above the last
code transition.
Differential Nonlinearity (DNL)
This is the difference between the measured and the
ideal 1 LSB change between any two adjacent codes in
the ADC.
Offset Error
This is the deviation of the first code transition (00 . . .
000) to (00 . . . 001) from the ideal, i.e,
Gain Error
AGND + 0.5 LSB
This is the deviation of the last code transition (111 . . .
110) to (111 . . . 111) from the ideal, i.e, V
REF
–
1.5LSB after the offset error has been adjusted out.
Total Unadjusted Error (TUE)
This is a comprehensive specification which includes gain,
linearity and offset errors.
Track/Hold Acquisition Time
The Track/Hold acquisition time is the time required
for the output of the track/hold amplifier to reach its
final value, within ±0.5 LSB, after the end of
conversion. See Serial Interface section for more details.
Signal to Noise Ratio (SNR)
This is the measured ratio of signal to noise at the
output to the A/D converter. The signal is the rms value
of the sine wave input. Noise is the rms quantization
error within the Nyquist bandwitdh (fs/2). The rms
value of a sine wave is one half its peak to peak value
divided by √2 and the rms value for the quantization
noise is q/√12. The ratio is dependant on the number of
quantization levels in the digitization process; the more
levels, the smaller the quantization noise. For an ideal
N-bit converter, the SNR is defined as:
SNR = 6.02 N + 1.76 dB
Thus for a 12-bit converter this is 74 dB, for a 10-bit
converter it is 62 dB.
Practically, though, various error sources in the ADC
cause the measured SNR to be less than the theoretical
value. These errors occur due to integral and differential
nonlinearities, internal AC noise sources, etc.
Signal-to- (Noise + Distortion) Ratio (SINAD)
This is the measured ratio of signal to (noise +
distortion) at the output of the A/D converter. The
signal is the rms value of the sine wave and noise is the
rms sum of all nonfundamentals signals up to half the
sampling frequency (fs/2), including harmonics but
excluding dc.
.
Preliminary Technical Data
Total Harmonic Distortion (THD)
Total harmonic distortion is the ratio of the rms sum of
harmonics to the fundamental. It is defined as:
2
2
2
2
V
+V
+V
2
THD (dB ) = 20 log
where V
V
3
is the rms amplitude of the fundamental and V2,
1
, V4, V5 and V6 are the rms amplitudes of the second
3
+V
4
V
1
through the sixth harmonics.
Peak Harmonic or Spurious Noise (SFDR)
Peak harmonic or spurious noise is defined as the ratio of
the rms value of the next largest component in the ADC
output spectrum (up to f
/2 and excluding dc) to the rms
S
value of the fundamental. Normally, the value of this
specification is determined by the largest harmonic in the
spectrum, but for ADCs where the harmonics are buried
in the noise floor, it will be a noise peak.
Intermodulation Distortion (IMD)
With inputs consisting of sine waves at two frequencies, fa
and fb, any active device with nonlinearities will create
distortion products at sum and difference frequencies of
mfa ± nfb where m, n = 0, 1, 2, 3, etc. Intermodulation
distortion terms are those for which neither m nor n are
equal to zero. For example, the second order terms include (fa + fb) and (fa – fb), while the third order terms
include (2fa + fb), (2fa – fb), (fa + 2fb) and (fa – 2fb).
The AD7273/AD7274 are tested using the CCIF standard
where two input frequencies are used (see fa and fb in the
specification page). In this case, the second order terms
are usually distanced in frequency from the original sine
waves while the third order terms are usually at a frequency close to the input frequencies. As a result, the
second and third order terms are specified separately. The
calculation of the intermodulation distortion is as per the
THD specification where it is the ratio of the rms sum of
the individual distortion products to the rms amplitude of
the sum of the fundamentals expressed in dBs.
Power Supply Rejection Ratio (PSRR)
The power supply rejection ratio is defined as the ratio of the
power in the ADC output at full-scale frequency, f, to the
power of a 200 mV p-p sine wave applied to the ADC V
supply of frequency fs.
