st1117a Silicon Touch Technology Inc., st1117a Datasheet - Page 5

• Manufacturer Part Number: st1117a
• Description: Single Coil Brushless Dc Motor Drivers
• Manufacturer: Silicon Touch Technology Inc.

Application Notes
Single Coil Brushless DC Motor Drivers
The device is operated within wide supply voltage range from 1.5 to 8.5 Volts. The design,
specifications and performance have been optimized for 3V and 5V brushless DC motor
applications.
The output driver node O1/O2 will be “turned to drive/sink” when V(HP) > V(HN). Similarly,
the output O1/O2 will be “turned to sink/drive” when V(HP) < V(HN).
The output frequency on FGR pin is dividing the hall switching frequency with 2 for ST1117A
(-P,-M), the same frequency with hall switching for ST1117B (-P,-M), and the rotating
detection for ST1117C (-P,-M). With suitable pull up, the fan tachometer output can be used
directly with bipolar or MOS logic for motor speed monitoring/control. To get better FG signal
output, increasing stability of power system is required.
The pull up resistor about 20KΩ is connected to PWM pin already. The PWM command is
active high. If low acoustic noise is desired, the external PWM frequency is recommended
below 200Hz or 20KHz ~ 40KHz.
There is no need of external timing capacitor for lock protection and auto-restart function. For
5V application, the drivers will be shut down roughly 1 to 3 seconds after the motor is locked.
When the drivers have been shut down, the automatic self-restart circuit will try to power up
the drivers every 1 to 3 seconds until lock is released.
There is no requirement of protection diode for power reverse fault in normal applications. The
power polarity reverse protection circuit is built-in.
The capacitor between two ends of coil ( *3 in application circuit) is proposed to connect 0.1μF
for PWM application and 1μF for full-speed application.
The connection of the capacitor or Zener Diode (*1 in application circuit) between VDD and
GND, the capacitor (*2 in application circuit) between two Hall sensor output and the
capacitor (*3 in application circuit) between two ends of coil will increase system stability
when motor is rotating.
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Version：A.013
ST1117A/ST1117B/ST1117C
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