OPA1641-Q1 Datasheet, PDF (19/31 Pages) Texas Instruments – SoundPlus JFET-Input, Automotive-Grade, Audio Operational Amplifiers

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OPA1641-Q1, OPA1642-Q1
SBOS791 – JUNE 2017
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.
8.1.5 Electrical Overstress
Designers often ask questions about the capability of an operational amplifier to withstand electrical overstress.
These questions tend to focus on the device inputs, but can involve the supply voltage pins or even the output
pin. Each of these different pin functions have electrical stress limits determined by the voltage breakdown
characteristics of the particular semiconductor fabrication process and specific circuits connected to the pin.
Additionally, internal electrostatic discharge (ESD) protection is built into these circuits to protect them from
accidental ESD events both before and during product assembly.
Having a good understanding of this basic ESD circuitry and the relevance to an electrical overstress event is
helpful. Figure 36 illustrates the ESD circuits contained in the OPA164x-Q1 series (indicated by the dashed line
area). The ESD protection circuitry involves several current-steering diodes connected from the input and output
pins and routed back to the internal power-supply lines where an internal absorption device is connected. This
protection circuitry is intended to remain inactive during normal circuit operation.
An ESD event produces a short-duration, high-voltage pulse that is transformed into a short-duration, high-
current pulse when discharging through a semiconductor device. The ESD protection circuits are designed to
provide a current path around the operational amplifier core to prevent damage. The energy absorbed by the
protection circuitry is then dissipated as heat.
When an ESD voltage develops across two or more of the amplifier device pins, current flows through one or
more of the steering diodes. Depending on the path that the current takes, the absorption device can activate.
The absorption device has a trigger (or threshold voltage) that is above the normal operating voltage of the
OPA164x-Q1 but below the device breakdown voltage level. When this threshold is exceeded, the absorption
device quickly activates and clamps the voltage across the supply rails to a safe level.
When the operational amplifier connects into a circuit as shown in Figure 36, the ESD protection components are
intended to remain inactive and not become involved in the application circuit operation. However, circumstances
can arise where an applied voltage exceeds the operating voltage range of a given pin. If this condition occurs,
some of the internal ESD protection circuits can be biased on and conduct current. Any such current flow occurs
through steering diode paths and rarely involves the absorption device.
Figure 36 depicts a specific example where the input voltage (V_IN) exceeds the positive supply voltage (+V_S) by
500 mV or more. Much of what happens in the circuit depends on the supply characteristics. If +V_S can sink the
current, one of the upper input steering diodes conducts and directs current to +V_S. Excessively high current
levels can flow with increasingly higher V_IN. As a result, the data sheet specifications recommend that
applications limit the input current to 10 mA.
Copyright © 2017, Texas Instruments Incorporated
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