US168 / US169

Low Noise & Low voltage

Single-Coil Fan/Motor Driver

390109027901

Page 5 of 13

Data Sheet

Rev 001

July/06

9 Detailed General Description

The US168/169 is an efficient one-chip solution for driving Brushless DC fans and motors. The IC includes

Hall-effect sensor, chopping amplifier for offset cancellation, digital control circuitry and full bridge output

driver.

The US168 has an open-drain tachometer FG output that follows the Hall signal.

In the US169, the open-drain alarm output RD is active low during normal spinning of the motor. It goes

high when the magnetic flux switching frequency drops below nearly 1Hz (30RPM for 2 pole-pair fan).

The FG/RD open drain output has an internal current limit. It can be activated if a low-ohmic pull-up

resistor is used or if the FG/RD output is short connected to a supply voltage.

The built-in locked rotor protection automatically shuts off the coil current when the rotor is mechanically

blocked for more than 0.4 second. The fan tries to restart every 2.8 seconds until the rotor is released.

This on/off cycling reduces the average current by factor of 7. It is enough to prevent fans from

overheating or damage.

the thermal protection stops the current flowing

through the full bridge by setting the outputs

OUT1 and OUT2 low and setting the output FG

(RD) high.

The IC stays in this state until the junction