EL8178

FN7504 Rev 7.00

Page 10 of 13

May 14, 2008

when evaluating the active amplifier’s performance in Mux

Amp configurations.

Note that feed through from the IN+ to IN- pins occurs on any

Mux Amp disabled channel where the input differential voltage

for small signal applications. In any application where two or

more amplifier outputs are muxed, use series IN+ resistors, or

current low enough to minimize the impact on the active

channel. See “Usage Implications” on page 10 for more

details.

IN+ and IN- Input Protection

In addition to ESD protection diodes to each supply rail, the

EL8178 has additional back-to-back protection diodes across

the differential input terminals. If the magnitude of the differential

will conduct. For elevated temperatures, the leakage of the

protection diodes (see Circuit 1 in “Pin Descriptions” on page 9)

18 and 19.

USAGE IMPLICATIONS

If the input differential voltage is expected to exceed 0.5V, an

external current limiting resistor must be used to ensure the input

current never exceeds 5mA. For noninverting unity gain

applications, the current limiting can be via a series IN+ resistor,

or via a feedback resistor of appropriate value. For other gain

configurations, the series IN+ resistor is the best choice, unless

sufficiently large to limit the input current to 5mA.

Large differential input voltages can arise from several

sources:

1. During open loop (comparator) operation. The IN+ and IN-

input voltages don’t track.

2. When the amplifier is disabled but an input signal is still

the varying IN+ signal creates a differential voltage. Mux

Amp applications are similar, except that the active channel

3. When the slew rate of the input pulse is considerably faster

the IN+ signal, a differential voltage results, and visible

distortion occurs on the input and output signals. To avoid

this issue, keep the input slew rate below 0.2V/µs, or use

appropriate current limiting resistors.

Large (>2V) differential input voltages can also cause an

EN I

nput Protection

The EN input has internal ESD protection diodes to both the

positive and negative supply rails, limiting the input voltage

range to within one diode beyond the supply rails (see “Circuit 2”

diagram on page 9). If the input voltage is expected to exceed

V+ or V-, then an external series resistor should be added to

limit the current to 5mA.

Output Current Limiting

The EL8178 has no internal current-limiting circuitry. If the

output is shorted, it is possible to exceed the “Absolute

Maximum Rating” for “operating junction temperature”,

potentially resulting in the destruction of the device.

Power Dissipation

It is possible to exceed the +150°C maximum junction

applications to determine if power supply voltages, load

conditions, or package type need to be modified to remain in

the safe operating area. These parameters are related in

Equation 1:

where:

•

application



+

=

(EQ. 1)



----------------------------



+



=

(EQ. 2)