PSRR (dB) = 10 log (Pf/ Pf
)
s
Pf is the power at frequency f in the ADC output; Pfs is
the power at frequency f
coupled onto the ADC V
s
supply.
Aperture Delay
This is the measured interval between the leading edge of the
sampling clock and the point at which the ADC actually takes
the sample.
Aperture Jitter
This is the sample-to-sample variation in the effective point
in time at which the sample is taken.
2
+V
5
6
DD
DD
–10–
REV. PrB
Page 11
PRELIMINARY TECHNICAL DATA
Preliminary Technical Data
CIRCUIT INFORMATION
The AD7273/AD7274 are high speed, low power, 10-/12Bit, single supply, analog-to-digital converters (ADC)
respectively. The parts can be operated from a +2.35V to
+3.6V supply. When operated from any supply voltage
within this range, the AD7273/AD7274 are capable of
throughput rates of 3 MSPS when provided with a 52
MHz clock.
The AD7273/AD7274 provide the user with an on-chip
track/hold, A/D converter, and a serial interface housed in
an 8-lead TSOT or an 8-lead MSOP package, which
offers the user considerable space saving advantages over
alternative solutions. The serial clock input accesses data
from the part but also provides the clock source for the
successive-approximation A/D converter. The analog
input range is 0 to V
by the ADC and this reference can be in the range of 1.2V
.
to V
DD
The AD7273/AD7274 also feature a Power-Down option
to allow power saving between conversions. The power
down feature is implemented across the standard serial
interface as described in the Modes of Operation section.
CONVERTER OPERATION
The AD7273/AD7274 is a successive-approximation analog-to-digital converter based around a charge redistribution DAC. Figures 7 and 8 show simplified schematics of
the ADC. Figure 7 shows the ADC during its acquisition
phase. SW2 is closed and SW1 is in position A, the com-
SAMPLING
CAPACI TOR
SW1
A
AGND
B
ACQUISITION
VDD / 2
V
IN
Figure 7. ADC Acquisition Phase
. An external reference is required
REF
SW2
PHASE
COMPARATOR
CHARGE
REDISTR IBUT I ON
DAC
CONT RO L
LOGI C
AD7273/AD7274
When the ADC starts a conversion, see Figure 8, SW2
will open and SW1 will move to position B causing the
comparator to become unbalanced. The Control Logic
and the Charge Redistribution DAC are used to add and
subtract fixed amounts of charge from the sampling capacitor to bring the comparator back into a balanced condition. When the comparator is rebalanced the conversion
is complete. The Control Logic generates the ADC output code. Figure 9 shows the ADC transfer function.
CHARGE
REDISTRIBUTION
SAMPLING
CAPACITOR
V
A
IN
SW1
AGND
B
CONVERSION
PHASE
V
DD
SW2
COMPARATOR
/ 2
Figure 8. ADC Conversion Phase
ADC TRANSFER FUNCTION
The output coding of the AD7273/AD7274 is straight
binary. The designed code transitions occur midway
between succesive integer LSB values, i.e, 0.5LSB,
1.5LSBs, etc. The LSB size is V
/1024 for the AD7273. The ideal transfer characteris-
V
REF
/4096 for the AD7274,
REF
tic for the AD7273/AD7274 is shown in Figure 9.
111...111
111...110
E
D
111...000
O
C
C
011...111
D
A
000...010
000...001
000...000
0V
0.5LSB
ANALOG INPUT
1LSB = V
1LSB = V
+VDD-1.5LSB
REF
REF
DAC
CONTROL
LOGIC
/4096 (AD7274)
/1024 (AD7273)
REV. PrB
Figure 9. AD7273/AD7274 Transfer Characteristic
–11–
Page 12
PRELIMINARY TECHNICAL DATA
AD7273/AD7274
PERFORMANCE CURVES
Dynamic Performance curves
TPC 1 and TPC 2 show typical FFT plots for the AD7274
and AD7273 respectively, at 3 MSPS sample rate and TBD
KHz input tone.
TPC 3 shows the Signal-to-(Noise+Distortion) Ratio
performance versus Input frequency for various supply
voltages while sampling at 3 MSPS with a SCLK frequency
of 52 MHz for the AD7274.
