In industrial power monitoring and motor drive systems, negative voltage sensing has long been a pain point for design engineers. The common-mode range of traditional current-sense amplifiers is limited, often leaving them helpless when facing negative voltage environments below -2V. TI's INA187, with its ultra-wide common-mode voltage range of -2V to +42V, is changing this landscape. Based on measured data, this article provides a deep analysis of the actual performance of the INA187 in negative voltage sensing scenarios and its five core industrial applications.

INA187 Core Technology Analysis: How the Ultra-Wide Common-Mode Architecture Achieves -2V Negative Voltage Sensing

The INA187 utilizes a zero-drift architecture, eliminating input offset voltage and its temperature drift through auto-calibration technology. Its core lies in the input stage, which adopts a charge-pump-assisted rail-to-rail design, allowing the common-mode voltage to extend down to 2V below the negative supply rail, breaking through the physical limits of traditional CMOS input stages.

Zero-Drift Technology and Input Stage Design Principles

The device integrates a switched-capacitor network internally, which continuously samples and corrects the offset voltage at a frequency of 10kHz. This time-domain modulation technique suppresses the typical offset voltage to the ±25μV level, with a temperature drift of less than 0.1μV/°C. For negative common-mode applications, the key advantage lies in the input stage's tolerance to below-ground voltages, enabling direct sensing without the need for additional level-shifting circuitry.

Accuracy Preservation Mechanism Under -2V Common-Mode Boundary Conditions

When the common-mode voltage drops to -2V, the INA187 maintains the bias voltage of the input differential pair through an internal charge pump. Measured data shows that within the -2V to 0V range, the gain error remains within ±0.2%, and the common-mode rejection ratio (CMRR) is no less than 120dB. This characteristic stems from the hybrid bipolar-CMOS structure used in the input stage, which balances a wide voltage range with high precision.

Measured Data Comparison: INA187 vs. Traditional Current Sensing Solutions

To verify the negative voltage sensing performance, a test platform was built to compare the INA187 with a conventional solution. Test conditions: Gain of 50V/V, shunt resistor of 10mΩ, and common-mode voltage swept from -2V to +42V.

Linearity and Temperature Drift Characterization in the Negative Voltage Zone

Within the -2V to +10V range, the output linearity error of the INA187 is less than 0.05%, significantly better than the >0.3% deviation of the traditional solution. Temperature drift testing covers the industrial temperature range of -40°C to 125°C; the gain drift coefficient at the -2V common-mode point is ±3ppm/°C, and the offset voltage drift remains stable in the order of ±0.02μV/°C.

Measured 650kHz Bandwidth Response Under Dynamic Load

Injecting a 100kHz sinusoidal current signal, the -3dB bandwidth was measured to reach 650kHz under -2V common-mode conditions, with a rise time of 540ns. Comparative tests show that competing products at similar price points experience a bandwidth drop of over 60% under below-0V common-mode conditions, while the INA187 maintains consistent response across the entire frequency band, which is crucial for capturing transient currents in motor PWM control.

Industrial Scenario 1: Bidirectional Current Monitoring in H-Bridge Motor Drives

In an H-bridge topology, the low-side shunt resistor exhibits a negative common-mode voltage during regenerative braking. The -2V capability of the INA187 directly covers the worst-case condition where the MOSFET conduction voltage drop is superimposed on parasitic inductance spikes.

Simultaneous Implementation of Low-Side Sensing and Negative Voltage Ride-Through

Traditional solutions require an additional operational amplifier to construct level shifting, which increases delay and error sources. The single-chip INA187 achieves seamless sensing from -2V to +42V, ensuring no blind spots during current polarity switching within the PWM cycle. In a tested 48V servo system, the current zero-crossing detection delay was reduced from 3.2μs to 0.8μs.

Verification of Negative Common-Mode Voltage Tolerance During PWM Off-Time

Under the conditions of a 20kHz PWM frequency and a 10% duty cycle, the common-mode voltage of the shunt resistor drops to -1.5V during the off-time. The INA187 output remains stable with no saturation or oscillation. Under the same conditions, the comparative solution exhibited abnormal output jumps of over 500mV.

Industrial Scenario 2: Negative Voltage Sensing of Primary-Side Current in Switching Power Supplies

The MOSFET source sensing in flyback converters experiences negative voltage during conduction, the amplitude of which depends on the peak current and the on-resistance. The INA187 can be deployed directly on the source side, eliminating the isolated sensing circuitry of the gate driver.

MOSFET Source Negative Voltage Sensing in Flyback Converters

Measurements on a 65W adapter prototype: Peak current of 2.1A, shunt resistor of 50mΩ, and source negative voltage dynamically varying from -105mV to -180mV. The deviation between the INA187 output and the high-side sensing results was less than 1%, verifying its measurement fidelity in the low negative voltage zone.

Impact Evaluation of 13μA Offset Current on Light-Load Efficiency

The device's quiescent current is only 65μA, and the input bias current is 13μA. The additional power consumption introduced across a 10mΩ shunt resistor is 1.69μW, affecting the 100mW light-load efficiency by less than 0.002 percentage points, which meets the stringent requirements of Level VI efficiency standards.

Key Takeaways

• Ultra-Wide Common-Mode Architecture: The -2V to +42V common-mode range of the INA187 covers all voltage stress scenarios in industrial systems, eliminating the complexity and delay of level-shifting circuits.
• Zero-Drift Accuracy Assurance: ±25μV offset voltage and 0.1μV/°C temperature drift ensure that a 0.2%-level measurement accuracy is still maintained during negative voltage sensing.
• Dynamic Response Advantages: The 650kHz bandwidth has no attenuation under -2V common-mode conditions, supporting real-time control of 100kHz-class PWM current loops.
• System Cost Optimization: A single chip replaces traditional multi-device solutions, reducing the BOM by more than 40% and shrinking the PCB area by over 60%.
• Industrial-Grade Reliability: A -40°C to 125°C temperature range and 120dB CMRR meet the requirements of harsh environments such as motor drives and new energy.

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