E-L8150 STMICROELECTRONICS [STMicroelectronics], E-L8150 Datasheet - Page 16

• Manufacturer Part Number: E-L8150
• Description: Brushless motor predriver
• Manufacturer: STMICROELECTRONICS [STMicroelectronics]

Operating description
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5.1
5.2
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Operating description
Free-Run (FS) and Reset (SD) functions
This device does not have an actual startup signal, the working or standby condition
depends on two internally-generated signals:
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The first one (FS) is related to the Vsp external signal in the following way. Given the transfer
function of the INTAMP network shown below, which is obtained from the suggested INTamp
feedback network (see note 6 on Electrical characteristics section):
we have that when Vsp=1.23V, Vo equals to 4.5V; this signal (amplifier output) is fed to a
comparator (FScomp) whose threshold is set at 4.5V (plus some hysteresis). When Vo is
greater than 4.5V the device is in the so called "free running" mode, that is all the power
outputs are in high impedance; when the threshold is crossed the logic signal FS
commutates from High to Low, thus enabling normal device operation.
The second one (SD) switches from High to Low, thus enabling normal device operation.
When SD is High it acts as a reset signal for the whole logic block and as a stand-by signal
for the system oscillator and the speed amplifier. SD = High is generated by a low voltage
condition on VREG.
Smooth Drive and Control logic description
Two basic driving techniques are applied according to different conditions:
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The first one is used during startup phase or when the motor is rotating in the opposite
direction with respect to FR signal or T>TMAX, while Smooth Drive is used in normal
operation.
If a DC brushless motor has BEMF voltage with a sinusoidal-like shape, also the currents in
the windings are sinusoidal-like, if the applied voltage is sinusoidal. This means that the
torque is almost constant and the ripple is very small, allowing acoustic noise reduction and
lower EMI.
Smooth Drive basically applies three voltage patterns to the motor windings, each 120
electrical degrees out of phase with respect to the other, taking as reference the period
measured during the last electrical period. In order to do this, an internal 16-bit counter
(Period counter) is provided which is triggered (current value is stored in a register and the
counter is reset) at every rising edge of signal coming from U phase Hall sensor (HallU).
This kind of behavior is sketched in the picture
is represented by HallU rising edge.
The clock of the counter is the system clock (Fsys) divided by 36: this results in a maximum
value of the electrical period that the device can measure and consequently a minimum
speed at which Smooth Drive can work; this maximum period is:
FS signal;
SD (shut down) signal.
rectangular driving
sinusoidal driving (Smooth Drive)
TMAX = 36*38656*Tck " 141.5 msec, with Tck = 101.7ns (Typical target value)
Vo[V] = 5.617V - 0.909 · Vsp[V]
(Figure
5), where the synchronization control
L8150