You can use this chart to calculate approximate probability of a specification in a unit; for example, the INA351

typical input voltage offset is 200 µV, so 68.2% of all INA351 devices are expected to have an offset from –200

µV to +200 µV. At 4 σ (±800 µV), 99.9937% of the distribution has an offset voltage less than ±800 µV, which

means 0.0063% of the population is outside of these limits, which corresponds to about 1 in 15,873 units.

Specifications with a value in the minimum or maximum column are verified by TI, and units outside these limits

are removed from production material. For example, the INA351 family has a maximum offset voltage of 1.3 mV

at 25°C, and even though this corresponds to 6 σ (≈1 in 500 million units), which is extremely unlikely, TI verifies

that any unit with larger offset than 1.3 mV are removed from production material.

For specifications with no value in the minimum or maximum column, consider selecting a sigma value of

sufficient guard band for your application, and design worst-case conditions using this value. As stated earlier,

the 6-σ value corresponds to about 1 in 500 million units, which is an extremely unlikely chance, and can be

an option as a wide guard band to design a system around. In this case, the INA351 family does not have a

maximum or minimum for offset voltage drift, but based on Figure 7-3 and the typical value of 0.65 µV/°C in

the Section 7.5 table, the 6-σ value for offset voltage drift can be calculated to 3.9 µV/°C. When designing for

worst-case system conditions, this value can be used to estimate the worst possible offset drift without having an

actual minimum or maximum value.

However, process variation and adjustments over time can shift typical means and standard deviations, and

unless there is a value in the minimum or maximum specification column, TI cannot verify the performance of a

device. This information must be used only to estimate the performance of a device.

8.3.5 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 8-5 shows the ESD circuits contained in the INA351 devices. 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 these diodes meet at an absorption device internal to the operational amplifier. This

protection circuitry is intended to remain inactive during normal circuit operation.

+

–

V+

V–

+IN

– IN

OUT

Power Supply

ESD Cell

REF

GS

SHDN

_____

Figure 8-5. Equivalent Internal ESD Circuitry

www.ti.com

INA351

SBOSAD5 – DECEMBER 2022

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