Automotive Amp Isolates High Voltages, Yields Ratiometric Output

What you’ll learn:

• Why battery-powered traction-motor battery packs need a high-voltage isolation amplifier
• How this Texas Instruments iso amp meets stringent application requirements and standards.
• How an evaluation module simplifies assessment of this high-voltage product.

The days of the automotive and other battery-powered/assisted vehicles being 12-V-only systems that you could easily measure with low-voltage components or troubleshoot with a multimeter — without worries about personal safety — are long gone (okay, those 12-V ICE cars do have high-voltage spark plugs). For irrefutable evidence of this reality shift, take a look at the AMC0381R-Q1 analog amplifier from Texas Instruments.

This is a precision, galvanically (ohmic) isolated amplifier with a high-voltage DC, high-impedance input, and single-ended ratiometric output. Its input connects directly to a high-voltage signal source, such as the battery pack of a traction motor in an EV, for direct DC-voltage sensing without external resistors.

In a typical application, the high-voltage (HV) domain includes the HV battery and the power stage of the traction inverter. The low-voltage domain incorporates the system controller and human interface. The controller must measure the DC-bus voltage while remaining galvanically isolated from the high-voltage domain for safety reasons. The AMC0381R-Q1 enables this measurement due to its high-impedance input and galvanically isolated output (Fig. 1).

The isolation barrier separates the parts of the system that operate on different common-mode voltage levels. This barrier is highly resistant to magnetic interference and certified to provide reinforced isolation up to 5 kV RMS (60 seconds). The iso amp also meets CISPR-11 and CISPR-25 EMI limits.

Note the somewhat unusual 15-pin, 0.65-mm pitch, 12.8- × 10.3-mm SSOP package, which is among the tactics needed to meet the physical creep and clearance standards for the reinforced isolation barrier (Fig. 2).

The AEC-Q100-qualified AMC0381R-Q1 is available in three linear input-voltage ranges of 600, 1,000, and 1,600 V. With its integrated precision resistive divider, the AMC0381RQ1 achieves better than 1% accuracy over the full −40 to +125°C temperature range, including lifetime drift. Beyond CISPR-11 and CISPR-25, the component meets relevant DIN EN IEC 60747-17 (VDE 0884-17) and UL 1577 isolation requirements.

Potential users of this type of component would undoubtedly like to assess its capabilities before going to a full-scale design-in. TI offers the AMC038XEVM Evaluation Module, which demonstrates a high-precision, high-voltage sensing design (Fig. 3). The evaluation module can measure up to 1600-V inputs without the need for external voltage-divider resistors.

The evaluation board also includes a discrete power section to generate the high-side supply from the low-side supply. Furthermore, screw terminals make for easy access to inputs and outputs. The detailed 20-page datasheet includes full setup and use instructions as well as bill of materials, schematic diagram, and PCB layout images.