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INA188

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SBOS632 – SEPTEMBER 2015

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7.3.5 Input Protection and Electrical Overstress

Designers often ask questions about the capability of an 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

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 its relevance to an electrical overstress event is

helpful. The Functional Block Diagram section illustrates the ESD circuits contained in the INA188. 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. This protection circuitry is intended to remain inactive during normal

circuit operation.

The input pins of the INA188 are protected with internal diodes connected to the power-supply rails. These

diodes clamp the applied signal to prevent the input circuitry from being damaged. If the input signal voltage can

exceed the power supplies by more than 0.3 V, limit the input signal current to less than 10 mA to protect the

internal clamp diodes. This current limiting can generally be done with a series input resistor. Some signal

sources are inherently current-limited and do not require limiting resistors.

7.3.6 Input Common-Mode Range

The linear input voltage range of the INA188 input circuitry extends from 100 mV inside the negative supply

voltage to 1.5 V below the positive supply, and maintains 84-dB (minimum) common-mode rejection throughout

this range. The common-mode range for most common operating conditions is best calculated using the INA

common-mode range calculating tool. The INA188 can operate over a wide range of power supplies and VREF

configurations, thus providing a comprehensive guide to common-mode range limits for all possible conditions is

impractical.

The most commonly overlooked overload condition occurs when a circuit exceeds the output swing of A1 and A2,

which are internal circuit nodes that cannot be measured. Calculating the expected voltages at the output of A1

and A2 (see the Functional Block Diagram section) provides a check for the most common overload conditions.

The designs of A1 and A2 are identical and the outputs can swing to within approximately 250 mV of the power-

supply rails. For example, when the A2 output is saturated, A1 can continue to be in linear operation, responding

to changes in the noninverting input voltage. This difference can give the appearance of linear operation but the

output voltage is invalid.

7.4 Device Functional Modes

7.4.1 Single-Supply Operation

The INA188 can be used on single power supplies of 4 V to 36 V. Use the output REF pin to level shift the

internal output voltage into a linear operating condition. Ideally, connecting the REF pin to a potential that is mid-

supply avoids saturating the output of the input amplifiers (A1 and A2). Actual output voltage swing is limited to

250 mV above ground when the load is referred to ground. The typical characteristic curves, Output Voltage

Swing vs Output Current (Figure 19 to Figure 22) illustrates how the output voltage swing varies with output

current. See the Driving the Reference Pin section for information on how to adequately drive the reference pin.

With single-supply operation, VIN+ and VIN– must both be 0.1 V above ground for linear operation. For instance,

the inverting input cannot be connected to ground to measure a voltage connected to the noninverting input.