OPA140_15 Datasheet, PDF (19/44 Pages) Texas Instruments – High-Precision, Low-Noise, Rail-to-Rail Output,11-MHz JFET Op Amp

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OPA140, OPA2140, OPA4140
SBOS498B – JULY 2010 – REVISED NOVEMBER 2015
Feature Description (continued)
7.3.6 Phase-Reversal Protection
The OPA140, OPA2140, and OPA4140 family has internal phase-reversal protection. Many FET- and bipolar-
input op amps exhibit a phase reversal when the input is driven beyond its linear common-mode range. This
condition is most often encountered in noninverting circuits when the input is driven beyond the specified
common-mode voltage range, causing the output to reverse into the opposite rail. The input circuitry of the
OPA140, OPA2140, and OPA4140 prevents phase reversal with excessive common-mode voltage; instead, the
output limits into the appropriate rail (see Figure 21).
7.3.7 Thermal Protection
The OPAx140 series of op amps are capable of driving 2-kΩ loads with power-supply voltages of up to ±18 V
over the specified temperature range. In a single-supply configuration, where the load is connected to the
negative supply voltage, the minimum load resistance is 2.8 kΩ at a supply voltage of 36 V. For lower supply
voltages (either single-supply or symmetrical supplies), a lower load resistance may be used, as long as the
output current does not exceed 13 mA; otherwise, the device short circuit current protection circuit may activate.
Internal power dissipation increases when operating at high supply voltages. Copper leadframe construction
used in the OPA140, OPA2140, and OPA4140 series devices improves heat dissipation compared to
conventional materials. Printed-circuit-board (PCB) layout can also help reduce a possible increase in junction
temperature. Wide copper traces help dissipate the heat by acting as an additional heatsink. Temperature rise
can be further minimized by soldering the devices directly to the PCB rather than using a socket.
Although the output current is limited by internal protection circuitry, accidental shorting of one or more output
channels of a device can result in excessive heating. For instance, when an output is shorted to mid-supply, the
typical short-circuit current of 36 mA leads to an internal power dissipation of over 600 mW at a supply of ±18 V.
In the case of a dual OPA2140 in an 8-pin VSSOP package (thermal resistance θ_JA = 180°C/W), such power
dissipation would lead the die temperature to be 220°C above ambient temperature, when both channels are
shorted. This temperature increase significantly decreases the operating life of the device.
To prevent excessive heating, the OPAx140 series has an internal thermal shutdown circuit, which shuts down
the device if the die temperature exceeds approximately 180°C. When this thermal shutdown circuit activates, a
built-in hysteresis of 15°C ensures that the die temperature must drop to approximately 165°C before the device
switches on again.
Additional consideration should be given to the combination of maximum operating voltage, maximum operating
temperature, load, and package type. Figure 35 and Figure 36 show several practical considerations when
evaluating the OPA2140 (dual version) and the OPA4140 (quad version).
As an example, the OPA4140 has a maximum total quiescent current of 10.8 mA (2.7 mA/channel) over
temperature. The 14-pin TSSOP package has a typical thermal resistance of 135°C/W. This parameter means
that because the junction temperature should not exceed 150°C to ensure reliable operation, either the supply
voltage must be reduced, or the ambient temperature should remain low enough so that the junction temperature
does not exceed 150°C. This condition is illustrated in Figure 35 for various package types. Moreover, resistive
loading of the output causes additional power dissipation and thus self-heating, which also must be considered
when establishing the maximum supply voltage or operating temperature. To this end, Figure 36 shows the
maximum supply voltage versus temperature for a worst-case dc load resistance of 2 kΩ.
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