3 V/5 V, 1 MSPS, 8-Bit, Serial Interface
Sampling ADC
a
AD7827
FEATURES
FUNCTIO NAL BLO CK D IAGRAM
8-Bit Half-Flash ADC w ith 420 ns Conversion Tim e
200 ns Acquisition Tim e
V
/V
V
DD
REFIN REFOUT
GND
8-Lead Package
On-Chip Track-and-Hold
2.5V
REF
V
AD7827
DD
DETECT
On-Chip 2.5 V Reference w ith 2% Tolerance
Operating Supply Range: 3 V ؎ 10% and 5 V ؎ 10%
Specifications @ 3 V and 5 V
DSP/ Microcontroller Com patible Serial Interface
Autom atic Pow er-Dow n at End of Conversion
Input Ranges
CONTROL
LOGIC
CONVST
COMP
BUF
SCLK
8-BIT
SERIAL
PORT
V
T/H
IN
HALF-FLASH
ADC
D
OUT
0 V to 2 V, VDD = 3 V
RFS
0 V to 2.5 V, VDD = 5 V
GENERAL D ESCRIP TIO N
P RO D UCT H IGH LIGH TS
T he 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. T he 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. T he
serial interface is compatible with the serial interfaces of most
DSPs (Digital Signal Processors). T he throughput rate of the
AD7827 is dependent on the clock speed of the DSP serial
interface.
1. Fast Conversion T ime
T he 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 T rack-and-Hold
T he 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.
T his feature is a requirement in many DSP applications.
T he AD7827 combines the Convert Start and Power Down
signals at one pin, i.e., the CONVST pin. T his allows a unique
automatic power-down at the end of a conversion to be imple-
mented. T he logic level on the CONVST pin is sampled at the
end of a conversion and, depending on its state, the AD7827
powers down.
3. Automatic Power-Down
T he 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.
T he 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.
T he 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).
REV. 0
Inform ation furnished by Analog Devices is believed to be accurate and
reliable. However, no responsibility is assum ed by Analog Devices for its
use, nor for any infringem ents of patents or other rights of third parties
which m ay result from its use. No license is granted by im plication or
otherwise under any patent or patent rights of Analog Devices.
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© Analog Devices, Inc., 1998