12-Bit, 100 kHz, Sampling ADCs

AD7870/AD7875/AD7876

Rev. C

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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

FUNCTIONAL BLOCK DIAGRAM

REF OUT

INPUT

SCALING

12-BIT

DAC

PARALLEL

AND SERIAL

INTERFACE

AD7870/AD7875/

AD7876

CONTROL LOGIC

CLOCK

3V

REFERENCE

SAR +

COUNTER

COMP

TRACK-AND-HOLD

DGND

DB11

DB0

CS

RD BUSY/INT

AGND

CLK

CONVST

12/8/CLK

Figure 1.

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.

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.