US651 Datasheet, PDF (9/12 Pages) Melexis Microelectronic Systems – Two-Coil Low Noise Fan Driver

12 Application Information
US651 / US661
Two-Coil Low Noise Fan Driver
Typical computer fan application circuit
13 Application Comments
During fan rotation, the coils may affect the stability of the V_DD voltage. To filter eventual spikes, it is
recommended to add a 100nF decoupling capacitor between V_DD pin and GND, closer to the chip.
If the FG/RD pull-up resistor is connected to V_DD, a diode should be connected between the fan supply
voltage and the common point of the fan coils to avoid parasitic effects on FG/RD output.
The voltage V_DD and V_PU can be physically the same voltage source. However, the pull-up voltage V_PU is
generally connected to a different digital power source at 5V as it feeds the FG or RD signal to an IC
interface.
When the default slope is sufficient, the pin SLOPE may just be left open.
For slope adjustment, it is required to connect a resistor R_SLOPE between the SLOPE pin to ground. The value
of the resistor modifies the output slope as shown in the performance graph.
390109020902
Rev 002
Page 9 of 12
Preliminary Datasheet
Mar/07