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AD7982 Schematic ( PDF Datasheet ) - Analog Devices

Teilenummer AD7982
Beschreibung 1 MSPS PulSAR ADC
Hersteller Analog Devices
Logo Analog Devices Logo 




Gesamt 23 Seiten
AD7982 Datasheet, Funktion
www.DataSheet4U.com
18-bit, 1 MSPS PulSAR™ ADC in MSOP/QFN
Preliminary Technical Data
18-bit resolution with no missing codes
Throughput: 1MSPS
Low Power dissipation: 7.5 mW @ 1MSPS, 75 μW @ 10kSPS
INL: ±1 LSB typ, ±2.5 LSB max
Dynamic range: 99 dB
True differential analog input range: ±VREF
0 V to VREF with VREF between 2.5V to 5.0V
Any input range and easy to drive with the ADA4941
No pipeline delay
Single-supply 2.5V operation with 1.8 V/2.5 V/3 V/5 V logic
interface
Serial interface SPI®/QSPI™/MICROWIRE™/DSP-compatible
Daisy-chain multiple ADCs and BUSY indicator
10-lead package: MSOP (MSOP-8 size) and
QFN (LFCSP), 3 mm × 3 mm same space as SOT-23
APPLICATIONS
Battery-powered equipment
Data acquisitions
Instrumentation
Medical instruments
Seismic Data Acquisition Systems
Table 1. MSOP, QFN(LFCSP)/SOT-23 14, 16 and18-Bit ADC
Type
100
kSPS
250
kSPS
400-
500
kSPS
1000
kSPS
ADC
Driver
18Bit
AD76911 AD76901 AD79821 ADA4941
ADA4841
16Bit AD7680 AD76851 AD76861 AD79801 ADA4941
AD7683 AD76871 AD76881
ADA4841
AD7684 AD7694 AD76931
14Bit AD7940 AD79421 AD79461
1 Pin-for-pin compatible.
AD7982
APPLICATION DIAGRAM EXAMPLE
2.5 TO 5V 2.5V
±10V, ±5V, ..
ADA4941
REF VDD VIO
IN+ SDI
AD7982 SCK
IN–
GND
SDO
CNV
1.8 TO 5V
3- OR 4-WIRE
INTERFACE
(SPI, , CS
DAISY CHAIN)
Figure 1.
GENERAL DESCRIPTION
The AD7982 is a 18-bit, successive approximation, analog-to-
digital converter (ADC) that operates from a single power
supply, VDD. It contains a low power, high speed, 18-bit
sampling ADC and a versatile serial interface port. On the CNV
rising edge, it samples the voltage difference between IN+ and
IN− pins. The voltages on these pins usually swing in opposite
phase between 0 V and REF. The reference voltage, REF, is
applied externally and can be set independently of the supply
voltage, VDD.
Its power scales linearly with throughput.
The SPI-compatible serial interface also features the ability,
using the SDI input, to daisy chain several ADCs on a single,
3-wire bus and provides an optional BUSY indicator. It is
compatible with 1.8 V, 2.5 V, 3 V, or 5 V logic, using the separate
supply VIO.
The AD7982 is housed in a 10-lead MSOP or a 10-lead QFN
(LFCSP) with operation specified from −40°C to +85°C.
Rev PrC
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 that may result from its use.
Specifications subject to change without notice. No license is granted by implication
or otherwise under any patent or patent rights of Analog Devices. Trademarks and
registered trademarks are the property of their respective owners.
One Technology Way, P.O. Box 9106, Norwood, MA 02062-9106, U.S.A.
Tel: 781.329.4700
www.analog.com
Fax: 781.461.3113
©2006 Analog Devices, Inc. All rights reserved.






AD7982 Datasheet, Funktion
AD7982
ABSOLUTE MAXIMUM RATINGS
Preliminary Technical Data
Table 5.
Parameter
Analog Inputs
IN+1, IN−1 to GND
Supply Voltage
REF, VIO to GND
VDD to GND
VDD to VIO
Digital Inputs to GND
Digital Outputs to GND
Storage Temperature Range
Junction Temperature
θJA Thermal Impedance
θJC Thermal Impedance
Lead Temperature Range
Vapor Phase (60 sec)
Infrared (15 sec)
1 See the Analog Input section.
Rating
−0.3 V to VREF + 0.3 V
or ±130 mA
−0.3 V to +6.0V
−0.3 V to +3.0 V
+3V to −6V
−0.3 V to VIO + 0.3 V
−0.3 V to VIO + 0.3 V
−65°C to +150°C
150°C
200°C/W (MSOP-10)
44°C/W (MSOP-10)
215°C
220°C
Stresses above those listed under Absolute Maximum Ratings
may cause permanent damage to the device. This is a stress
rating only; functional operation of the device at these or any
other conditions above those indicated in the operational
section of this specification is not implied. Exposure to absolute
maximum rating conditions for extended periods may affect
device reliability.
ESD 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 this product features
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.
500μA IOL
TO SDO
CL
20pF
1.4V
500μA IOH
Figure 2. Load Circuit for Digital Interface Timing
30% VIO
70% VIO
tDELAY
2V OR VIO – 0.5V1
0.8V OR 0.5V2
tDELAY
2V OR VIO – 0.5V1
0.8V OR 0.5V2
12V IF VIO ABOVE 2.5V, VIO – 0.5V IF VIO BELOW 2.5V.
20.8V IF VIO ABOVE 2.5V, 0.5V IF VIO BELOW 2.5V.
Figure 3. Voltage Levels for Timing
Rev PrC | Page 6 of 23