TPC 4 shows the Signal to Noise Ratio (SNR) performance
versus Input frequency for various supply voltages while
sampling at 3 MSPS with a SCLK frequency of 52 MHz for
the AD7274.
TPC 5 shows a graph of the Total Harmonic Distortion
(THD) versus Analog input signal frequency for various
supply voltages while sampling at 3 MSPS with a SCLK
frequency of 52 MHz for the AD7274.
TPC 6 shows a graph of the Total Harmonic Distortion
(THD) versus Analog input frequency for different source
impedances when using a supply voltage of TBD V,SCLK
frequency of52 MHzand sampling at a rate of 3 MSPS for
the AD7274. See Analog Input section.
TPC 7 shows the Power Supply Rejection Ratio (PSRR)
versus Supply Ripple Frequency for the AD7274 when no
decoupling is used. See PSRR in the Terminology section.
Preliminary Technical Data
DC Accuracy curves
TPC 8and TPC 9 show typical INL and DNL performance
for the AD7276.
TP10 and TPC11 show Change in DNL and INL versus
Reference Voltage when using a supply voltage of 3V.
Power Requirements curves
TPC12 shows Maximum current versus Supply voltage for
the AD7274 with different SCLK frequencies.
See also Power versus Throughput Rate.
Typical Performance Characteristics
E
L
T
I
T
0
0
TPC 1. AD7274 Dynamic performance at 3 MSPS
TBD
TITLE
E
L
T
I
T
0
0
TPC 2. AD7273 Dynamic performance at 3 MSPS
TBD
TITLE
–12–
REV. PrB
Page 13
PRELIMINARY TECHNICAL DATA
Preliminary Technical Data
E
L
T
I
T
0
0
TPC 3. AD7274 SINAD vs Analog Input Frequency
at 3 MSPS for various Supply Voltages
TBD
TITLE
AD7273/AD7274
E
L
T
I
T
0
0
TPC 6. THD vs. Analog Input Frequency
for various Source Impedance
TBD
TITLE
E
L
T
I
T
0
0
TBD
TITLE
TPC 4. AD7274 SNR vs Analog Input Frequency
at 3 MSPS for various Supply Voltages
E
L
T
I
T
TBD
E
L
T
I
T
0
0
TBD
TITLE
TPC 7. Power Supply Rejection Ratio (PSRR)
versus Supply Ripple Frequency
E
L
T
I
T
TBD
0
0
TITLE
TPC 5. THD vs. Analog Input Frequency at 3 MSPS
for various Supply Voltages
REV. PrB
–13–
0
0
TITLE
TPC 8. AD7276 INL performance
Page 14
PRELIMINARY TECHNICAL DATA
AD7273/AD7274
E
L
T
I
T
0
0
TPC 9. AD7276 DNL performance
TBD
TITLE
Preliminary Technical Data
E
L
T
I
T
0
0
TPC 12. Maximum current vs Supply voltage for
different SCLK frequencies.
TBD
TITLE
E
L
T
I
T
0
0
TBD
TITLE
TPC 10. Change in INL versus Reference Voltage
E
L
T
I
T
TBD
0
0
TITLE
TPC 11. Change in DNL versus Reference Voltage
–14–
REV. PrB
Page 15
PRELIMINARY TECHNICAL DATA
Preliminary Technical Data
TYPICAL CONNECTION DIAGRAM
Figure 10 shows a typical connection diagram for the
AD7273/AD7274. An external reference must be applied
to the ADC. This reference can be in the range of 1.2V to
. A precision reference like the REF19X family or the
V
DD
ADR421 can be used to supply the reference voltage to the
AD7273/AD7274.
The conversion result is output in a 16-bit word with two
leading zeros followed by the 12-bit or 10-bit result. The
12-bit result from the AD7274 will be followed by two
trailing zeros and the 10-bit result from the AD7273 will
be followed by four trailing zeros.
Table I provides some typical performance data with
various references under the same set-up conditions.
