REV. B

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a

AD7822/AD7825/AD7829

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

Tel: 781/329-4700

www.analog.com

Fax: 781/326-8703

© Analog Devices, Inc., 2001

3 V/5 V, 2 MSPS, 8-Bit, 1-, 4-, 8-Channel

Sampling ADCs

FUNCTIONAL BLOCK DIAGRAM

CONVST

8-BIT

HALF

FLASH

ADC

PARALLEL

PORT

EOC

RD

CS

AGND

A0* A1* A2*

COMP

PD*

2.5V

REF

CONTROL

LOGIC

DGND

INPUT

MUX

T/H

*A0, A1

*A2

*

PD

AD7825/AD7829

AD7829

AD7822/AD7825

AD7825/AD7829

AD7829

BUF

DB0

DB7

FEATURES

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

1, 4 and 8 Single-Ended Analog Input Channels

Available with Input Offset Adjust

On-Chip Track-and-Hold

SNR Performance Given for Input Frequencies Up to

10 MHz

On-Chip Reference (2.5 V)

Automatic Power-Down at the End of Conversion

Wide Operating Supply Range

3 V

10% and 5 V

10%

Input Ranges

10%

10%

Flexible Parallel Interface with EOC Pulse to Allow

Stand-Alone Operation

APPLICATIONS

Data Acquisition Systems, DSP Front Ends

Disk Drives

Mobile Communication Systems, Subsampling

Applications

GENERAL DESCRIPTION

The AD7822, AD7825, and AD7829 are high speed, 1-, 4-, and

8-channel, microprocessor-compatible, 8-bit analog-to-digital

converters with a maximum throughput of 2 MSPS. The AD7822,

AD7825, and AD7829 contain an on-chip reference of 2.5 V

(2% tolerance), a track/hold amplifier, a 420 ns 8-bit half-flash

ADC and a high speed parallel interface. The converters can

operate from a single 3 V

± 10% and 5 V ± 10% supply.

The AD7822, AD7825, and AD7829 combine the convert start

and power-down functions at one pin, i.e., the CONVST pin.

This allows a unique automatic power-down at the end of a

conversion to be implemented. The logic level on the CONVST

pin is sampled after the end of a conversion when an EOC (End

of Conversion) signal goes high, and if it is logic low at that

point, the ADC is powered down. The AD7822 and AD7825

also have a separate power-down pin. (See Operating Modes

section of the data sheet.)

The parallel interface is designed to allow easy interfacing to

microprocessors and DSPs. Using only address decoding logic,

the parts are easily mapped into the microprocessor address

space. The EOC pulse allows the ADCs to be used in a stand-

alone manner. (See Parallel Interface section of the data sheet.)

The AD7822 and AD7825 are available in a 20-/24-lead 0.3"

wide, plastic dual-in-line package (DIP), a 20-/24-lead small out-

line IC (SOIC) and a 20-/24-lead thin shrink small outline package

(TSSOP). The AD7829 is available in a 28-lead 0.6" wide, plastic

dual-in-line package (DIP), a 28-lead small outline IC (SOIC) and

in a 28-lead thin shrink small outline package (TSSOP).

PRODUCT HIGHLIGHTS

1. Fast Conversion Time

The AD7822, AD7825, and AD7829 have a conversion time

of 420 ns. Faster conversion times maximize the DSP pro-

cessing time in a real-time system.

2. Analog Input Span Adjustment

feature can reduce the requirements of single-supply op amps

and take into account any system offsets.

3. FPBW (Full Power Bandwidth) of Track-and-Hold

The track-and-hold amplifier has an excellent high-frequency

performance. The AD7822, AD7825, and AD7829 are

capable of converting full-scale input signals up to a fre-

quency of 10 MHz. This makes the parts ideally suited to

subsampling applications.

4. Channel Selection

Channel selection is made without the necessity of writing to

the part.