AD7923 Analog Devices, AD7923 Datasheet - Page 16

• Manufacturer Part Number: AD7923
• Description: 4-Channel 200 kSPS, 12-Bit A/D Converter with Sequencer in 16-Lead TSSOP
• Manufacturer: Analog Devices

Specifications of AD7923

• Resolution (bits): 12bit
• # Chan: 4
• Sample Rate: 200kSPS
• Interface: Ser,SPI
• Analog Input Type: SE-Uni
• Ain Range: Uni (Vref),Uni (Vref) x 2
• Adc Architecture: SAR
• Pkg Type: SOP

AD7923
TYPICAL CONNECTION DIAGRAM
Figure 19 shows a typical connection diagram for the AD7923.
In this setup the AGND pin is connected to the analog ground
plane of the system. In Figure 19, REF
decoupled 2.5 V supply from a reference source, the AD780, to
provide an analog input range of 0 V to 2.5 V (if the range bit is
1) or 0 V to 5 V (if the range bit is 0). Although the AD7923 is
connected to AV
3 V microprocessor. The V
to the same 3 V supply of the microprocessor to allow a 3 V
logic interface (see the Digital Inputs section). The conversion
result is output in a 16-bit word. This 16-bit data stream
consists of two leading 0s, two address bits indicating which
channel the conversion result corresponds to, followed by the
12 bits of conversion data. For applications where power
consumption is a concern, the power-down modes should be
used between conversions or bursts of several conversions to
improve power performance. See the Modes of Operation
section.
0V TO REF
Analog Input Selection
Any one of four analog input channels can be selected for
conversion by programming the multiplexer with Address Bits
ADD1 and ADD0 in the control register. The channel
configurations are shown in Table 7.
The AD7923 can also be configured to automatically cycle
through selected channels. The sequencer feature is accessed via
the SEQ1 and SEQ0 bits in the control register (see Table 9).
The AD7923 can be programmed to continuously convert on a
number of consecutive channels in ascending order from
Channel 0 to a selected final channel as determined by Channel
Address Bits ADD1 and ADD0. This is possible if the SEQ1 and
SEQ0 bits are set to 1, 1. The next serial transfer then acts on
the sequence programmed by executing a conversion on
Channel 0. The next serial transfer results in a conversion on
Channel 1, and so on, until the channel selected via Address
Bits ADD1 and ADD0 is reached. It is not necessary to write to
NOTES
1. ALL UNUSED INPUT CHANNELS MUST BE CONNECTED TO AGND.
0.1μF
IN
AGND
V
V
IN
IN
0
3
•
•
Figure 19. Typical Connection Diagram
DD
REF
AV
DD
of 5 V, the serial interface is connected to a
IN
0.1μF
AD7923
AD780
2.5V
DRIVE
10μF
pin of the AD7923 is connected
V
DRIVE
DOUT
SCLK
0.1μF
DIN
IN
CS
5V
SUPPLY
is connected to a
INTERFACE
SERIAL
10μF
SUPPLY
μC/μP
3V
Rev. C | Page 16 of 24
the control register again once a sequencer operation has been
initiated. The write bit must be set to 0 or the DIN line must be
set low to ensure that the control register is not accidentally
overwritten or the sequence operation is interrupted. If the
control register is written to at any time during the sequence,
the user must ensure that the SEQ1 and SEQ0 bits are set to 1, 0
to avoid interrupting the automatic conversion sequence. This
pattern continues until the AD7923 is written to and the SEQ1
and SEQ0 bits are configured with any bit combination except
1, 0, resulting in the termination of the sequence. If uninter-
rupted, however (write bit = 0, or write bit = 1 and SEQ1 and
SEQ0 bits are set to 1, 0), then upon completion of the
sequence, the AD7923 sequencer returns to Channel 0 and
commences the sequence again.
Regardless of which channel selection method is used, the
16-bit word output from the AD7923 during each conversion
always contains two leading 0s, and two channel address bits
that the conversion result corresponds to, followed by the 12-bit
conversion result. (see the Serial Interface section).
Digital Inputs
The digital inputs applied to the AD7923 are not limited by the
maximum ratings that limit the analog inputs. Instead, the
digital inputs applied can go to 7 V and are not restricted by the
AV
Another advantage of SCLK, DIN, and CS not being restricted
by the AV
sequencing issues are avoided. If CS , DIN, or SCLK are applied
before AV
analog inputs if a signal greater than 0.3 V were applied prior to
AV
V
The AD7923 also has the V
voltage at which the serial interface operates. V
ADC to easily interface to both 3 V and 5 V processors. For
example, if the AD7923 were operated with an AV
V
has a larger dynamic range with an AV
able to interface to 3 V processors. Care should be taken to
ensure that V
(see the Absolute Maximum Ratings section).
Reference
An external reference source should be used to supply the 2.5 V
reference to the AD7923. Errors in the reference source result in
gain errors in the AD7923 transfer function and add to the
specified full-scale errors of the part. A capacitor of at least
0.1 μF should be placed on the REF
sources for the AD7923 include the AD780, REF 192, and the
AD1582.
DRIVE
DRIVE
DD
DD
.
+ 0.3 V limit as on the analog inputs.
pin could be powered from a 3 V supply. The AD7923
DD
DD
, there is no risk of latchup as there would be on the
+ 0.3 V limit is that possible power supply
DRIVE
does not exceed AV
DRIVE
feature. V
IN
pin. Suitable reference
DD
DD
by more than 0.3 V
of 5 V while still being
DRIVE
controls the
DRIVE
DD
allows the
of 5 V, the