OPA698 Datasheet, PDF (25/27 Pages) Texas Instruments – Unity-Gain Stable, Wideband Voltage Limiting Amplifier

g) When long traces are necessary, use transmission line
design techniques (consult an ECL design handbook for
microstrip and stripline layout techniques). A 50Ω transmis-
sion line is not required on board—a higher characteristic
impedance will help reduce output loading. Use a matching
series resistor at the output of the op amp to drive a
transmission line, and a matched load resistor at the other
end to make the line appear as a resistor. If the 6dB of
attenuation that the matched load produces is not accept-
able, and the line is not too long, use the series resistor at the
source only. This will isolate the source from the reactive load
presented by the line, but the frequency response will be
degraded. Multiple destination devices are best handled as
separate transmission lines, each with its own series source
and shunt load terminations. Any parasitic impedances act-
ing on the terminating resistors will alter the transmission line
match, and can cause unwanted signal reflections and reac-
tive loading.
h) Do not use sockets for high-speed parts like the OPA698.
The additional lead length and pin-to-pin capacitance intro-
duced by the socket creates an extremely troublesome
parasitic network. Best results are obtained by soldering the
part onto the board.
POWER SUPPLIES
The OPA698 is nominally specified for operation using either
±5V supplies or a single +5V supply. The maximum specified
total supply voltage of 12V allows reasonable tolerances on
the supplies. Higher supply voltages can break down internal
junctions, possibly leading to catastrophic failure. Single-
supply operation is possible as long as common mode
voltage constraints are observed. The common-mode input
and output voltage specifications can be interpreted as a
required headroom to the supply voltage. Observing this
input and output headroom requirement will allow design of
non-standard or single-supply operation circuits. Figure 2
shows one approach to single-supply operation.
INPUT AND ESD PROTECTION
ESD damage has been known to damage MOSFET devices,
but any semiconductor device is vulnerable to ESD damage.
This is particularly true for very high-speed, fine geometry
processes. ESD damage can cause subtle changes in ampli-
fier input characteristics without necessarily destroying the
device. In precision operational amplifiers, this may cause a
noticeable degradation of offset voltage and drift. Therefore,
ESD handling precautions are required when handling the
OPA698.
External
Pin
+V_CC
–V _CC
FIGURE 26. Internal ESD Protection.
Internal
Circuitry
OPA698
25
SBOS258B
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