UG-474 Evaluation Board User Guide
Rev. 0 | Page 4 of 8
EVALUATION BOARD HARDWARE
POWER SUPPLIES
Power is applied to the evaluation board through the TVCC
and TVEE test points (see Figure 3). The board accommodates
single or dual supplies. For single-supply operation, connect the
negative supply to the ground plane.
It is very important that the power supply pins of the device
under test (DUT) have broadband decoupling circuitry. The
board layout facilitates this with footprints for 0508 ceramic
capacitors (CVCC2 and CVEE2) on each supply, as well as 0402
ceramic capacitors (CVCC1 and CVEE1). Bulk decoupling is
provided by CVCC3 and CVEE3; 10 µF tantalum capacitors
are recommended.
FEEDBACK NETWORKS AND INPUT/OUTPUT
TERMINATIONS
Resistors RGN and RFN comprise the negative resistive feedback
loop, and Resistors RGP and RFP comprise the positive feedback
loop (see Figure 3). To minimize summing node capacitances,
the ground plane under and around Pin 1 and Pin 8 of the DUT
and the copper that connects to them have been removed.
Resistors RTN and RTP are included as input termination resistors
for applications that have single-ended inputs.
V
OCM
INPUT
An external voltage can be applied to the V
OCM
pin via the
TVOCM test point (referenced to the ground plane of the board).
In ADC driver applications, it is convenient to apply the ADC dc
reference voltage output directly. The CVOM component position
can be used for both resistors and capacitors. A 0.1 μF capacitor
is used in normal applications to provide bypassing for the dc
voltage applied to the V
OCM
pin.
It is also possible to drive the V
OCM
input from an external ac
source. In this case, omit CVOM, or reduce it to a value that
allows the desired signal to be passed.
COMMON-MODE VOLTAGE
The internal common-mode feedback loop used in the differen-
tial drivers forces the output common-mode voltage to be equal
to the voltage applied to the V
OCM
input, thereby providing
excellent output balance.
SMA INPUT/OUTPUT CONNECTORS
The inputs and outputs have edge-mounted SMA connectors
for convenient connection to coaxial cables. The recommended
connector is Part No. 142-0701-801 from Johnson Components,
or equivalent.
