AD7934-6 Analog Devices, AD7934-6 Datasheet - Page 20

• Manufacturer Part Number: AD7934-6
• Description: 4-Channel, 625 kSPS, 12-Bit Parallel ADC with a Sequencer
• Manufacturer: Analog Devices

Specifications of AD7934-6

• Resolution (bits): 12bit
• # Chan: 4
• Sample Rate: 625kSPS
• Interface: Par
• Analog Input Type: Diff-Uni,SE-Uni
• Ain Range: Uni (Vref),Uni (Vref) x 2
• Adc Architecture: SAR
• Pkg Type: SOP

AD7934-6
The ADC then returns to Channel 0 and starts the sequence
again. The WR input must be kept high to ensure that the control
register is not accidentally overwritten and the sequence inter-
rupted. This pattern continues until the AD7934-6 is written to.
Figure 31 shows the flowchart of the consecutive sequence mode.
REFERENCE
The AD7934-6 can operate with either the on-chip reference or
external reference. The internal reference is selected by setting
the REF bit in the internal control register to 1. A block diagram
of the internal reference circuitry is shown in Figure 32. The
internal reference circuitry includes an on-chip 2.5 V band gap
reference and a reference buffer. When using the internal refer-
ence, the V
a 0.47 μF capacitor. This internal reference not only provides
the reference for the analog-to-digital conversion, but it can also
be used externally in the system. It is recommended that the
reference output is buffered using an external precision op amp
before applying it anywhere in the system.
Alternatively, an external reference can be applied to the
V
is selected by setting the REF bit in the internal control register to
0. The external reference input range is 0.1 V to V
to ensure that when choosing the reference value, the maximum
analog input range (V
order to comply with the maximum ratings of the device. For
example, if operating in differential mode and the reference is
sourced from V
is because the analog input signal range now extends to 2 × V
which exceeds maximum rating conditions. In the pseudo
differential modes, the user must ensure that (V
when using the 0 V to V
when using the 2 × V
In all cases, the specified reference is 2.5 V.
REFIN
/V
REFOUT
Figure 32. Internal Reference Circuit Block Diagram
Figure 31. Consecutive Sequence Mode Flow Chart
REFIN
V
V
REFOUT
REFIN
pin of the AD7934-6. An external reference input
SELECTED FINAL CHANNEL ON ADD1 AND ADD0
CONTINUOUSLY CONVERT ON A CONSECUTIVE
/V
DD
SEQUENCE OF CHANNELS FROM CHANNEL 0
SET UP OPERATING MODE, ANALOG INPUT,
/
UP TO AND INCLUDING THE PREVIOUSLY
, the 0 V to 2 × V
WRITE TO THE CONTROL REGISTER TO
AND OUTPUT CONFIGURATION. SELECT
REFOUT
FINAL CHANNEL (ADD1 AND ADD0) IN
REF
IN MAX
WITH EACH CONVST PULSE.
CONSECUTIVE SEQUENCE.
REF
range.
pin should be decoupled to AGND with
BUFFER
SET SEQ0 = SEQ1 = 1.
) is never greater than V
range, or that (2 × V
POWER ON
ADC
REF
range cannot be used. This
REFERENCE
AD7934-6
REF
REF
DD
. It is important
+ V
+ V
DD
+ 0.3 V, in
IN−
IN−
) ≤ V
) ≤ V
DD
Rev. B | Page 20 of 28
DD
DD
,
The performance of the part with different reference values is
shown in Figure 9, Figure 10, and Figure 11. The value of the
reference sets the analog input span and the common-mode
voltage range. Errors in the reference source result in gain
errors in the AD7934-6 transfer function and add to the
specified full-scale errors on the part.
Table 11 lists suitable voltage references available from Analog
Devices that can be used. Figure 33 shows a typical connection
diagram for an external reference.
Table 11. Examples of Suitable Voltage References
Reference
AD780
ADR421
ADR420
Digital Inputs
The digital inputs applied to the AD7934-6 are not limited by
the maximum ratings that limit the analog inputs. Instead, the
digital inputs applied can go to 7 V. They are not restricted by
the V
Another advantage of the digital inputs not being restricted by
the V
are avoided. If any of these inputs are applied before V
no risk of latch-up as there is on the analog inputs if a signal
greater than 0.3 V is applied prior to V
V
The AD7934-6 also has a V
voltage at which the parallel interface operates. V
ADC to easily interface to 3 V and 5 V processors. For example,
if the AD7934-6 is operated with a V
pin is powered from a 3 V supply, the AD7934-6 has better
dynamic performance with a V
interface to 3 V processors. Care should be taken to ensure
V
Absolute Maximum Ratings section).
V
*ADDITIONAL PINS OMITTED FOR CLARITY.
DD
0.1µF
DRIVE
DRIVE
DD
DD
Input
does not exceed V
+ 0.3 V limit is that the power supply sequencing issues
+ 0.3 V limit that is on the analog inputs.
10nF
Output
Voltage (V)
2.5/3
2.5
2.048
Figure 33. Typical V
0.1µF
NC
DD
NC = NO CONNECT
1
2
3
4
DRIVE
by more than 0.3 V (see the
+V
TEMP
GND
Initial Accuracy
(% maximum)
0.04
0.04
0.05
O/P SELECT
IN
AD780
REF
DD
Connection Diagram
feature. V
of 5 V while still being able to
V
TRIM
OUT
DD
DD
of 5 V, and the V
8
7
6
5
.
2.5V
DRIVE
NC
NC
NC
controls the
Operating
Current (μA)
1000
500
500
DRIVE
AD7934-6*
DD
allows the
, there is
0.1µF
DRIVE
V
REF