OPA1622 Datasheet, PDF (15/36 Pages) Texas Instruments – OPA1622 SoundPlus™ High-Fidelity, Bipolar-Input, Audio Operational Amplifier

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OPA1622
SBOS727A – NOVEMBER 2015 – REVISED NOVEMBER 2015
Feature Description (continued)
In order to calculate the worst-case power dissipation in the op amp, the ac and dc cases must be considered
separately.
In the case of constant output current (dc) to a resistive load, the maximum power dissipation in the op amp
occurs when the output voltage is half the positive supply voltage. This calculation assumes that the op amp is
sourcing current from the positive supply to a grounded load. If the op amp sinks current from a grounded load,
modify Equation 2 to include the negative supply voltage instead of the positive.
§V · V ²
P_{OPA(MAX _ DC)} P_{OPA ¨© 2 ¸¹ 4RL}
(2)
The maximum power dissipation in the op amp for a sinusoidal output current (ac) to a resistive load occurs
when the peak output voltage is 2/π times the supply voltage, given symmetrical supply voltages:
§ 2V · 2 ˜ V ²
P_{OPA(MAX _ AC)} P_{OPA ¨© S ¸¹ S2 ˜ RL}
(3)
The dominant pathway for the OPA1622 to dissipate heat is through the package thermal pad and pins to the
PCB. Copper leadframe construction used in the OPA1622 improves heat dissipation compared to conventional
materials. PCB layout greatly affects thermal performance. Connect the OPA1622 package thermal pad to a
copper pour at the most negative supply potential. This copper pour can be connected to a larger copper plane
within the PCB using vias to improve power dissipation. Figure 42 shows an analogous thermal circuit that can
be used for approximating the junction temperature of the OPA1622. The power dissipated in the OPA1622 is
represented by current source P_D; the ambient temperature is represented by voltage source 25ºC; and the
junction-to-board and board-to-ambient thermal resistances are represented by resistors θ_JB and θ_BA,
respectively. The board-to-ambient thermal resistance is unique to every application. The sum of θ_JB and θ_BA is
the junction-to-ambient thermal resistance of the system. The value for junction-to-ambient thermal resistance
reported in the Thermal Information table is determined using the JEDEC standard test PCB. The voltages in the
analogous thermal circuit at the points T_J and T_PCB represent the OPA1622 junction and PCB temperatures,
respectively.
TJ
JB (22.0ºC/W)
TPCB
BA
PD
25ºC
Figure 42. Approximate Thermal System Model of the OPA1622 Soldered to a PCB.
7.3.2 Thermal Shutdown
If the junction temperature of the OPA1622 exceeds 175ºC, a thermal shutdown circuit disables the amplifier in
order to protect the device from damage. The amplifier is automatically re-enabled after the junction temperature
falls below approximately 160ºC. If the condition that caused excessive power dissipation has not been removed,
the amplifier oscillates between a shutdown and enabled state until the output fault is corrected.
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