Zxbm1021, Functional descriptions – Diodes ZXBM1021 User Manual
Page 7
ZXBM1021
Document number: DS36322 Rev. 2 - 2
7 of 25
April 2014
© Diodes Incorporated
ZXBM1021
Functional Descriptions
H-Bias
– Hall Bias Output
This is a 1.75V nominal voltage source to bias a differential un-buffered Hall element sensor. If a Hall element requires a lower voltage than the
H-Bias output, connect an appropriate value resistor between the H-Bias pin and the Hall element supply pin.
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
ThRef
. When H+ is high in relation to H-, Ph2 is the active drive.
ThRef
– Output Reference Voltage
This is a 5V nominal reference output voltage. It is designed to 'source' current and therefore it will not 'sink' any current from a higher voltage.
The total current drawn from the ThRef pin by any external circuitry, such as the minimum speed potential divider to S
MIN
pin, should not exceed
10mA.
SPD
–Speed Control DC Voltage 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 variable DC voltage input of range 3V to 1V, representing 0% to 100% drive
respectively.
If variable speed control is not required this pin can be tied to 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 on this pin will force the PWM drive fully off, in effect
disabling the drive, providing the minimum speed function is not active (see S
MIN
pin section below).
1 in typical
application circuit for DC control in page 2) between speed control DC voltage input source and SPD pin.
PWMSPD
– Speed Control PWM Signal Input
The duty ratio of the speed control PWM signal input to this pin controls the fan motor speed by varying the output drive PWM ratio at the Ph1Lo
and Ph2Lo outputs. In the PWM speed control mode, the PWMSPD pin and the C
SPD
pin work together to the control the speed. The PWM
signal input on the PWMSPD pin is integrated by the capacitor on the C
SPD
pin (See C
SPD
pin description). PWM control input signal to the
PWMSPD pin needs to be a TTL logic levels.
C
SPD
– PWM Speed Control Signal Integrator Output
When PWM input signal is used to control the motor speed, PWM signal is integrated to DC voltage between 1V to 3V to for speed control. If
PWMSPD pin input is TTL low, the output voltage on C
SPD
is 3V and if PWMSPD pin is TTL high, the C
SPD
pin output is at 1V. In order for the
nput PWM frequency
applied to the PWMSPD input.
In PWM speed control mode,
SPD
pin to ground and connect C
SPD
pin to SPD pin. When in DC voltage speed
control mode keep PWMSPD and C
SPD
pins unconnected.
S
MIN
– Minimum Speed Setting
A voltage can be set on this pin via a potential divider between the ThRef and GND pins. This voltage is monitored by the SPD pin to clamp the
SPD control voltage so that it does not rise above S
MIN
voltage. As a higher voltage on the SPD pin represents a lower speed, the S
MIN
setting
prevents the motor speed going lower than the minimum speed set by the S
MIN
pin. 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 the minimum