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AD7982 pdf, datenblatt
AD7982
Preliminary Technical Data
ANALOG INPUT
Figure 14 shows an equivalent circuit of the input structure of
the AD7982.
The two diodes, D1 and D2, provide ESD protection for the
analog inputs IN+ and IN−. Care must be taken to ensure that
the analog input signal never exceeds the supply rails by more
than 0.3 V because this causes these diodes to begin to forward-
bias and start conducting current. These diodes can handle a
forward-biased current of 130 mA maximum. For instance,
these conditions could eventually occur when the input buffer’s
(U1) supplies are different from VDD. In such a case, an input
buffer with a short-circuit, current limitation can be used to
protect the part.
REF
IN+
OR IN–
GND
D1
CPIN
D2
RIN CIN
Figure 14. Equivalent Analog Input Circuit
The analog input structure allows the sampling of the true
differential signal between IN+ and IN−. By using these
differential inputs, signals common to both inputs are rejected.
During the acquisition phase, the impedance of the analog
inputs (IN+ or IN−) can be modeled as a parallel combination
of capacitor, CPIN, and the network formed by the series
connection of RIN and CIN. CPIN is primarily the pin capacitance.
RIN is typically 400 Ω and is a lumped component made up of
some serial resistors and the on resistance of the switches. CIN is
typically 30 pF and is mainly the ADC sampling capacitor.
During the conversion phase, where the switches are opened,
the input impedance is limited to CPIN. RIN and CIN make a 1-
pole, low-pass filter that reduces undesirable aliasing effects and
limits the noise.
When the source impedance of the driving circuit is low, the
AD7982 can be driven directly. Large source impedances
significantly affect the ac performance, especially total
harmonic distortion (THD). The dc performances are less
sensitive to the input impedance. The maximum source
impedance depends on the amount of THD that can be
tolerated. The THD degrades as a function of the source
impedance and the maximum input frequency.
DRIVER AMPLIFIER CHOICE
Although the AD7982 is easy to drive, the driver amplifier
needs to meet the following requirements:
The noise generated by the driver amplifier needs to be
kept as low as possible in order to preserve the SNR and
transition noise performance of the AD7982. The noise
coming from the driver is filtered by the AD7982 analog
input circuit 1-pole, low-pass filter made by RIN and CIN or
by the external filter, if one is used. Because the typical
noise of the AD7982 is 40 μV rms, the SNR degradation
due to the amplifier is
⎜⎛
SNRLOSS
=
20log
40
⎟⎞
402
+
π
2
f3dB (NeN )2
where:
f–3dB is the input bandwidth in MHz of the AD7982
(10MHz) or the cutoff frequency of the input filter, if one is
used.
N is the noise gain of the amplifier (for example, +1 in
buffer configuration).
eN is the equivalent input noise voltage of the op amp, in
nV/√Hz.
For ac applications, the driver should have a THD
performance commensurate with the AD7982.
For multichannel multiplexed applications, the driver
amplifier and the AD7982 analog input circuit must settle
for a full-scale step onto the capacitor array at a 18-bit level
(0.0004%, 4 ppm). In the amplifier’s data sheet, settling at
0.1% to 0.01% is more commonly specified. This could
differ significantly from the settling time at a 18-bit level
and should be verified prior to driver selection.
Table 8. Recommended Driver Amplifiers
Amplifier
Typical Application
ADA4941
Very low noise, low power single to
Differential
ADA4841
Very low noise, small and low power
AD8021
Very low noise and high frequency
AD8022
Low noise and high frequency
OP184
Low power, low noise, and low frequency
AD8655
5 V single-supply, low noise
AD8605, AD8615 5 V single-supply, low power
Rev PrC | Page 12 of 23

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