8.1.4 Power Dissipation and Thermal Protection

The OPA164x-Q1 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 can be used, as long as the output current does not exceed 13 mA; otherwise, the device short-circuit current-protection circuit can activate.

Internal power dissipation increases when operating at high supply voltages. Copper leadframe construction used in the OPA164x-Q1 series of devices improves heat dissipation compared to conventional materials. PCB layout can help reduce a possible increase in junction temperature. Wide copper traces help dissipate the heat by functioning as an additional heat sink. 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 one or more output channels of a device can result in excessive heating. For instance, when an output is shorted to midsupply, 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 case of a dual OPA1642-Q1 in an VSSOP-8 package (thermal resistance R_θJA = 180°C/W), such a power dissipation results in the die temperature to be 220°C above ambient temperature, when both channels are shorted. This temperature increase destroys the device.

To prevent such excessive heating that can destroy the device, the OPA164x-Q1 series has an internal thermal shutdown circuit that 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.