OPA698 datasheet(25/27 Pages) TI

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OPA698

SBOS258B

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g) When long traces are necessary, use transmission line

design techniques (consult an ECL design handbook for

microstrip and stripline layout techniques). A 50

Ω 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

External

–V

Internal

Circuitry

FIGURE 26. Internal ESD Protection.

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.

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