PIN FUNCTIONAL DESCRIPTION

H+ - Positive Hall input

H- - Negative 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 Vcc. When H+ is high in relation to

H-, Ph2 is the active drive.

H-Bias- Hall Bias Output

This is a 1.75V nominal voltage source to bias a differential

unbufferred Hall sensor when that type is used.

ThRef - Network Reference

This is a reference voltage of nominal 5V and is used by

external networks to set up the SPD and SMIN pins

control voltages.

It is designed for the ability to 'source' current 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 on the SPD pin should not

exceed 10mA in total.

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.

The advantage of a fixed potential divider is so that the

benefit of the current control can be achieved.

If required this pin can also be used as a disable pin.

The application of a voltage >3.0V will force the PWM

drive fully off, in effect disabling the drive.

SMIN - 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 the SPD voltage cannot rise

above the 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 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.

ComDel - Adjusts the Commutation Delay

The ZXBM1017 has a fixed internal commutation delay

of 100us, however, there may be cases where this

needs to be adjusted to a different value. A resistor can

be attached to this pin to enable the delay to be

lengthened or shortened dependant upon application.

A resistor applied between the ComDel pin and Gnd

will lengthen the delay and a resistor applied between

the ComDel pin and ThRef will shorthen the delay. The

following Table indicates the delay expected for a

given resistor value.

Typical Commutation Delay

Resistor to

ThRef

Resistor to Gnd

Delay ( s)

100k

-28

220k

-40

--

80

-

470k

120

-

300k

168

CPWM - 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 CPWM timing period (tPWM) is determined by the

following equation:

t

VV

x C

I

VV

x C

I

PWM

THH

THL

PWMC

THH

THL

PWMD

=

−

+

−

()

()

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

A.

tPWM is in s

ZXBM1017

ISSUE 4 - MAY 2007

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