點晶科技股份有限公司

SILICON TOUCH TECHNOLOGY INC.

ST1117A / ST1117B /ST1117C

SP-ST1117ABC-A.007

Version

：A.007

Page

：4

Application Notes

With low voltage start-up feature, the device is operated within wide supply

voltage range from 1.5 to 7.5 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 sink/drive” for V(HIN) = logic

low. Similarly, the output O1/O2 will be “turned to drive/sink” for V(HIN) =

logic high .

The FGR pin is an open-drained output. The output frequency is dividing the hall

switching frequency with 2 for ST1117A, the same frequency with hall switching

for ST1117B, and the rotating detection for ST1117C. 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. The PWM command

is active high. If low acoustic noise is desired, the PWM frequency range below

200Hz or 20KHz ~ 40KHz is recommended.

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.