US890 Melexis Company, US890 Datasheet - Page 9

• Manufacturer Part Number: US890
• Description: Two-coil Fan Driver ? High Output Curren
• Manufacturer: Melexis Company

The application 13.1 shows the typical application including a diode D1 for additional reverse voltage
protection. Without this diode, the reverse current in each coil is equal to the fan peak current, as it is only
limited by its coil resistances. In some fan construction where the peak current is not so big, this situation
may be acceptable by both IC and coils for short period of time. However, a long exposure may seriously
affect the reliability or damage each of them by overheating.
The diode D1 connected in series between the supply voltage and the common point of the coils prevents
this reverse current to flow. It prevents such reverse voltage damage and best protects both IC and coils.
The application 13.2 is given in case the ground connection might be disconnected while the fan operates. At
this moment, the current flowing through the coils may circulate from the output (OUT1 or OUT2) to the
FG/RD output driver in reverse direction. High reverse current may damage the logic output driver.
A bypass capacitor connected between the coil common node and the device ground should prevent such
damage occurring by providing a close path to this current.
The value of the capacitor needs to be tuned with the motor characteristics. Higher inductance may require
higher capacitor value.
For 2-wire fan application (tachometer or alarm logical output not required), the FG/RD pin (#1) should be
connected to the device ground pin (#4).
3901000890
Rev 002
13 Application Information
13.1 Typical application circuit
14 Application Comments
Two-Coil Fan Driver – High Output Current
Page 9 of 12
13.2 Recommended circuit for ground
disconnection protection
US890 / US891
Data Sheet
Sep/07