Figure 11 shows an equivalent circuit of the analog input
structure of the AD7273/AD7274. The two diodes D1 and
D2 provide ESD protection for the analog inputs. Care
must be taken to ensure that the analog input signal never
exceeds the supply rails by more than 300mV. This will
cause these diodes to become forward biased and start
conducting current into the substrate. 10mA is the maximum current these diodes can conduct without causing
irreversable damage to the part. The capacitor C1 in
Figure 11 is typically about 4pF and can primarily be
attributed to pin capacitance. The resistor R1 is a lumped
component made up of the on resistance of a switch. This
resistor is typically about TBDΩ.
The capacitor C2 is the
ADC sampling capacitor and has a capacitance of TBD
pF typically. For ac applications, removing high
frequency components from the analog input signal is
recommended by use of a bandpass filter on the relevant
analog input pin. In applications where harmonic distortion and signal to noise ratio are critical, the analog input
should be driven from a low impedance source. Large
source impedances will significantly affect the ac performance of the ADC. This may necessitate the use of an
input buffer amplifier. The choice of the op-amp will be a
function of the particular application.
V
DD
D1
V
IN
C1
4pF
D2
CONVERSION PHASE - SWITCH OPEN
TRACKPHA SE-SWITCH CLOSED
R1
C2
TBD PF
Figure 11. Equivalent Analog Input Circuit
REV. PrB
–15–
Page 16
PRELIMINARY TECHNICAL DATA
AD7273/AD7274
Table II provides some typical performance data with
various op-amps used as the input buffer under the same
set-up conditions.
Op-amp in the AD7274 SNR Performance
input buffer TBD kHz Input
AD8510 TBD dB
AD8610 TBD dB
AD8038 TBD dB
AD8519 TBD dB
Table II. AD7274 performance for various Input Buffers
When no amplifier is used to drive the analog input, the
source impedance should be limited to low values. The
maximum source impedance will depend on the amount
of total harmonic distortion (THD) that can be
tolerated. The THD will increase as the source
impedance increases and performance will degrade. See
TPC6.
Digital Inputs
The digital inputs applied to the AD7273/AD7274 are not
limited by the maximum ratings which limit the analog
inputs. Instead, the digitals inputs applied can go to TBD
V and are not restricted by the V
analog inputs. For example, if the AD7273/AD7274 were
operated with a V
of 3V then 5V logic levels could be
DD
used on the digital inputs. However, it is important to
note that the data output on SDATA will still have 3V
logic levels when V
= 3V. Another advantage of SCLK
DD
and CS not being restricted by the V
the fact that power supply sequencing issues are avoided.
If CS or SCLK are applied before V
risk of latch-up as there would be on the analog inputs if a
signal greater than 0.3V was applied prior to V
+ 0.3V limit as on the
DD
+ 0.3V limit is
DD
then there is no
DD
.
DD
Preliminary Technical Data
MODES OF OPERATION
The mode of operation of the AD7273/AD7274 is selected by controlling the logic state of the CS signal
during a conversion. There are two possible modes of
operation, Normal Mode and Power-Down Mode. The
point at which CS is pulled high after the conversion has
been initiated will determine whether the AD7273/
AD7274 will enter Power-Down Mode or not. Similarly,
if already in Power-Down then CS can control whether
the device will return to Normal operation or remain in
Power-Down. These modes of operation are designed to
provide flexible power management options. These options can be chosen to optimize the power dissipation/
throughput rate ratio for different application
requirements.
Normal Mode
This mode is intended for fastest throughput rate performance as the user does not have to worry about any
power-up times with the AD7273/AD7274 remaining fully
powered all the time. Figure 12 shows the general diagram of the operation of the AD7273/AD7274 in this
mode.
The conversion is iniated on the falling edge of CS as
described in the Serial Interface section. To ensure the
part remains fully powered up at all times CS must remain
low until at least 10 SCLK falling edges have elapsed after
the falling edge of CS. If CS is brought high any time
after the 10th SCLK falling, the part will remain powered
up but the conversion will be terminated and SDATA will
go back into three-state.
For the AD7274 a minimum of 14 serial clock cycles are
required to complete the conversion and access the
complete conversion result. For the AD7273 a minimum
of 12 serial clock cycles are required to complete the conversion and access the complete conversion result.
