AD7822 Datasheet, PDF (1/20 Pages) Analog Devices – 3 V/5 V, 2 MSPS, 8-Bit, 1-, 4-, 8-Channel Sampling ADCs

a 3 V/5 V, 2 MSPS, 8-Bit, 1-, 4-, 8-Channel
Sampling ADCs
AD7822/AD7825/AD7829
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
0 V to 2 V p-p, V_DD = 3 V ؎ 10%
0 V to 2.5 V p-p, V_DD = 5 V ؎ 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
FUNCTIONAL BLOCK DIAGRAM
CONVST EOC A0* A1* A2* PD*
V_DD
CONTROL
LOGIC
COMP
2.5V
REF
V_IN1
V_IN2*
V_IN3*
V_IN4*
V_IN5*
V_IN6*
V_IN7*
V_IN8*
INPUT
MUX
T/H
8-BIT
HALF
FLASH
ADC
V_{MID AGND DGND}
*A0, A1
*A2
*PD
*V_IN2 TO V_IN4
*V_IN4 TO V_IN8
AD7825/AD7829
AD7829
AD7822/AD7825
AD7825/AD7829
AD7829
BUF
PARALLEL
PORT
CS RD
VREF_{IN / OUT}
DB7
DB0
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
The V_MID pin allows the user to offset the input span. This
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.
REV. B
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© Analog Devices, Inc., 2001