Diodes ZXBM2003 - Manual (Page 6)

Locked Rotor timing capacitor (CONT).
As these threshold voltages are nominally set to
V
THH
=2V and V
THL
=1V the equations can be simplified
as follows:
T
C
I
LCK
LCKC
lock
=
× 2
T =
C
I
on
LCK
LCKC
T
C
I
LCK
LCKD
off
=
8. C
PWM
- Sets PWM frequency
- external PWM input
This pin has an external capacitor attached to set the
PWM frequency for the Phase drive outputs. A
capacitor value of 0.15nF will provide a PWM
frequency of typically 24kHz.
The C
LCK
timing period (T
pwm
) is determined by the
following equation:
T =
(V - V ) C
I
(V V ) C
I
lock
THH THL
PWMC
THH THL
PWMD
Ч
+
− Ч
Where T PWM is in ␮s
C = C
PWM
+15 in pF
I PWM & I PWMD are in ␮A
Where V
THH
and V
THL
are the C
PWM
pin threshold
voltages and I PWMC and I PWMD are the charge and
discharge currents.
As these threshold voltages are nominally set to
V
THH =2V and V THL =1V the equations can be simplified
as follows:
T
C
I
C
I
PWM
PWMC PWMD
= +
The C
PWM
pin can also be used as in input for an
externally derived PWM signal to control the motor
speed. The signal should have a VOL <1V and a VOH
>2V. A standard TTL or CMOS digital signal is ideal.
When driving from an external PWM source no
capacitor should be attached to the C
PWM
pin and the
SPD pin should be left open circuit.
9. PH2 - External transistor driver
10. PH1 - External transistor driver
These are the Phase drive outputs and are open
darlington emitter followers designed to provide up to
80mA of drive to external transistors as shown in the
Application circuits following. The external transistors
in turn drive the fan motor windings.
ZXBM2001
ZXBM2002 ZXBM2003
S E M I C O N D U C T O R S
ISSUE 4 - OCTOBER 2004
6