AD7822_15 Datasheet, PDF (1/28 Pages) Analog Devices – 3 V/5 V, 2 MSPS, 8-Bit, 1-/4-/8-Channel Sampling ADCs

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
One, four, and eight 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, VDD = 3 V ± 10%
0 V to 2.5 V p-p, VDD = 5 V ± 10%
Flexible parallel interface with EOC pulse to allow
standalone operation
APPLICATIONS
Data acquisition systems, DSP front ends
Disk drives
Mobile communication systems, subsampling
applications
GENERAL DESCRIPTION
The AD7822/AD7825/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/AD7829 contain an on-chip reference of 2.5 V
(2% tolerance); a track-and-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/AD7829 combine the convert start and
power-down functions at one pin, that is, 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. 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 the Operating Modes section).
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 the Parallel Interface section.)
Rev. C
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FUNCTIONAL BLOCK DIAGRAM
CONVST EOC A0¹ A1¹ A2² PD³
V_DD
CONTROL
LOGIC
COMP
2.5V
REF
V_IN1
V_IN24
V_IN34
V_IN44
V_IN55
V_IN65
V_IN75
V_IN85
INPUT
MUX
T/H
8-BIT
HALF
FLASH
ADC
BUF
PARALLEL
PORT
V_{MID AGND DGND}
CS RD
1_{A0, A1}
2_A2
3_PD
4_{VIN2 TO VIN4}
5_{VIN5 TO VIN8}
AD7825/AD7829
AD7829
AD7822/AD7825
AD7825/AD7829
AD7829
Figure 1.
V_{REF IN/OUT}
DB7
DB0
The AD7822 and AD7825 are available in 20-lead and 24-lead,
0.3" wide, plastic dual in-line packages (PDIP); 20-lead and
24-lead standard small outline packages (SOIC); and 20-lead
and 24-lead thin shrink small outline packages (TSSOP). The
AD7829 is available in a 28-lead, 0.6" wide PDIP; a 28-lead
SOIC; and a 28-lead TSSOP.
PRODUCT HIGHLIGHTS
1. Fast Conversion Time. The AD7822/AD7825/AD7829
have a conversion time of 420 ns. Faster conversion times
maximize the DSP processing time in a real-time system.
2. Analog Input Span Adjustment. The VMID 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/AD7829
are capable of converting full-scale input signals up to a
frequency 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.
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