Diodes ZXBM1015 - Manual (Page 7)

As these threshold voltages are nominally set to V THH
= 3V and V THL = 1V the equations can be simplified as
follows:
t
C
I
C
I
PWM
PWMC PWMD
= +
2 2
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 after a predetermined time (t
lock ) the RD pin
will go high and the Phase outputs will be disabled.
After a further delay (t
off ) the controller will re-enable
the Phase drive for a defined period ((t on ) in an attempt
to re-start the fan. This cycle of (t off ) and (t on ) will be
repeated indefinitely or until the fan re-starts.
The frequency at which this takes place is determined
by the value of the capacitor applied to this C
LCK pin.
For a 12V supply a value of 1uF will typically provide an
'On' (drive) period of 0.56s and an 'Off' (wait) period of
6.8s, giving an On:Off ratio of 1:12.
The C LCK timing periods are determined by the
following equations:
t
V x C
I
lock
THH LCK
LCKC
=
t
V V x C
I
on
THH THL LCK
LCKC
=
− ( )
t
V V x C
I
off
THH THL LCK
LCKD
=
− ( )
Where: V THH and V THL are the C LCK pin
threshold voltages and
I
LCKC and I LCKD are the charge and
discharge currents.
As these threshold voltages are nominally set to V THH
= 3V and V THL = 1V the equations can be simplified as
follows:
t
x C
I
lock
LCK
LCKC
=
3
t
xC
I
on
LCK
LCKC
=
2
t
x C
I off
LCK
LCKC
=
2
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
LCK 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)
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 - Low-side External H-bridge Driver
These pair of outputs drive the Low side of the external
high power H-bridge devices that in turn drives the
single phase winding. 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 or MOSFET devices with a high gate
capacitance. 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 32mA when driving low to aid turn off
times during PWM operation. When the Phase is
inactive the output is held low by a 7.5k
⍀ internal
pull-down resistor.
Ph1Hi & Ph2Hi - High-side External H-bridge Driver
These are the High side outputs to the external
H-bridge and are open collector outputs capable of
sinking 100mA. This signal provides commutation only
to the H-bridge.
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 via a
resistor to the VCC pin. The resistor is used to control
the current into the transistor base so its value is
chosen accordingly.
For MOSFET devices the pin will connect directly to the
VCC pin
ZXBM1015
ISSUE 3 - MAY 2007
7