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ZXBM2004

TWO PHASE VARIABLE SPEED MOTOR CONTROL PRE-DRIVER

Diodes Incorporated. 

ZXBM2004

TWO PHASE VARIABLE SPEED

MOTOR CONTROL PRE-DRIVER

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 VCC. 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 SMIN 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.

SMIN – Minimum Speed Setting

A voltage can be set on SMIN 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 SMIN 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 1kΩ should be placed in series with the SPD pin.

CPWM – 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 CPWM timing period (TPWM) is determined by the following equation:

TPWM = (VTHH − VTHL)× C + (VTHH − VTHL)× C

IPWMC

IPWMD

Where: C = (CPWM +15) in pF

VTHH and VTHL are the CPWM pin threshold voltages

IPWMC and IPWMD are the charge and discharge currents in µA.

TPWM is in ms

As these threshold voltages are nominally set to VTHH = 3V and VTHL = 1V the equations can be simplified as follows:

TPWM = 2C + 2C

IPWMC IPWMD

ZXBM2004

Document number: DS33433 Rev. 5 - 2

6 of 19

www.diodes.com

February 2012

© Diodes Incorporated

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