
Pin Functional Descriptions
1. VCC
- Applied voltage
Thisisthedevicesupplyvoltage.For5Vto12Vfansthis
canbesupplieddirectlyfromtheFanMotorsupply.For
fans likely to run in excess of the 18V maximum rating
for the device this will be supplied from an external
regulator such as a zener diode.
2. H+
3. H-
- Hall input
- Hall input
TherotorpositionoftheFanMotorisdetectedbyaHall
sensor whose output is applied to these pins. This
sensor can be either a 4 pin ‘naked’ Hall device or a 3
pin buffered switching type. For a 4 pin device the
differential Hall output signal is connected to the H+
and H- pins. For a 3 pin buffered Hall sensor the Hall
device output is attached to the H+ pin whilst the H- pin
has an external potential divider attached to hold the
pin at half V
CC
. When H+ is high in relation to H- Ph2 is
the active drive.
4. SPD
- Speed control voltage input
This pin provides control over the Fan Motor speed by
varying the Pulse Width Modulated (PWM) drive ratio
atthePh1andPh2outputs.Thiscontrolsignalcantake
the form of either a voltage input of nominal range 2V
to 1V, representing 0% to 100% drive respectively, or
alternatively a thermistor can be attached to this pin to
control the voltage. The pin has an internal potential
divider between Gnd and an internal 2.0V reference
designed to hold the pin at approximately 1.5V. This
willrepresentadriveofnominally50%.Theadditionof
a 100k NTC thermistor to ground, for example, will
provide a drive nominally 70% at 25°C and 100% at
50°C.
If speed control is not required this pin is can be left
open circuit for 50% drive or tied to ground by a 10k
resistor to provide 100% drive.
If required this pin can also be used as an enable pin.
The application of a voltage of 2.0V to V
CC
will to force
the PWM drive fully off, in effect disabling the drive.
5. GND
- Ground
This is the device supply ground return pin and will
generally be the most negative supply pin to the fan.
6. LOCK/FG
Frequency Generator (speed) output
- Locked Rotor error output /
On the ZXBM2001 the Lock/FG pin is designed to be a
dual function pin to provide an indication of the Fans
rotational speed together with an indication of when
the Fan has failed rotating for whatever reason (Rotor
Locked condition). The pin is an open collector drive,
that is there is an active pull down with the high level
being provided by an external pull up resistor. Under
correct operating conditions, and with this external
pull-up in place, this pin will provide an output signal
whose frequency will be twice that of the rotational
frequency of the fan. Should the fan itself 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 the Lock/FG pin will
go high (regardless of the state of the Hall sensor)
whentheC
LCK
pinreachestheV
THH
thresholdandwill
remain high until the fan blades start rotating again.
On the ZXBM2002 variant this pin is Lock. During
normal operation the signal will be low and during a
Locked Rotor condition the pin will go high when the
C
LCK
pin reaches the V
THH
threshold.
FortheZXBM2003variantthispinisFG.Thissignalisa
buffered and inverted output of the Hall signal and
therefore provides an output signal whose frequency
willbetwicethatoftherotationalfrequencyofthefan.
7. C
LCK
- Locked Rotor timing capacitor
When in a Locked Rotor condition as described above
thePh1andPh2driveoutputsgointoasafedrivemode
to protect the external drive devices and the motor
windings. This condition consists of driving the motor
for a short period then waiting for a longer period
before trying again. The frequency at which this takes
place is determined by the size of the capacitor applied
to this CLCK pin. For a 12V supply a value of 1.0uF will
typically provide an ‘On’ (drive) period of 0.33s and an
‘Off’(wait)periodof4.0s,givinganOn:Offratioof1:12.
ZXBM2001
ZXBM2002 ZXBM2003
ISSUE 1 - APRIL 2002
4