US72/73

Single Coil Fan Driver

3901090261

Page 4 of 9

Data Sheet

Rev. 002

May/04

4. US72/73 Magnetic Specifications

Parameter

Symbol

Test Conditions

Min

Typ

Max

Units

Operate Point

Bop

3.0

6.0

mT

Release Point

Brp

-6.0

-3.0

mT

Hysteresis

Hys

6.0

mT

Note:

1 mT = 10 Gauss

5. General Description

The US72 / US73 provide a one-chip solution for 2-wire or 3-wire fans with a single coil winding. The chip

contains the Hall-effect sensor, dynamic offset correction, and power drivers in a single package. The

output drivers and supply pins are fully protected against switching transients. The FG or RD open-drain

signal outputs are compatible with any TTL or CMOS logic input.

6. Unique Features

The switching of the load current is controlled to limit current slew-rate, and eliminate shoot-through

currents. The 200uS (typical) recirculation allows the current to decay, reducing the switching noise.

The built-in locked-rotor protection will automatically shut off the coil current when the rotor is

mechanically blocked, or the rotational speed drops below 60 RPM. The fan will try to restart every 1.5

seconds until the obstruction is clear. The On / Off cycling reduces the average stall current to 1/6

normal; this is enough to prevent overheating or damage to most fans.

A common two-coil fan with unipolar drivers only uses half of the coil windings at any time. The one-coil

design with full-bridge drivers uses all the windings all the time to generate torque. This generally allows

for a smaller, more efficient stator design.