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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, respectively, 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 specifications, 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-tonoise 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
07730-001
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 r.