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The US91A is a one-chip solution for driving two-coil brushless DC cooling fans.

Based on Melexis CMOS process, the integrated circuit contains a Hall-effect sensor, dynamic offset correction and low side output drivers.

The integrated alarm (RD) output is a safety signal which allow to detect if the fan rotates or not. Its open-drain output facilitates the connectivity with external interface for hardware monitoring. These features are combined with the Melexis patented no-VDD design to fit the IC in a small 4-pin VK or VA package.  Also available in straight leads SOT23 and bent leads SOIC8 package.

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Top features

  • Low cost

  • High sensitivity Hall sensor

  • Locked rotor protection and auto-restart

  • Power-efficient CMOS and power MOSFETs

  • Built-in output protection clamping diode

  • Integrated alarm signal output

  • SIP- package options:  4-pin VK or VA

  • SMD package options: SOT23-5L straight leads and SOIC8 bent leads

  • Drop-in replacement of US91
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Two-coil fan driver - high voltage (alarm output) - US91A

Features and benefits

  • Low cost

  • High sensitivity Hall sensor

  • Locked rotor protection and auto-restart

  • Power-efficient CMOS and power MOSFETs

  • Built-in output protection clamping diode

  • Integrated alarm signal output

  • SIP- package options:  4-pin VK or VA

  • SMD package options: SOT23-5L straight leads and SOIC8 bent leads

  • Drop-in replacement of US91

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