ISL28276EVAL1Z Intersil, ISL28276EVAL1Z Datasheet - Page 17

• Manufacturer Part Number: ISL28276EVAL1Z
• Description: EVALUATION BOARD FOR ISL28276
• Manufacturer: Intersil

Specifications of ISL28276EVAL1Z

• Channels Per Ic: 2 - Dual
• Amplifier Type: General Purpose
• Output Type: Single-Ended, Rail-to-Rail
• Slew Rate: 0.17 V/µs
• Current - Output / Channel: 31mA
• Operating Temperature: -40°C ~ 125°C
• Current - Supply (main Ic): 120µA
• Voltage - Supply, Single/dual (±): 2.4 V ~ 5.5 V, ±1.2 V ~ 2.75 V
• Board Type: Fully Populated
• Utilized Ic / Part: ISL28276
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• -3db Bandwidth: -

Enable/Disable Feature
The ISL28276 (QSOP package only) offers two EN pins
(EN_A and EN_B) which disable the op amp when pulled up
to at least 2.0V. In the disabled state (output in a high
impedance state), the part consumes typically 4µA. By
disabling the part, multiple parts can be connected together
as a MUX. The outputs are tied together in parallel and a
channel can be selected by the EN pins. The loading effects
of the feedback resistors of the disabled amplifier must be
considered when multiple amplifier outputs are connected
together. 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.
Using Only One Channel
The ISL28276 and ISL28476 are dual and quad channel
op amps. If the application only requires one channel when
using the ISL28276 or less than 4 channels when using the
ISL28476, the user must configure the unused channel(s) to
prevent them from oscillating. The unused channel(s) 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 59).
Proper Layout Maximizes Performance
To achieve the maximum performance of the high input
impedance and low offset voltage, care should be taken in
the circuit board layout. The PC board surface must remain
clean and free of moisture to avoid leakage currents
between adjacent traces. Surface coating of the circuit board
will reduce surface moisture and provide a humidity barrier,
reducing parasitic resistance on the board. When input
leakage current is a concern, the use of guard rings around
the amplifier inputs will further reduce leakage currents.
Figure 60 shows a guard ring example for a unity gain
amplifier that uses the low impedance amplifier output at the
same voltage as the high impedance input to eliminate
surface leakage. The guard ring does not need to be a
specific width, but it should form a continuous loop around
both inputs. For further reduction of leakage currents,
components can be mounted to the PC board using Teflon
standoff insulators.
FIGURE 59. PREVENTING OSCILLATIONS IN UNUSED
CHANNELS
+
-
17
1/2 ISL28276
1/4 ISL28476
ISL28176, ISL28276, ISL28476
Current Limiting
The ISL28176, ISL28276 and ISL28476 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 +150°C maximum junction
temperatures under certain load and power-supply
conditions. It is therefore important to calculate the
maximum junction temperature (T
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 as follows:
where:
• P
• PD
where:
• T
• θ
• PD
• V
• I
• V
• R
T
PD
JMAX
FIGURE 60. GUARD RING EXAMPLE FOR UNITY GAIN
dissipation of each amplifier in the package (PD
application
MAX
MAX
JA
DMAXTOTAL
MAX
S
OUTMAX
L
MAX
MAX
= Load resistance
= Supply voltage (Magnitude of V
= Thermal resistance of the package
HIGH IMPEDANCE INPUT
=
= Maximum supply current of 1 amplifier
=
= Maximum ambient temperature
IN
T
for each amplifier can be calculated as follows:
2*V
= Maximum power dissipation of 1 amplifier
MAX
= Maximum output voltage swing of the
AMPLIFIER
S
+
×
is the sum of the maximum power
(
I
θ
SMAX
JA
xPD
+
(
MAXTOTAL
V
S
- V
OUTMAX
JMAX
V
)
+
+
) for all applications
and V
)
×
V
--------------------------- -
OUTMAX
-
R
)
L
MAX
June 23, 2009
FN6301.4
(EQ. 1)
(EQ. 2)
)