ISL28278 Datasheet, PDF (12/13 Pages) Intersil Corporation – Dual Micropower Single Supply Rail-to-Rail Input and Output (RRIO) Precision Op-Amp

ISL28278, ISL28478
components can be mounted to the PC board using Teflon
standoff insulators.
HIGH IMPEDANCE INPUT
IN
V+
1/2 ISL28278
1/4 ISL28478
FIGURE 38. GUARD RING EXAMPLE FOR UNITY GAIN
AMPLIFIER
Example Application
Thermocouples are the most popular temperature-sensing
device because of their low cost, interchangeability, and
ability to measure a wide range of temperatures. The
ISL28278 (Figure 39) is used to convert the differential
thermocouple voltage into single-ended signal with 10X gain.
The ISL28278's rail-to-rail input characteristic allows the
thermocouple to be biased at ground and the amplifier to run
from a single 5V supply.
R₄
R₃ 10kΩ
R₂
K TYPE
THERMOCOUPLE
10kΩ
100kΩ
+ ^V+
ISL28278
-
V-
+
5V
410µV/°C
R₁
100kΩ
FIGURE 39. THERMOCOUPLE AMPLIFIER
Current Limiting
The ISL28278 and ISL28478 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_JMAX) for all 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 Eq.1.:
T_JMAX = T_MAX + (θ_JAxPD_MAXTOTAL)
(EQ. 1)
where:
• P_DMAXTOTAL is the sum of the maximum power
dissipation of each amplifier in the package (PD_MAX)
• PD_MAX for each amplifier can be calculated as shown in
Eq.2:
PD_MAX
=
2*V_S × I_SMAX + (V_S
-
V_OUTMAX
)
×
V_{-----O----U----T----M-----A----X--}
R_{L (EQ.}
2)
where:
• T_MAX = Maximum ambient temperature
• θ_JA = Thermal resistance of the package
• PD_MAX = Maximum power dissipation of 1 amplifier
• V_S = Supply voltage
• I_MAX = Maximum supply current of 1 amplifier
• V_OUTMAX = Maximum output voltage swing of the
application
• R_L = Load resistance
12
FN6145.1
September 28, 2006