AD7607 Analog Devices, AD7607 Datasheet - Page 21

• Manufacturer Part Number: AD7607
• Description: 8-Channel DAS with 14-Bit, Bipolar, Simultaneous Sampling ADC
• Manufacturer: Analog Devices

Specifications of AD7607

• Resolution (bits): 14bit
• # Chan: 8
• Sample Rate: 200kSPS
• Interface: Par,Ser,SPI
• Analog Input Type: SE-Bip
• Ain Range: Bip 10V,Bip 5.0V
• Adc Architecture: SAR
• Pkg Type: QFP

Data Sheet
INTERNAL/EXTERNAL REFERENCE
The AD7607 contains an on-chip 2.5 V bandgap reference. The
REFIN/REFOUT pin allows access to the 2.5 V reference that
generates the on-chip 4.5 V reference internally, or it allows
an external reference of 2.5 V to be applied to the AD7607. An
externally applied reference of 2.5 V is also gained up to 4.5 V, using
the internal buffer. This 4.5 V buffered reference is the reference
used by the SAR ADC.
The REF SELECT pin is a logic input pin that allows the user to
select between the internal reference or an external reference.
If this pin is set to logic high, the internal reference is selected
and enabled. If this pin is set to logic low, the internal reference
is disabled and an external reference voltage must be applied
to the REFIN/REFOUT pin. The internal reference buffer is
always enabled. After a reset, the AD7607 operates in the reference
mode selected by the REF SELECT pin. Decoupling is required
on the REFIN/REFOUT pin for both the internal and external
reference options. A 10 μF ceramic capacitor is required on the
REFIN/REFOUT pin.
The AD7607 contains a reference buffer configured to gain the
REF voltage up to ~4.5 V, as shown in Figure 36. The REFCAPA
and REFCAPB pins must be shorted together externally, and
a ceramic capacitor of 10 μF applied to REFGND, to ensure that
the reference buffer is in closed-loop operation. The reference
voltage available at the REFIN/REFOUT pin is 2.5 V.
When the AD7607 is configured in external reference mode,
the REFIN/REFOUT pin is a high input impedance pin. For
applications using multiple AD7607 devices, the following
configurations are recommended, depending on the application
requirements.
External Reference Mode
One ADR421 external reference can be used to drive the
REFIN/REFOUT pins of all AD7607 devices (see Figure 37).
In this configuration, each REFIN/REFOUT pin of the AD7607
should be decoupled with a 100 nF decoupling capacitor.
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Internal Reference Mode
One AD7607 device, configured to operate in the internal
reference mode, can be used to drive the remaining AD7607
devices, which are configured to operate in external reference
mode (see Figure 38). The REFIN/REFOUT pin of the AD7607,
configured in internal reference mode, should be decoupled
using a 10 μF ceramic decoupling capacitor. The other AD7607
devices, configured in external reference mode, should use a
100 nF decoupling capacitor on their REFIN/REFOUT pins.
ADR421
Figure 37. Single External Reference Driving Multiple AD7607 REFIN Pins
REFIN/REFOUT
Figure 38. Internal Reference Driving Multiple AD7607 REFIN Pins.
AD7607
REF SELECT
REFIN/REFOUT
AD7607
REFIN/REFOUT
REF SELECT
0.1µF
+
10µF
2.5V
REF
V
DRIVE
100nF
Figure 36. Reference Circuitry
BUF
REFIN/REFOUT
AD7607
REF SELECT
REFIN/REFOUT
SAR
AD7607
REF SELECT
100nF
REFCAPB
REFCAPB
100nF
REFIN/REFOUT
10µF
AD7607
REFIN/REFOUT
REF SELECT
AD7607
REF SELECT
AD7607
100nF
100nF