AD7827 Analog Devices Data Handbook/Manual

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

Sampling ADC AD7827 FUNCTIONAL BLOCK DIAGRAMFEATURES

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

GNDVDDVREFIN/VREFOUT

200 ns Acquisition Time 8-Lead Package

2.5V VDD AD7827

On-Chip Track-and-Hold REF

DETECT

On-Chip 2.5 V Reference with 2% Tolerance

CONTROL

Operating Supply Range: 3 V 6 10% and 5 V 6 10% COMP CONVST

BUF LOGIC

Specifications @ 3 V and 5 V DSP/Microcontroller Compatible Serial Interface

Automatic Power-Down at End of Conversion

8-BIT

VIN T/H SERIAL

Input Ranges HALF-FLASH DOUT

0 V to 2 V, VDD = 3 V

0 V to 2.5 V, VDD = 5 V

GENERAL DESCRIPTION PRODUCT HIGHLIGHTS The AD7827 is a high speed, single channel, low power, analog- 1. Fast Conversion Time to-digital converter with a maximum throughput of 1 MSPS that The AD7827 has a conversion time of 420 ns. Faster conver- operates from a single 3 V or 5 V supply. The AD7827 contains sion times maximize the DSP processing time in a real time a track/hold amplifier, an on-chip 2.5 V reference (2% toler- system. ance), a 420 ns 8-bit half-flash ADC and a serial interface. The

2. Built-In Track-and-Hold

serial interface is compatible with the serial interfaces of most

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

DSPs (Digital Signal Processors). The throughput rate of the www.BDTIC.c m/ADI

ated on the falling edge of the CONVST signal. The CONVST

AD7827 is dependent on the clock speed of the DSP serial

signal allows the sampling instant to be exactly controlled.

interface.

This feature is a requirement in many DSP applications.

The AD7827 combines the Convert Start and Power Down

3. Automatic Power-Down

signals at one pin, i.e., the CONVST pin. This allows a unique

The CONVST signal is sampled approximately 100 ns after

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

the end of conversion and depending on its state the AD7827

mented. The logic level on the CONVST pin is sampled at the

is powered down.

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

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

powers down.

most popular DSPs with no external circuitry.

The AD7827 has one single-ended analog input with an input span determined by the supply voltage. With a VDD of 3 V, the input range of the AD7827 is 0 V to 2 V and with VDD equal to 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).

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