The Absolute Maximum Ratings table lists the maximum limits for voltage, temperature, and allowable current. Note that exceeding the Absolute Maximum Ratings may cause permanent damage to the device. This is a maximum rating only, and proper operation of the device should not be inferred at these or any other conditions beyond those shown in the operating section of this specification. Exposure to absolute maximum rating conditions for extended periods may affect device reliability.

There are many ways to build a successful circuit, but there are many more ways to destroy it, and 90% of the problems and failures we face are related to careless or misreading the data sheet.

Today we’re going to start with the specs in the data sheet and talk about some common questions about absolute maximum ratings, the answers to which may seem obvious, but are often misunderstood… Let’s get started and see if you’ve got the hang of it No ↓↓↓

Q: Can amplifier operating parameters be slightly higher than the absolute maximum ratings?

Absolutely not. The absolute maximum ratings specified in the data sheet must be followed to prevent permanent damage to the device. Absolute Maximum Ratings represent the limits to which the device can withstand, not the limits at which the device will operate.

For example, when the input voltage is greater than the absolute maximum rating, the result is a breakdown of the input differential pair of the op amp, causing excessive fault currents. Not only does this cause parametric performance changes, but it also causes metal migration, which can result in permanent damage to the device over time.

In short, keep your distance from the maximum ratings, or the device is likely to be destroyed!

The Absolute Maximum Ratings table lists the maximum limits for voltage, temperature, and allowable current. Note that exceeding the Absolute Maximum Ratings may cause permanent damage to the device. This is a maximum rating only, and proper operation of the device should not be inferred at these or any other conditions beyond those shown in the operating section of this specification. Exposure to absolute maximum rating conditions for extended periods may affect device reliability.

Be careful of falling into the pit!These specifications in the data sheet must be treated with caution
Figure 1. Example Table of Absolute Maximum Ratings

The maximum supply voltage that can be applied to an op amp depends on the manufacturing process. This refers to the instantaneous value, not the mean or final value. Our low-voltage CMOS op amps from ADI are generally limited to 6 V, and high-voltage bipolar devices are limited to 36 V.

The maximum input voltage depends on the op amp’s input stage architecture and supply voltage. Almost all op amps are protected by ESD diodes. The input ESD diode determines how much the input voltage can exceed the supply voltage. In general, the input voltage must not exceed one diode drop across the supply rail (approximately 300 mV to 700 mV, depending on temperature). When the operational voltage of the op amp exceeds the input voltage range but is within the absolute maximum value, its parametric performance changes. The op amp is not damaged, but may not function properly, for example, it may be out of phase and the input bias current or input offset voltage may increase substantially. Once the input voltage exceeds the absolute maximum, the op amp can suffer permanent damage.

A common problem that many people face is the presence of voltage at the input of an unpowered op amp (due to power supply sequencing). This would violate the absolute maximum rating limits, cause input overvoltage, and possibly destroy the device. An easy solution to this problem is to use an amplifier with integrated input overvoltage protection. Vendors have integrated on-chip input overvoltage protection circuitry as a convenient alternative to discrete analog solutions.

For example, ADI’s overvoltage protected (OVP) precision amplifier, the ADA4091-2, allows input voltages up to 25 V above or below the supply voltage without causing damage to the device.

The maximum differential input voltage refers to the maximum differential voltage that can be applied between the inputs without inducing excessive current. Some op amps (see Figure 2) utilize built-in back-to-back diodes to protect the input stage from base-emitter breakdown. The maximum input differential voltage can be roughly inferred from the number of clamping diodes between the inputs.

Be careful of falling into the pit!These specifications in the data sheet must be treated with caution
Figure 2. Input Differential Voltage Protection

The Absolute Maximum Ratings table also includes the maximum allowable input current at the input. If the data sheet does not provide information on the maximum input current, a good rule of thumb is to always limit the input current to less than 5 mA; if the input current is expected to be greater than the absolute maximum, insert a series resistor at the input to prevent current is limited. But doing so introduces noise and increases the input-referred offset voltage.

Q: Will the device fail immediately when the Absolute Maximum Ratings are exceeded?

When the Absolute Maximum Ratings are exceeded, there are several failure modes –

1
When the maximum ratings are exceeded, the device will fail immediately.

When excessive voltage is applied to an amplifier, say, a 30 V supply voltage to a 6 V CMOS amplifier, the built-in transistors or junctions fail almost immediately. The device can then be permanently damaged.

2
Exceeding the Absolute Maximum Ratings for an extended period of time could result in device failure.

Sometimes a device does not fail immediately when subjected to excessive voltage or current, but it will eventually suffer damage over time. For example, it might be acceptable to apply 7 V to a 6 V amplifier for short periods of time. However, when the device is continuously subjected to overvoltage, the junction becomes weak. Eventually, the device will fail. In this case, the long-term reliability of the device is greatly compromised.

3
Exceeding the absolute maximum ratings can result in degraded performance and overheating of the junction, which can eventually lead to device failure.

Excessive input current may cause parametric performance changes and metal migration. The junction thermal limit may also be exceeded as the heat builds up. Even if the junction thermal limits are not exceeded, higher junction operating temperatures can result in significant reductions in device lifetime.

in conclusion

To avoid any damage to the amplifier, it is necessary to prevent exceeding the absolute maximum ratings, and to extend the life of the device, it is also necessary to have a sufficient safety margin over the absolute maximum ratings.

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