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REV. A

AD7908/AD7918/AD7928

8-Channel, 1 MSPS, 8-/10-/12-Bit ADCs

with Sequencer in 20-Lead TSSOP

FUNCTIONAL BLOCK DIAGRAM

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T/H

I/P

MUX

SEQUENCER

CONTROL LOGIC

8-/10-/12-BIT

SUCCESSIVE

APPROXIMATION

ADC

GND

SCLK

DOUT

DIN

CS

AD7908/AD7918/AD7928

FEATURES

Fast Throughput Rate: 1 MSPS

Low Power:

6.0 mW Max at 1 MSPS with 3 V Supply

13.5 mW Max at 1 MSPS with 5 V Supply

8 (Single-Ended) Inputs with Sequencer

Wide Input Bandwidth:

AD7928, 70 dB Min SINAD at 50 kHz Input Frequency

Flexible Power/Serial Clock Speed Management

No Pipeline Delays

MICROWIRE™/DSP Compatible

Shutdown Mode: 0.5 A Max

20-Lead TSSOP Package

GENERAL DESCRIPTION

The AD7908/AD7918/AD7928 are, respectively, 8-bit, 10-bit,

and 12-bit, high speed, low power, 8-channel, successive

approximation ADCs. The parts operate from a single 2.7 V

to 5.25 V power supply and feature throughput rates up to

1MSPS. The parts contain a low noise, wide bandwidth track-

and-hold amplifier that can handle input frequencies in excess

of 8 MHz.

The conversion process and data acquisition are controlled using

CS and the serial clock signal, allowing the device to easily inter-

face with microprocessors or DSPs. The input signal is sampled

on the falling edge of

CS and conversion is also initiated at this

point. There are no pipeline delays associated with the part.

The AD7908/AD7918/AD7928 use advanced design techniques to

achieve very low power dissipation at maximum throughput rates.

At maximum throughput rates, the AD7908/AD7918/AD7928

consume 2 mA maximum with 3 V supplies; with 5 V supplies, the

current consumption is 2.7 mA maximum.

Through the configuration of the Control Register, the analog

2

put coding. The AD7908/AD7918/AD7928 each feature eight

single-ended analog inputs with a channel sequencer to allow a

preprogrammed selection of channels to be converted sequentially.

The conversion time for the AD7908/AD7918/AD7928 is deter-

mined by the SCLK frequency, which is also used as the master

clock to control the conversion.

PRODUCT HIGHLIGHTS

1. High Throughput with Low Power Consumption.

The AD7908/AD7918/AD7928 offer up to 1 MSPS throughput

rates. At the maximum throughput rate with 3 V supplies, the

AD7908/AD7918/AD7928 dissipate just 6 mW of power

maximum.

2. Eight Single-Ended Inputs with a Channel Sequencer.

A sequence of channels can be selected, through which the

ADC will cycle and convert on.

The AD7908/AD7918/AD7928 operate from a single 2.7 V to

to connect directly to either 3 V or 5 V processor systems

4. Flexible Power/Serial Clock Speed Management.

The conversion rate is determined by the serial clock, allowing

the conversion time to be reduced through the serial clock

speed increase. The parts also feature various shutdown

modes to maximize power efficiency at lower throughput rates.

Current consumption is 0.5 µA max when in full shutdown.

5. No Pipeline Delay.

The parts feature a standard successive approximation ADC

with accurate control of the sampling instant via a

CS input

and once off conversion control.