Datasheet AD7273 Datasheet (Analog Devices)

Page 1
PRELIMINARY TECHNICAL DATA
3MSPS,10-/12-Bit
a
Preliminary Technical Data
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 mode to 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.
Page 2
PRELIMINARY TECHNICAL DATA
(VDD=+2.35 V to +3.6 V, V
AD7273-SPECIFICATIONS
Parameter B Grade
DYNAMIC PERFORMANCE f
Signal-to-Noise + Distortion (SINAD) Total Harmonic Distortion (THD) Peak Harmonic or Spurious Noise (SFDR) Intermodulation Distortion (IMD)
2
2
-73 dB max
2
2
wise noted; TA=T
1
MIN
Units Test Conditions/Comments
61 dB min
-74 dB 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 -82 dB typ fa= TBD kHz, fb= TBD kHz
Third Order Terms -82 dB typ fa= TBD kHz, fb= TBD kHz
Aperture Delay TBD ns typ Aperture Jitter TBD ps typ Full Power Bandwidth TBD MHz typ @ 3 dB Full Power Bandwidth TBD MHz typ @ 0.1dB Power Supply Rejection Ratio (PSRR) TBD dB typ
DC ACCURACY
Resolution 10 Bits Integral Nonlinearity Differential Nonlinearity Offset Error
Gain Error
2
2
Total Unadjusted Error (TUE)
2
2
±0.5 LSB max ±0.5 LSB max Guaranteed No Missed Codes to 10 Bits ±1 LSB max ±TBD LSB typ ±1 LSB max
2
±TBD LSB typ ±TBD LSB max
ANALOG INPUT
Input Voltage Range 0 to V
REF
Volts DC Leakage Current ±0.5 µA max Input Capacitance TBD pF typ
REFERENCE INPUT
V
Input Voltage Range 1.2 to V
REF
Vmin/Vmax
DD
DC leakage Current ±TBD µA max
Input Capacitance TBD pF max Input Impedance TBD k typ
LOGIC INPUTS
Input High Voltage, V
INH
0.7(VDD) V min 2.35V Vdd ⭐2.7V 2 V min 2.7V< Vdd 3.6V
Input Low Voltage, V
INL
0.2(VDD) V max 2.35VVdd< 2.7V
0.8 V max 2.7V ⭐Vdd⭐ 3.6V Input Current, I Input Current, IIN, CS Pin ±TBD µA max Input Capacitance, C
, SCLK Pin ±0.5 µA max Typically 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 ±1 µA max Floating-State Output Capacitance
OH VDD
0.2 V max I
OL
3
10 pF max
- 0.2 V min I
= 200 µA,VDD= 2.35 V to 3.6 V
SOURCE
= 200µA
SINK
Output Coding Straight (Natural) Binary
CONVERSION RATE
Conversion Time 230 ns max 12 SCLK cycles with SCLK at 52 MHz Track/Hold Acquisition Time
2
50 ns max
Throughput Rate 3 MSPS 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
Parameter B Grade
otherwise noted; TA=T
1
Units Test Conditions/Comments
POWER REQUIREMENTS
V
DD
I
DD
2.35/3.6 V min/Vmax
Normal Mode(Static) 2.5 mA typ VDD= 2.35V to 3.6V, SCLK On or Off Normal Mode (Operational) 4.5 mA max V Full Power-Down Mode (Static) 1 µA max SCLK On or Off, typically TBD nA
Full Power-Down Mode (Dynamic) TBD mA typ VDD= 3V, f
Power Dissipation
4
Normal Mode (Operational) 13.5 mW max VDD=3V, f Full Power-Down 3 µW max VDD=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 PERFORMANCE f
Signal-to-Noise + Distortion (SINAD) Signal-to-Noise Ratio (SNR) 71 dB min Total Harmonic Distortion (THD) Peak Harmonic or Spurious Noise (SFDR) Intermodulation Distortion (IMD)
2
2
2
70 dB min
-80 dB typ
2
-82 dB typ
= 1 MHz Sine Wave
IN
Second Order Terms -84 dB typ fa= TBD kHz, fb= TBD kHz
Third Order Term -84 dB typ fa= TBD kHz, fb= TBD kHz
Aperture Delay TBD ns typ Aperture Jitter TBD ps typ Full Power Bandwidth TBD MHz typ @ 3 dB Full Power Bandwidth TBD MHz typ @ 0.1dB
Power Supply Rejection Ratio (PSRR) TBD dB typ DC ACCURACY
Resolution 12 Bits Integral Nonlinearity Differential Nonlinearity
Offset Error
Gain Error
2
2
Total Unadjusted Error (TUE)
2
2
±1 LSB max ±1 LSB max Guaranteed No Missed Codes to 12 Bits ±TBD LSB max
2
±TBD LSB max ±TBD LSB max
ANALOG INPUT Input Voltage Range
0 to V
REF
Volts DC Leakage Current ±0.5 µA max Input Capacitance TBD pF typ
REFERENCE INPUT
V
Input Voltage Range 1.2 to V
REF
Vmin/Vmax
DD
DC leakage Current ±TBD µA max
Input Capacitance TBD pF max Input Impedance TBD k typ
LOGIC INPUTS Input High Voltage, V
INH
0.7(VDD) V min 2.35V Vdd ⭐2.7V 2 V min 2.7V < Vdd 3.6V
Input Low Voltage, V
0.2(VDD) V max 2.35VVdd< 2.7V
INL
0.8 V max 2.7V ⭐Vdd⭐ 3.6V
Input Current, I Input Current, IIN, CS Pin ±TBD µA max Input Capacitance, C
,SCLK Pin ±0.5 µA max Typically 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 ±1 µA max Floating-State Output Capacitance
OH
OL
3
V
- 0.2 V min I
DD
0.2 V max I
10 pF max
= 200 µA;VDD= 2.35 V to 3.6 V
SOURCE
=200 µA
SINK