CS may idle high until the next conversion or may idle
low until CS returns high sometime prior to the next
conversion (effectively idling CS low).
Once a data transfer is complete (SDATA has returned to
three-state), another conversion can be initiated after the
quiet time, t
, has elapsed by bringing CS low again.
QUIET
&6
SCLK
SDATA
AD7273/74
12
1
VALID DATA
Figure 12. Normal Mode Operation
10
–16–
14
16
REV. PrB
Page 17
PRELIMINARY TECHNICAL DATA
&
6
Preliminary Technical Data
Power-Down Mode
This mode is intended for use in applications where
slower throughput rates are required; either the ADC is
powered down between each conversion, or a series of
conversions may be performed at a high throughput rate
and then the ADC is powered down for a relatively long
duration between these bursts of several conversions.
When the AD7273/AD7274 is in Power-Down, all analog
circuitry is powered down.
To enter Power-Down, the conversion process must be
interrupted by bringing CS high anywhere after the second
falling edge of SCLK and before the 10th falling edge of
SCLK as shown in Figure 13. Once CS has been brought
high in this window of SCLKs, then the part will enter
Power-Down and the conversion that was intiated by the
falling edge of CS will be terminated and SDATA will go
back into three-state. If CS is brought high before the
second SCLK falling edge, then the part will remain in
Normal Mode and will not power-down. This will avoid
accidental power-down due to glitches on the CS line.
AD7273/AD7274
In order to exit this mode of operation and power the
AD7273/AD7274 up again, a dummy conversion is performed. On the falling edge of CS the device will begin to
power up, and will continue to power up as long as CS is
held low until after the falling edge of the 10th SCLK.
The device will be fully powered up once 16 SCLKs have
elapsed and valid data will result from the next conversion
as shown in Figure 14. If CS is brought high before the
10th falling edge of SCLK, then the AD7273/AD7274
will go back into Power- Down again. This avoids accidental power up due to glitches on the CS line or an inadvertent burst of 8 SCLK cycles while CS is low. So,
although the device may begin to power up on the falling
edge of CS, it will power down again on the rising edge
of CS as long as it occurs before the 10th SCLK falling
edge.
&6
SCLK
SDATA
SCLK
SDATA
THE PART BEGINS
TO POW ER UP
A
1
2
1
10
INVALID DATA
10
INVALID DATA
THREE-STATE
Figure 13. Entering Power Down Mode
16
1
Figure 14. Exiting Power Down Mode
16
THEPARTISFULLY
POWEREDUPWITHV
FULLY ACQUIRED
VALID DATA
IN
16
REV. PrB
–17–
Page 18
PRELIMINARY TECHNICAL DATA
AD7273/AD7274
Power-up Time
The power-up time of the AD7273/AD7274 is TBD ns,
which means that with any frequency of SCLK up to 52
MHz, one dummy cycle will always be sufficient to allow
the device to power up. Once the dummy cycle is complete, the ADC will be fully powered up and the input
signal will be acquired properly. The quite time t
must still be allowed from the point where the bus goes
back into three-state after the dummy conversion, to the
next falling edge of CS. When running at 3 MSPS
throughput rate, the AD7273/AD7274 will power up and
acquire a signal within ±0.5 LSB in one dummy cycle,
i.e. TBD ns.
When powering up from the Power-Down mode with a
dummy cycle, as in Figure 14, the track and hold which
was in hold mode while the part was powered down,
returns to track mode after the first SCLK edge the part
receives after the falling edge of CS. This is shown as
point A in Figure 14. Although at any SCLK frequency
one dummy cycle is sufficient to power the device up and
acquire V
, it does not necessarily mean that a full
IN
dummy cycle of 16 SCLKs must always elapse to power
up the device and acquire V
fully; TBD ns will be suffi-
IN
cient to power the device up and acquire the input signal.
If, for example, a 25 MHz SCLK frequency was applied
to the ADC, the cycle time would be 640 ns. In one
dummy cycle, 640 ns, the part would be powered up and
acquired fully. However after TBD ns with a 25 MHz
V
IN
SCLK only TBD SCLK cycles would have elapsed. At
this stage, the ADC would be fully powered up and the
signal acquired. So, in this case the CS can be brought
high after the 10th SCLK falling edge and brought low
again after a time t
to initiate the conversion.
