APPLICATION INFORMATION
Thissection gives a briefinsightintoapplicationsusing
the ZXBM200x series. More complete data is available
in the ZXBM200x Series Applications Note, visit
www.zetex.com/zxbm or contact your nearest Zetex
office for full details.
The ZXBM200x series of 2-phase DC brushless motor
pre-drivers are capable of driving both Bipolar or
MOSFET power transistors.
For smaller fans and blowers it is likely that bipolar
power transistors would be used as shown in the
following Applications circuit.
InFigure1,R1& R2 have theirvalueselectedtoprovide
suitable base current in keeping with the winding
currentandgainof the power transistorsQ1&Q2. R3 &
R4 have their value selected to provide efficient
switch-off of Q1 & Q2. The Zener diodes ZD1 & ZD2
provideactiveclampinginconjunctionwithQ1&Q2.
It is also recommended that the supply de-coupling
capacitor C3 is positioned asclose as is practical to the
ZXBM device pins.
In the case of higher power fans and blowers it maybe
more applicable to use MOSFET devices to switch the
windings as illustrated in the second applications
circuit shown in Figure 2.
In Figure 2, the Resistor ratio of R1 to R3 and R2 to R4
provide the required Gate turn-on voltage whilst the
absolute values will be chosen to provide sufficient
gate switching currents.
Also illustrated in the two Applications circuits above
are the methods of connection for both a ‘naked’ Hall
device, as seen in the bipolar circuit in Figure 1, and a
buffered Hall device, as in the MOSFET circuit in Figure
2.In this latter circuit R5 & R6 biastheH-pinatavoltage
equivalent to half the swing of the Hall device. R7 will
be needed if the buffered Hall device does not have its
own internal pull-up.
Graph 1 below, illustrates the PWM drive waveform
takenfromand application usingthe MOSFET circuitin
Figure 2. This shows the waveforms to be found at the
Ph1 output and at the drain/Winding node.
ZXBM2001
ZXBM2002 ZXBM2003
SEMICONDUCTORS
ISSUE 4 - OCTOBER 2004
8
