ZXBM2004  
					PIN FUNCTIONAL DESCRIPTION  
					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.  
					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 Vcc. When H+ is high in relation to  
					H-, Ph2 is the active drive.  
					SMIN - Sets Minim um Speed  
					A voltage can be set on this pin via a potential divider  
					between the ThRef and Gnd. This voltage is m onitored  
					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 m inim um 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.  
					ThRef - Netw ork Reference  
					This is a reference voltage of nom inal 3V. It is designed  
					for the ability to 'source' and therefore it will not 'sink'  
					any current from a higher voltage.  
					CPWM - Sets PWM Frequency  
					The total current drawn from the pin by the m inim um  
					speed potential divider to pin SMIN and any voltage  
					setting network should not exceed 1m A at m axim um  
					tem perature.  
					This pin has an external capacitor attached to set the  
					PWM fre q u e n cy fo r th e Ph a s e d rive o u tp u ts . A  
					capacitor value of 0.1nF will provide a PWM frequency  
					of typically 24kHz.  
					The CPWM tim ing period (TPWM) is determ ined by the  
					following equation:  
					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.  
					(VTHH − VTHL) x C (VTHH − VTHL) x C  
					TPWM  
					=
					+
					IPWMC  
					IPWMD  
					Where:  
					C = CPWM +15, in pF  
					VTHH a n d VTHL a r e t h e CP W M p in  
					threshold voltages  
					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.  
					IPWMC and IPWMD are the charge and  
					discharge currents in A.  
					TPWM is in m s  
					ISSUE 1 - OCTOBER 2004  
					5
					S E M IC O N D U C T O R S