AD7827 Datasheet, PDF (1/12 Pages) Analog Devices – 3 V/5 V, 1 MSPS, 8-Bit, Serial Interface Sampling ADC

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3 V/5 V, 1 MSPS, 8-Bit, Serial Interface
Sampling ADC
AD7827
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
0 V to 2 V, V_DD = 3 V
0 V to 2.5 V, V_DD = 5 V
FUNCTIONAL BLOCK DIAGRAM
V_REFIN/V_REFOUT
V_DD
GND
2.5V
REF
BUF
V_DD
DETECT
COMP
AD7827
CONTROL
LOGIC
CONVST
8-BIT
V_IN
T/H
HALF-FLASH
ADC
SERIAL
PORT
SCLK
D_OUT
RFS
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
span determined by the supply voltage. With a V_DD of 3 V, the
input range of the AD7827 is 0 V to 2 V and with V_DD 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).
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.
REV. 0
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