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PDF AD7875 Data sheet ( Hoja de datos )
| Número de pieza | AD7875 | |
| Descripción | LC2MOS Complete/ 12-Bit/ 100 kHz/ Sampling ADCs | |
| Fabricantes | Analog Devices | |
| Logotipo |  |
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Hay una vista previa y un enlace de descarga de AD7875 (archivo pdf) en la parte inferior de esta página. Total 28 Páginas | ||
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FEATURES
Complete monolithic 12-bit ADCs with
2 μs track-and-hold amplifier
8 μs ADC
On-chip reference
Laser-trimmed clock
Parallel, byte, and serial digital interface
72 dB SNR at 10 kHz input frequency
(AD7870, AD7875)
57 ns data access time
Low power: −60 mW typical
Variety of input ranges
±3 V for AD7870
0 V to +5 V for AD7875
±10 V for AD7876
GENERAL DESCRIPTION
The AD7870/AD7875/AD7876 are fast, complete, 12-bit
analog-to-digital converters (ADCs). These converters consist
of a track-and-hold amplifier, an 8 μs successive approximation
ADC, a 3 V buried Zener reference, and versatile interface logic.
The ADCs feature a self-contained internal clock which is laser
trimmed to guarantee accurate control of conversion time. No
external clock timing components are required; the on-chip
clock may be overridden by an external clock if required.
The parts offer a choice of three data output formats: a single,
parallel, 12-bit word; two 8-bit bytes or serial data. Fast bus
access times and standard control inputs ensure easy interfacing
to modern microprocessors and digital signal processors.
All parts operate from ±5 V power supplies. The AD7870 and
AD7876 accept input signal ranges of ±3 V and ±10 V, respec-
tively, while the AD7875 accepts a unipolar 0 V to +5 V input
range. The parts can convert full power signals up to 50 kHz.
The AD7870/AD7875/AD7876 feature dc accuracy specifica-
tions, such as linearity, full-scale and offset error. In addition,
the AD7870 and AD7875 are fully specified for dynamic
performance parameters including distortion and signal-to-
noise ratio.
LC2MOS Complete,
12-Bit, 100 kHz, Sampling ADCs
AD7870/AD7875/AD7876
FUNCTIONAL BLOCK DIAGRAM
AGND
REF OUT
VIN
VDD
AD7870/AD7875/
INPUT
AD7876
SCALING
TRACK-AND-HOLD
3V
REFERENCE
12-BIT
DAC
COMP
CLK
12/8/CLK
CONVST
CLOCK
CONTROL LOGIC
PARALLEL
AND SERIAL
INTERFACE
SAR +
COUNTER
CS RD BUSY/INT DB11 DB0
Figure 1.
DGND VSS
The parts are available in a 24-pin, 0.3 inch-wide, plastic or
hermetic dual-in-line package (DIP). The AD7870 and AD7875
are available in a 28-pin plastic leaded chip carrier (PLCC),
while the AD7876 is available and in a 24-pin small outline
(SOIC) package.
PRODUCT HIGHLIGHTS
1. Complete 12-bit ADC on a chip.
The AD7870/AD7875/AD7876 provide all the functions
necessary for analog-to-digital conversion and combine a
12-bit ADC with internal clock, track-and-hold amplifier
and reference on a single chip.
2. Dynamic specifications for DSP users.
The AD7870 and AD7875 are fully specified and tested for
ac parameters, including signal-to-noise ratio, harmonic
distortion and intermodulation distortion.
3. Fast microprocessor interface.
Data access times of 57 ns make the parts compatible with
modern 8-bit and 16-bit microprocessors and digital signal
processors. Key digital timing parameters are tested and
guaranteed over the full operating temperature range.
Rev. C
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.
Trademarksandregisteredtrademarksarethepropertyoftheirrespectiveowners.
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 ©1997–2009 Analog Devices, Inc. All rights reserved.
1 page  
AD7870/AD7875/AD7876
Parameter
ANALOG INPUT
AD7875 Input Voltage Range
AD7875 Input Current
AD7876 Input Voltage Range
AD7876 Input Current
REFERENCE OUTPUT
REF OUT @ +25°C
REF OUT Tempco
Reference Load Sensitivity
(ΔREF OUT/ΔI)
AD7875/AD78761
K, B L, C T
0 to +5
500
±10
±600
0 to +5
500
±10
±600
0 to +5
500
±10
±600
2.99 2.99 2.99
3.01 3.01 3.01
±60 ±35 ±60
−1 −1 −1
LOGIC INPUTS
Input High Voltage, VINH
Input Low Voltage, VINL
Input Current, IIN
Input Current (12/8/CLK Input Only)
Input Capacitance, CIN5
LOGIC OUTPUTS
Output High Voltage, VOH
Output Low Voltage, VOL
DB11–DB0
Floating-State Leakage Current
Floating-State Output
Capacitance5
CONVERSION TIME
External Clock (fCLK = 2.5 MHz)
Internal Clock
2.4
0.8
±10
±10
10
4.0
0.4
10
15
8
6.5/9
2.4
0.8
±10
±10
10
4.0
0.4
10
15
8
6.5/9
2.4
0.8
±10
±10
10
4.0
0.4
10
15
8
6.5/9
POWER REQUIREMENTS
As per AD7870
Units
Test Conditions/Comments
V
μA max
V
μA max
V min
V max
ppm/°C max
mV max
Typical tempco Is ±20 ppm/°C
Reference load current change (0 μA to 500 μA).
