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a

AD7827

One Technology Way, P.O. Box 9106, Norwood, MA 02062-9106, U.S.A.

Tel: 781/329-4700

World Wide Web Site: http://www.analog.com

Fax: 781/326-8703

© Analog Devices, Inc., 1998

3 V/5 V, 1 MSPS, 8-Bit, Serial Interface

Sampling ADC

FUNCTIONAL BLOCK DIAGRAM

FEATURES

8-Bit Half-Flash ADC with 420 ns Conversion Time

200 ns Acquisition Time

8-Lead Package

On-Chip Track-and-Hold

On-Chip 2.5 V Reference with 2% Tolerance

Operating Supply Range: 3 V

10% and 5 V

10%

Specifications @ 3 V and 5 V

DSP/Microcontroller Compatible Serial Interface

Automatic Power-Down at End of Conversion

Input Ranges

GENERAL DESCRIPTION

The AD7827 is a high speed, single channel, low power, analog-

to-digital converter with a maximum throughput of 1 MSPS that

operates from a single 3 V or 5 V supply. The AD7827 contains

a track/hold amplifier, an on-chip 2.5 V reference (2% toler-

ance), a 420 ns 8-bit half-flash ADC and a serial interface. The

serial interface is compatible with the serial interfaces of most

DSPs (Digital Signal Processors). The throughput rate of the

AD7827 is dependent on the clock speed of the DSP serial

interface.

The AD7827 combines the Convert Start and Power Down

signals at one pin, i.e., the

CONVST pin. This allows a unique

automatic power-down at the end of a conversion to be imple-

mented. The logic level on the

CONVST pin is sampled at the

end of a conversion and, depending on its state, the AD7827

powers down.

The AD7827 has one single-ended analog input with an input

5 V, the input range is 0 V to 2.5 V.

The parts are available in a small, 8-lead, 0.3" wide, plastic

dual-in-line package (DIP) and an 8-lead, small outline IC

(SOIC).

PRODUCT HIGHLIGHTS

1. Fast Conversion Time

The AD7827 has a conversion time of 420 ns. Faster conver-

sion times maximize the DSP processing time in a real time

system.

2. Built-In Track-and-Hold

The analog input signal is held and a new conversion is initi-

ated on the falling edge of the

CONVST signal. The CONVST

signal allows the sampling instant to be exactly controlled.

This feature is a requirement in many DSP applications.

3. Automatic Power-Down

The

CONVST signal is sampled approximately 100 ns after

the end of conversion and depending on its state the AD7827

is powered down.

4. An easy to use, fast serial interface allows direct interfacing to

most popular DSPs with no external circuitry.

BUF

T/H

2.5V

REF

8-BIT

HALF-FLASH

ADC

SERIAL

PORT

CONTROL

LOGIC

DETECT

RFS

SCLK

CONVST

GND

COMP

AD7827