Common-Mode Cmo Output Buffering; Voltage Reference; Power Supply Rails - Analog Devices EVAL-AD4080-FMCZ User Manual

User Guide
SUPPORTED CONFIGURATIONS
Stage 2 Bypass
By default, Stage 2 is enabled in the signal chain. To disable (by-
pass) Stage 2, the following hardware modifications are required:
Remove R10 and R11 to disconnect the Stage 2 input from the
►
Stage 1 output.
Remove R102 and R03 to disconnect the Stage 2 output from
►
the Stage 3 input.
Remove C75.
►
Populate R33 and R18 with 0 Ω resistors to bypass Stage 2.
►
Using an AMC (Stage 1 and Stage 2 Bypass)
The AMC is an Analog Devices, Inc., standard format for boards
containing an amplifier stage. Some examples of amplifiers availa-
ble on an AMC board follow:
AMC-ADA4940-1ARZ
►
AMC-ADA4896-2ARMZ
►
AMC-ADA4807-2ARMZ
►
AMC-ADA4805-2ARMZ
►
AMC-ADA4841-2ARMZ
►
The EVAL-AD4080-FMCZ includes the necessary connectors so
that an AMC can be fitted at the AFE, bypassing Stage 1 and
Stage 2, which requires Stage 1 and Stage 2 to be disabled and
disconnected.
The following must be done to use an AMC:
Remove R4, R6, R102, R103 to disconnect Stage 1 from the
►
signal chain input and Stage 2 from output.
Remove the C75 capacitor.
►
Populate the footprints of C67 and C79 with 0 Ω resistors to
►
ground the inputs of Stage 1.
Close Switch 1 and Switch 2 from Switch Array S1 (see
►
to power down the now unused U1 and U2 amplifiers.
To provide the correct power supply to the AMC for the JP19 and
►
JP20 solder links, do the following:
If using a fully differential amplifier AMC, link Pad 1 to Pad 2.
►
If using a single-ended amplifier AMC, link Pad 2 to Pad 3.
►
Stage 3 Bypass
By default, Stage 3 amplifiers are enabled in the signal chain. To
disable Stage 3, the following hardware modifications are required:
For the JP15, JP16, JP17, and JP18 solder links, remove the
►
default linkage (Pad 2 to Pad 3) and link Pad 1 to Pad 2 instead.

COMMON-MODE CMO OUTPUT BUFFERING

By default, the common-mode voltage output from the ADC (CMO
pin) is unbuffered and not connected to the V
ADA4945-1. To make that connection, the following hardware modi-
fication is required:
analog.com
Table 3)
pin of the
OCM
Populate R30 with a 0 Ω resistor.
►
To buffer the CMO output of the
amplifier, the following hardware modifications are required:
For the JP8 and JP9 solder links, remove the default linkage
►
(Pad 1 to Pad 2) and link Pad 2 to Pad 3 instead.
Remove R86.
►

VOLTAGE REFERENCE

Secondary Voltage Reference, LT6657-3
The default reference is the LTC6655-3
LT6657-3 (U36) secondary on-board reference, do the following:
Remove the R147 resistor to disconnect the U25 output from the
►
reference path.
Populate R146 with a 0 Ω resistor to connect U36 to the refer-
►
ence path.

POWER SUPPLY RAILS

Internal AD4080 LDO Regulators for the 1.1 V
Rails
By default, the two 1.1 V supply rails (VDD11 and IOVDD) required
by the AD4080 are supplied by on-board LDO regulators (U34 and
U35). The rails can be alternatively powered by two on-chip LDO
regulators internal to the AD4080; however, this requires discon-
necting the externally generated supplies from VDD11 and IOVDD
and connecting a voltage source in the 1.5 V to 2.75 V range at the
VDDLDO pin. The presence of this external voltage at the VDDLDO
pin automatically triggers the start up of the internal regulators. A 2
V, LDO regulator (U33)-generated rail on the EVAL-AD4080-FMCZ
is prepared for this function.
Therefore, to enable use of the on-chip LDO regulators, do the
following:
Remove the P9 and P10 jumpers to disconnect the AD4080 1.1
►
V supply inputs from the on-board generated rails.
Place a jumper across P6 to connect the 2 V rail to the VDDLDO
►
pin.
Off-Board Powering of Individual Power Rails
Any, or all of, the on-board power rails shown in the
section can be externally supplied to the evaluation hardware,
which can be useful for evaluating the AD4080 with different pow-
er solutions or for measuring the supply currents with benchtop
equipment. When providing power to power rails individually from
an alternative source, the user ensure that the source used can
provide sufficient voltage and current to properly supply the rail.
Failure to do so can result in damage to the on-board components.
EVAL-AD4080
AD4080 using an ADA4807-2
(U25). To instead use the
Power Supplies
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