QUIET
When power supplies are first applied to the AD7273/
AD7274, the ADC may either power up in the PowerDown mode or in Normal mode. Because of this, it is best
to allow a dummy cycle to elapse to ensure the part is fully
powered up before attempting a valid conversion. Likewise, if it is intended to keep the part in the Power-Down
mode while not in use and the user wishes the part to
power up in Power-Down mode, then the dummy cycle
may be used to ensure the device is in Power-Down by
executing a cycle such as that shown in Figure 13. Once
supplies are applied to the AD7273/AD7274, the power
up time is the same as that when powering up from the
Power-Down mode. It takes approximately TBD ns to
power up fully if the part powers up in Normal mode. It is
not necessary to wait TBD ns before executing a dummy
cycle to ensure the desired mode of operation. Instead, the
dummy cycle can occur directly after power is supplied to
the ADC. If the first valid conversion is then performed
directly after the dummy conversion, care must be taken to
ensure that adequate acquisition time has been allowed. As
mentioned earlier, when powering up from the PowerDown mode, the part will return to track upon the first
SCLK edge applied after the falling edge of CS.
However, when the ADC powers up initially after supplies
are applied, the track and hold will already be in track.
QUIET
Preliminary Technical Data
This means, assuming one has the facility to monitor the
ADC supply current, if the ADC powers up in the desired
mode of operation and thus a dummy cycle is not required
to change mode, then neither is a dummy cycle required
to place the track and hold into track.
POWER VERSUS THROUGHPUT RATE
By using the Power-Down mode on the AD7273/AD7274
when not converting, the average power consumption of
the ADC decreases at lower throughput rates. Figure 15
shows how as the throughput rate is reduced, the device
remains in its Power-Down state longer and the average
power consumption over time drops accordingly.
For example, if the AD7273/AD7274 is operated in a
continuous sampling mode with a throughput rate of
500KSPS and a SCLK of 52MHz (V
device is placed in the Power-Down mode between
conversions, then the power consumption is calculated as
follows. The power dissipation during normal operation is
13.5 mW (V
= 3V). If the power up time is one dummy
DD
cycle, i.e. 333ns, and the remaining conversion time is
another cycle, i.e. 333ns, then the AD7273/AD7274 can
be said to dissipate 13.5mW for 666ns during each conversion cycle.If the throughput rate is 500KSPS, the cycle
time is 2µs and the average power dissipated during each
cycle is (666/2000) x (13.5 mW)= 4.5mW.
Figure 15 shows the Power vs. Throughput Rate when
using the Power-Down mode between conversions at 3V.
The Power-Down mode is intended for use with
throughput rates of approximately TBD MSPS and under
as at higher sampling rates there is no power saving made
by using the Power-Down mode.
E
L
T
I
T
0
0
Figure 15. Power vs Throughput
TBD
TITLE
= 3V), and the
DD
–18–
REV. PrB
Page 19
PRELIMINARY TECHNICAL DATA
Preliminary Technical Data
SERIAL INTERFACE
Figures 16 and 17 show the detailed timing diagram for
serial interfacing to the AD7274 and AD7273 respectively. The serial clock provides the conversion clock and
also controls the transfer of information from the
AD7273/AD7274 during conversion.
The CS signal initiates the data transfer and conversion
process. The falling edge of CS puts the track and hold
into hold mode, takes the bus out of three-state and the
analog input is sampled at this point. The conversion is
also initiated at this point.
For the AD7274 the conversion will require 14 SCLK
cycles to complete. Once 13 SCLK falling edges have
elapsed the track and hold will go back into track on the
next SCLK rising edge as shown in Figure 16 at point B.
If the rising edge of CS occurs before 14 SCLKs have
elapsed then the conversion will be terminated and the
SDATA line will go back into three-state. If 16 SCLKs
are considered in the cycle, the last two bits will be zeros
and SDATA will return to three-state on the 16th SCLK
falling edge as shown in Figure 16.
