Zxbm2004, Two phase variable speed motor control pre-driver, New prod uc t functional descriptions – Diodes ZXBM2004 User Manual
Page 6
ZXBM2004
TWO PHASE VARIABLE SPEED
MOTOR CONTROL PRE-DRIVER
ZXBM2004
Document number: DS33433 Rev. 5 - 2
6 of 19
February 2012
© Diodes Incorporated
NEW PROD
UC
T
Functional Descriptions
H+ and H- Hall Inputs
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 - Output Reference Voltage
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 current drawn from the pin by the minimum speed potential divider to pin S
MIN
and any voltage
setting network should not exceed 1mA in total at maximum temperature.
SPD - Speed Control Input
The voltage applied to the SPD pin provides control over motor speed by varying the Pulse Width Modulated (PWM) drive
ratio at the Ph1 and Ph2 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
– Minimum Speed Setting
A voltage can be set on S
MIN
pin via a potential divider between the ThRef and Gnd. This voltage is monitored by the SPD
pin such that internally SPD voltage cannot rise above S
MIN
voltage. 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 resistor greater than 1k
Ω should be placed in series with the SPD pin.
C
PWM
– Output PWM Frequency Setting
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:
(
)
(
)
PWMD
THL
THH
PWMC
THL
THH
PWM
I
C
V
V
I
C
V
V
T
Ч
−
+
Ч
−
=
Where: C = (C
PWM
+15) in pF
V
THH
and V
THL
are the C
PWM
pin threshold voltages
I
PWMC
and I
PWMD
are the charge and discharge currents in µA.
T
PWM
is in ms
As these threshold voltages are nominally set to V
THH
= 3V and V
THL
= 1V the equations can be simplified as follows:
PWMD
PWMC
PWM
I
C
2
I
C
2
T
+
=