Diodes ZXBM1004 - Manual (Page 5)

PIN FUNCTIONAL DESCRIPTION
H+ - Hall input
H- - Hall input
The rotor position is detected by a Hall sensor, with the
output applied to the H+ and H- pins. This sensor can be
either a 4 pin 'naked' Hall device or of the 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
buffered Hall sensor the Hall device output is attached
to the H+ pin, with a pull-up attached if needed, 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.
ThRef - Network Reference
This is a reference voltage of nominal 3V. It is designed
for the ability to 'source' and therefore it will not 'sink'
any current from a higher voltage.
The total current drawn from the pin by the minimum
speed potential divider to pin S
MIN
and any voltage
setting network should not exceed 1mA at maximum
temperature.
SPD - Speed Control Input
The voltage applied to the SPD pin provides control
over the Fan Motor speed by varying the Pulse Width
Modulated (PWM) drive ratio at the Ph1Lo and Ph2Lo
outputs. The control signal takes the form of a voltage
input of range 3V to 1V, representing 0% to 100% drive
respectively.
If variable speed control is not required this pin can be
left with an external potential divider to set a fixed
speed or tied to ground to provide full speed i.e. 100%
PWM drive.
If required this pin can also be used as an enable pin.
The application of a voltage >3.0V will force the PWM
drive fully off, in effect disabling the drive.
S
MIN
- Sets Minimum Speed
A voltage can be set on this pin via a potential divider
between the ThRef and Gnd. This voltage is monitored
by the SPD pin such that it cannot rise above it. As a
higher voltage on the SPD pin represents a lower speed
it therefore restricts the lower speed range of the fan. If
this feature is not required the pin is left tied to ThRef so
no minimum speed will be set.
If the fan is being controlled from an external voltage
source onto the SPD pin then either this feature should
not be used or if it is required then a >1k
⍀ resistor
should be placed in series with the SPD pin.
C
PWM
- Sets PWM Frequency
This pin has an external capacitor attached to set the
PWM frequency for the Phase drive outputs. A
capacitor value of 0.1nF will provide a PWM frequency
of typically 24kHz.
The C
PWM
timing period (T
PWM
) is determined by the
following equation:
T
V V x C
I
V V x C
I
PWM
THH THL
PWMC
THH THL
PWMD
=
−
+
− ( ) ( )
Where: C = C
PWM
+15, in pF
V
T H H
a n d V
T H L
a r e t h e C
P W M
p i n
threshold voltages
I
PWMC
and I
PWMD
are the charge and
discharge currents in ␮A.
T
PWM
is in ms
ZXBM1004
S E M I C O N D U C T O R S
ISSUE 6 - MAY 2007
5