Output Coding Straight (Natural) Binary CONVERSION RATE
Conversion Time 270 ns max 14 SCLK Cycles with SCLK at 52 MHz Track/Hold Acquisition Time Throughput Rate 3
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) 2.5 mA typ VDD= 2.35V to 3.6V,SCLK On or Off
Normal Mode (Operational) 4.5 mA max V
Full Power-Down Mode(Static) 1 µA max SCLK On or Off, typically TBD nA Full Power-Down Mode(Dynamic) TBD mA typ V
Power Dissipation
4
Normal Mode (Operational) 13.5 mW max VDD= 3 V, f Full Power-Down 3 µW 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
20 KHz min
3
52 MHz max
t
CONVERT
t
QUIET
14 x t
SCLK
12 x t
SCLK
TBD ns min Minimum 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
10 ns min Minimum CS Pulse Width TBD ns min CS to SCLK Setup Time TBD ns max Delay from CS Until SDATA Three-State Disabled TBD ns max Data Access Time After SCLK Falling Edge
0.4t
0.4t
SCLK SCLK
ns min SCLK Low Pulse Width
ns min SCLK High Pulse Width TBD ns min SCLK to Data Valid Hold Time TBD ns max SCLK Falling Edge to SDATA Three-State TBD ns min SCLK Falling Edge to SDATA Three-State TBD µs max Power 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
DB11 DB9 ZEROZERODB0
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
4 16
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
15 16
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
Junction Temperature..........................................150°C
8-lead TSOT Package
Thermal Impedance.................................TBD°C/W
θ
JA
θ
Thermal Impedance................................TBD°C/W
JC
1
+ 0.3 V
DD
+ 0.3 V
DD
+ 0.3 V
DD
2
..........±10 mA
PIN CONFIGURATION
AD7273/AD7274
Preliminary Technical Data
8-lead MSOP Package
θ
Thermal Impedance.................................205.9°C/W
JA
Thermal Impedance...............................43.74°C/W
θ
JC
Lead Temperature Soldering
Reflow (10-30 secs)....................................+TBD°C
ESD..................................................................TBDKV
NOTES
1
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
Temperature Linearity Package Package Branding
Model Range Error (LSB)
1
Option Description Information
AD7274BUJ-REEL –40°C to +85°C ±1 max UJ-8 TSOT TBD AD7274BRM –40°C to +85°C ±1 max RM-8 MSOP TBD AD7273BUJ-REEL –40°C to +85°C ±0.5 max UJ-8 TSOT TBD AD7273BRM –40°C to +85°C ±0.5 max RM-8 MSOP TBD
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 Mnemonic Function
CS Chip 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
GND Analog Ground. Ground reference point for all circuitry on the AD7273/AD7274. All
V
IN
V
REF
SDATA Data Out. Logic output. The conversion result from the AD7273/AD7274 is provided on
SCLK Serial 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 of 52 MHz and 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–
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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
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–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–
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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.
TBD mA
0V toV
REF192
+2.5V
1µF
TANT
INPUT
0.1µF
REF
V
IN
V
REF
GND
AD7274/
AD7273
V
DD
AD7273/AD7274
Voltage AD7274 SNR Performance Reference TBD kHz Input
AD780@2.5V TBD dB
REF192 TBD dB ADR421 TBD dB ADR291 TBD dB
Table I. AD7274 performance for various Voltage
References IC
0.1µF
SCLK
SDATA
&6
SERIAL INTERFACE
10µF
+3.6V
SUPPLY
DSP/
µC/µP
Figure 10. AD7273/AD7274 Typical Connection Diagram
Analog Input
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
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–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
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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
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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
DB11 DB9 ZEROZERODB0
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
10 11 12
t
5
t
4
DB8
DB1
1/ THROUGHPUT
DB0
t
6
13 15
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
1 3562
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–
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