10

FN6154.4

February 11, 2008

pin. The EN pin also has an internal pull-down. If left open, the

EN pin will pull to the negative rail and the device will be

enabled by default.

The loading effects of the feedback resistors of the disabled

amplifier must be considered when multiple amplifier outputs

are connected together.

Using Only One Channel

The ISL28256 is a dual op amp. If the application only

requires one channel, the user must configure the unused

channel to prevent it from oscillating. The unused channel

will oscillate if the input and output pins are floating. This will

result in higher than expected supply currents and possible

noise injection into the channel being used. The proper way

to prevent this oscillation is to short the output to the

negative input and ground the positive input (as shown in

Figure 36).

Current Limiting

These devices have no internal current-limiting circuitry. If

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

Maximum Rating for output current or power dissipation,

potentially resulting in the destruction of the device.

Power Dissipation

It is possible to exceed the +125°C maximum junction

temperatures under certain load and power-supply

conditions. It is therefore important to calculate the

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 using

Equation 1:

where:

where:

•

application

FIGURE 36. PREVENTING OSCILLATIONS IN UNUSED

CHANNELS

-

+

T

JMAX

T

MAX

θ

()

+

=

(EQ. 1)

PD

MAX

2*V

S

I

SMAX

V

S

(

- V

V

OUTMAX

R

L

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

×

+

×

=

(EQ. 2)

ISL28156, ISL28256