Reference load should not be changed during
conversion.
V min
V max
μA max
μA max
pF max
VDD = 5 V ± 5%
VDD = 5 V ± 5%
VIN = 0 V to VDD
VIN = VSS to VDD
V min
V max
μA max
pF max
ISOURCE = 40 mA
ISINK = 1.6 mA
μs max
μs min/μs
max
Refer to the power requirements in Table 1.
1 For the AD7875, the temperature range for the K and L versions is from 0°C to +70°C; for the B and C versions is−40°C to +85°C; and for the T version is −55°C to
+125°C. For the AD7876, the temperature range for the B and C versions is from −40°C to +85°C and for the T version is−55°C to +125°C.
2 Includes internal reference error and is calculated after unipolar offset error (AD7875) or bipolar zero error (AD7876) has been adjusted out. Full-scale error refers to
both positive and negative full-scale error for the AD7876.
3 Dynamic performance parameters are not tested on the AD7876, but these are typically the same as for the AD7875.
4 SNR calculation includes distortion and noise components.
5 Sample tested @ +25°C to ensure compliance.
Rev. C | Page 5 of 28
5 Page 
CONVERTER DETAILS
The AD7870/AD7875/AD7876 is a complete 12-bit ADC,
requiring no external components apart from power supply
decoupling capacitors. It is comprised of a 12-bit successive
approximation ADC based on a fast settling voltage output
DAC, a high speed comparator and SAR, a track-and-hold
amplifier, a 3 V buried Zener reference, a clock oscillator,
and control logic.
INTERNAL REFERENCE
The AD7870/AD7875/AD7876 have on-chip temperature
compensated buried Zener reference that is factory trimmed
to 3 V ± 10 mV. Internally it provides both the DAC reference
and the dc bias required for bipolar operation (AD7870 and
AD7876). The reference output is available (REF OUT) and
capable of providing up to 500 μA to an external load.
The maximum recommended capacitance on REF OUT for
normal operation is 50 pF. If the reference is required for use
external to the ADC, it should be decoupled with a 200 Ω
resistor in series with a parallel combination of a 10 μF
tantalum capacitor and a 0.1 μF ceramic capacitor. These
decoupling components are required to remove voltage
spikes caused by the ADC’s internal operation.
VDD AD7870/AD7875/AD7876
TEMPERATURE
COMPENSATION
VSS
REF OUT
Figure 6. Reference Circuit
The reference output voltage is 3 V. For applications using the
AD7875 or AD7876, a 5 V or 10 V reference may be required.
Figure 7 shows how to scale the 3 V REF OUT voltage to
provide either a 5 V or 10 V external reference.
AD7870/AD7875/AD7876
INTERNAL 3V
REFERENCE
REF OUT
VOUT = 5V (10V)
15kΩ
(3.9kΩ)
10kΩ
(9.1kΩ)
Figure 7. Generating a 5 V or 10 V Reference
AD7870/AD7875/AD7876
TRACK-AND-HOLD AMPLIFIER
The track-and-hold amplifier on the analog input of the
AD7870/AD7875/AD7876 allows the ADC to accurately
convert input frequencies to 12-bit accuracy. The input
bandwidth of the track-and-hold amplifier is much greater
than the Nyquist rate of the ADC even when the ADC is
operated at its maximum throughput rate. The 0.1 dB cutoff
frequency occurs typically at 500 kHz. The track-and-hold
amplifier acquires an input signal to 12-bit accuracy in less than
2 μs. The overall throughput rate is equal to the conversion time
plus the track-and-hold amplifier acquisition time. For a 2.5 MHz
input clock the throughput rate is 10 μs max.
The operation of the track-and-hold is essentially transparent
to the user. The track-and-hold amplifier goes from its tracking
mode to its hold mode at the start of conversion.
If the CONVST input is used to start conversion then the track
to hold transition occurs on the rising edge of CONVST. If CS
starts conversion, this transition occurs on the falling edge of CS.
ANALOG INPUT
The three parts differ from each other in the analog input
voltage range that they can handle. The AD7870 accepts ±3 V
input signals, the AD7876 accepts a ±10 V input range, while
the input range for the AD7875 is 0 V to +5 V.
Figure 8 shows the AD7870 analog input. The analog input
range is ±3 V into an input resistance of typically 15 kΩ. The
designed code transitions occur midway between successive
integer LSB values (that is, 1/2 LSB, 3/2 LSBs, 5/2 LSBs . . .
FS–3/2 LSBs). The output code is twos complement binary with
1 LSB = FS/4096 = 6 V/4096 = 1.46 mV. The ideal input/output
transfer function is shown in Figure 11.
AD7870
TRACK-AND-HOLD
AMPLIFIER
R TO INTERNAL
COMPARATOR
R
TO INTERNAL
3V REFERENCE
Figure 8. AD7970 Analog Input
The AD7876 analog input structure is shown in Figure 9. The
analog input range is ±10 V into an input resistance of typically
33 kΩ. As before, the designed code transitions occur midway
between successive integer LSB values. The output code is twos
complement with 1 LSB = FS/4096 = 20 V/4096 = 4.88 mV. The
ideal input/output transfer function is shown in Figure 11.
Rev. C | Page 11 of 28
11 Page | ||
| Páginas | Total 28 Páginas | |
| PDF Descargar | [ Datasheet AD7875.PDF ] | |
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