3 V/5 V, 2 MSPS, 8-Bit, 1-/4-/8-Channel
Sampling ADCs
AD7822/AD7825/AD7829
FEATURES
VDD
CONVST EOC A01 A11 A22 PD3
CONTROL
LOGIC
VIN1
VIN24
VIN34
VIN44
VIN55
VIN65
VIN75
VIN85
INPUT
MUX
1A0, A1
2A2
3PD
4V
IN2 TO VIN4
5V
IN5 TO VIN8
Data acquisition systems, DSP front ends
Disk drives
Mobile communication systems, subsampling
applications
2.5V
REF
BUF
T/H
VMID
APPLICATIONS
COMP
8-BIT
HALF
FLASH
ADC
DGND
AGND
PARALLEL
PORT
VREF IN/OUT
DB7
DB0
CS RD
AD7825/AD7829
AD7829
AD7822/AD7825
AD7825/AD7829
AD7829
01321-001
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
FUNCTIONAL BLOCK DIAGRAM
Figure 1.
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 halfflash ADC; and a high speed parallel interface. The converters
can operate from a single 3 V ± 10% and 5 V ± 10% supply.
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.
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).
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.
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 standalone manner (see the Parallel Interface section.)
PRODUCT HIGHLIGHTS
Rev. C
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