
As these threshold voltages are nominally setto V
=
3V and V
THL
= 1V the equations can be simplified as
follows:
T
C
2
I
C
2
I
PWM
PWMC
PWMD
=
+
C
LCK
- Locked rotor timing capacitor
Should the fan stop rotating for any reason, i.e. an
obstruction in the fan blade or a seized bearing, then
the device will enter a Rotor Locked condition. In this
condition aftera predetermined time(T
) theRD pin
will go high and the Phase outputs will be disabled.
After a further delay (T
) the controller will re-enable
the Phase drive fora defined period (T
) in an attempt
to re-start the fan. This cycle of (T
) and (T
ON
) will be
repeated indefinitely or until the fan re-starts.
GND - Ground
This is the device supply ground return pin and will
generally be the most negative supply pin to the fan.
RD - Locked Rotor error output
This pin is the Locked Rotor output as referred to in the
C
timing section above. It is high when the rotor is
stopped and low when it is running.
This is an open collector drive giving an active pull
down with the high level being provided by an external
pull up resistor.
FG - Frequency Generator (speed) output
This is the Frequency Generator output and is a
buffered signal from the Hall sensor.
This is an open collector drive giving an active pull
down with the high level being provided by an external
pull up resistor.
Ph1Lo & Ph2Lo - Driver
This pair of outputs drive the external devices. These
outputs provide both the commutation and PWM
waveforms. The outputs are of the Darlington emitter
follower type with an active pull-down to help faster
switch off when using bipolar devices. When in the
high state the outputs will provide up to 80mA of drive
into the base or gates of external transistors as shown
in the Typical Application circuit following.
When in the low state the active Phase drive is capable
of sinking up to 16mA when driving low to aid turn off
times during PWM operation. When the Phase is
inactive the outputis held low by an internal pull-down
resistor.
V+OP - Phase Outputs Supply Voltage
This pin is the supply to the Phase outputs and will be
connected differently dependant upon external
transistor type.
For bipolar devices this pin will be connected by a
resistor to the V
pin. The resistor is used to control
the current into the transistor base so its value is
chosen accordingly.
ForMOSFET devices the pin will connectdirectly to the
V
CC
pin.
ZXBM2004
S E M IC O N D U C T O R S
ISSUE 3 - MAY 2005
6