left open) the motor rotates at full speed. When the PWM signal is “Low” the motor is
stopped (and the IC outputs are set to high-impedance). By changing the PWM duty cycle,
the speed can be adjusted. Notice that the PWM frequency has no special meaning for the
motor speed and is asynchronous with the activation of the output transistors. Thus the user
has maximum freedom to choose the PWM system frequency within a wide range (from
20KHz to 50kHz)
Frequency Generator Function
The Frequency Generator output (FG) is a “Hall-sensor equivalent” digital output, giving
information to an external controller about the speed and phase of the motor. When a lock
(or out-of-sync) situation is detected by the driver, this output is set to “Low” until the motor is
restarted. The FG pin is an open collector output, connecting to a logical voltage level
through an external pull-up resistor. Leave the pin open when not used.
Lockup Protection and Automatic Restart
If the motor is stopped (blocked) or if it loses synchronization with the driver, a lock-up
protection circuit detects this situation and disables the driver (by setting its outputs to
high-impedance) in order to prevent the motor coil from burnout. After a "release time" (LRT),
the lock-up protection is released and normal operation resumes for a given time (LDT). In
case of the motor is still blocked, a new period of waiting time is started. LRT and LDT
timings are fixed internally, so that no external capacitor is needed.
Figure 4 Lock and FG timing charts
Thermal Shutdown
The WT7062 has a thermal protection function which detects when the die temperature
exceeds Tj=150° When this temperature is reached, the circuit enters the thermal
C.
shutdown mode and the outputs U phase, V phase and W phase are disabled (high
impedance), avoiding IC destruction and allowing the circuit to cool down. Once the junction
temperature (TJ) has dropped below 120° the normal operation resumes (thermal
C,
detection circuit has 30° hysteresis function).
C
Weltrend Semiconductor, Inc.
Proprietary & Confidential
Mar. 4, 2011
Rev. 0.05
Page 5
WELTREND [ WELTREND SEMICONDUCTOR ]
