zxbm1015 Zetex Semiconductors plc., zxbm1015 Datasheet - Page 8

• Manufacturer Part Number: zxbm1015
• Description: Variable Speed Single-phase Bldc Motor Controller
• Manufacturer: Zetex Semiconductors plc.

V
This is the device internal circuitry supply voltage. For
5V to 12V fans this can be supplied directly from the Fan
Motor supply. For fans likely to run in excess of the 18V
maximum rating for the device this will be supplied
from an external regulator such as a Zener diode.
SetTh - Set Threshold Voltage
The ZXBM1015 contains a current monitor circuit used
to sense the current flowing in the motor winding and
this pin is used to control how the circuit responds to
that current.
The device works in a threshold feedback mode using a
potential divider to the Set Threshold pin. This
potential divider is used to set a voltage that will be
compared with the voltage generated by the current in
a Sense resistor attached in the Low-Side ground
return of the external H-Bridge driver. When the current
in the Sense resistor, and thus the voltage, rises above
the SetTh pin threshold the controller will back-off the
PWM drive to limit the maximum current taken by the
motor. To do this the current monitor will internally
apply a correction signal to the SPD pin. If the motor
current is below the set threshold the controller does
not influence the SPD voltage. A suitable voltage range
for the SetTh pin, and thus the sensed voltage on the
Sense pin, would be 50mV to 200mV.
ZXBM1015
CC
- Applied Voltage
8
It should be noted that the effectiveness of the control is
determined by the external network used to control the
SPD pin. It will not work where the fan is being
controlled by a low source impedance voltage. If the
fan is being controlled from an external voltage source
then a resistor >1k should be placed in series with the
SPD pin.
The minimum speed setting on the SMIN pin will
override the current limit feature. A current cannot be
set that is lower than the current taken when the motor
stalls at minimum speed.
Sense
This pin is used by the current sensing circuit, as
described above, to monitor the current taken by the
motor windings. The signal comes from a sense
resistor in the Low-Side ground return of the external
H-Bridge driver.
ISSUE 3 - MAY 2007