AD8244-EVALZ User Guide UG-650
Rev. 0 | Page 3 of 8
EVALUATION BOARD HARDWARE
POWER SUPPLIES
Power is applied to the board through test points +VS and −VS
(see Figure 2). The board accommodates single or dual supplies.
For single-supply operation, connect the negative supply to
ground.
It is very important that the power supply pins of the AD8244
have decoupling circuitry. The board layout facilitates this with
0.1 µF, 0805 ceramic capacitors (C3 and C4) on each supply.
Lower frequency decoupling is provided by C1 and C2, which
are D-size, 10 µF tantalum capacitors.
BOARD OPTIONS
The AD8244-EVA LZ board comes installed with the default
components listed in Table 1. The default configuration has
no added source impedance or output load. In addition to the
default, the board is easily configurable to test the AD8244 with
source impedance and load impedance.
The user may remove the zero Ω resistor in series with the
AD8244 input and install SMD or through-hole components
to represent the source impedance.
The user may load the AD8244 with resistance or capacitance
using 0805 components at RX2 (which refers to RA2, RB2, RC2,
and RD2 depending upon whether it is in channel A, B, C, or
D), RX3, and CX1. RX2 is in series with the outputs. RX3 and
CX1 may be used to form a snubber, which is an RC network
placed between the output of an amplifier and ground to
improve step response and stability with capacitive loads.
Before installing any components at RX2 or at RX3, be sure to
cut the short between the pads with a box cutter or similar tool.
SMA INPUT/OUTPUT CONNECTORS
The inputs and outputs of every channel have end-launch SMA
connector footprints (which are also compatible with some
SMB connector footprints) for convenient connection to coaxial
cables. The recommended connectors are Johnson/Emerson
142-0701-851 (SMA jack), 142-0801-811 (SMA plug), 131-
3701-801 (SMB jack), or equivalent footprint connectors.
GUARDING
The inputs of each channel of the AD8244 are guarded to
reduce leakage and parasitic capacitance at the inputs. In order
for the guard to be effective against leakage contamination on
the surface of the board, the solder mask is removed from the
top of the guard traces. During rework, take care that the guard
does not accidentally become shorted to a nearby node. See the
AD8244 data sheet for more information about guarding.