For the AD7273 the conversion will require 12 SCLK
cycles to complete. Once 11 SCLK falling edges have
elapsed, the track and hold will go back into track on the
next SCLK rising edge, as shown in Figure 17 at point B.
If the rising edge of CS occurs before 12 SCLKs have
elapsed then the conversion will be terminated and the
SDATA line will go back into three-state. If 16 SCLKs
are considered in the cycle, the AD7273 will clock out
four trailing zeros for the last four bits and SDATA will
AD7273/AD7274
return to three-state on the 16th SCLK falling edge, as
shown in Figure 17.
If the user considers a 14 SCLKs cycle serial interface for
the AD7273/AD7274, CS needs to be brought high after
the 14th SCLK falling edge, the last two trailing zeros
will be ignored and SDATA will go back into three-state.
In this case, a 45 MHz serial clock would allow to achieve
3MSPS throughput rate.
CS going low clocks out the first leading zero to be read
in by the microcontroller or DSP. The remaining data is
then clocked out by subsequent SCLK falling edges
beginning with the 2nd leading zero. Thus, the first falling clock edge on the serial clock has the first leading
zero provided and also clocks out the second leading zero.
The final bit in the data transfer is valid on the 16th falling edge, having being clocked out on the previous (15th)
falling edge.
In applications with a slower SCLK, it is possible to read
in data on each SCLK rising edge. In that case, the first
falling edge of SCLK will clock out the second leading
zero and it could be read in the first rising edge. However,
the first leading zero that was clocked out when CS went
low will be missed unless it was not read in the first falling
edge. The 15th falling edge of SCLK will clock out the
last bit and it could be read in the 15th rising SCLK edge.
If CS goes low just after one the SCLK falling edge has
elapsed, CS will clock out the first leading zero as before
and it may be read in the SCLK rising edge. The next
SCLK falling edge will clock out the second leading zero
and it could be read in the following rising edge.
&6
SCLK
SDATA
&6
SCLK
SDATA
THREE-
STAT E
THREESTATE
t
convert
t
2
151315
234
ZEROZ
DB1 0
DB11DB9ZEROZERODB0
t
3
2 LEADING
ZERO’S
t
6
t
t
4
7
1/ THROUGHPUT
DB1
B
14
t
5
2TRAILING
ZERO’S
16
t
8
THREE-STATE
t
Figure 16. AD7274 Serial Interface Timing Diagram
t
convert
t
2
1
t
3
2 LE ADING
ZERO’S
3
B
2
ZEROZ
DB9
4
101112
t
5
t
4
DB8
DB1
1/ THROUGHPUT
DB0
t
6
1315
14
t
7
ZEROZERO
4TRAILINGZERO’S
16
t
8
ZEROZERO
THREE-STATE
Figure 17. AD7273 Serial Interface Timing Diagram
quiet
t
1
t
1
t
quiet
REV. PrB
–19–
Page 20
PRELIMINARY TECHNICAL DATA
0.10
0
PR00001-0-6/04(PrB)
AD7273/AD7274
1.60 BSC
PIN 1
0.90
0.87
0.84
.10 MAX
Preliminary Technical Data
OUTLINE DIMENSIONS
Dimensions shown in millimiters
8-Lead Thin Small Outline Transistor Package [TSOT]
2.90 BSC
847
13562
1.95
BSC
0.38
0.22
(UJ- 8)
2.80 BSC
0.65 BSC
1.00 MAX
SEATING
PLANE
0.20
0.08
8°
4°
0°
0.55
0.45
0.35
COMPLIANT TO JEDEC STANDARDS MO-193BA
3.00
BSC
PIN 1
0.15
0.00
0.38
0.22
COPLANARITY
8-Lead Mini Small Outline Package [MSOP]
(RM - 8)
3.00
BSC
85
4.90
BSC
1
4
0.65 BSC
1.10 MAX
0.23
0.08
8°
0°
SEATING
PL ANE
0.80
0.60
0.40
COMPLIANT TO JEDEC STANDARDS MO-187AA
–20–
REV. PrE
Loading...
+ hidden pages
You need points to download manuals.
1 point = 1 manual.
You can buy points or you can get point for every manual you upload.