L8150 datasheet(16/37 Pages) STMICROELECTRONICS

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Operating description

L8150

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Operating description

5.1

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:

●

FS signal;

●

SD (shut down) signal.

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):

Vo[V] = 5.617V - 0.909 · Vsp[V]

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.

5.2

Smooth Drive and Control logic description

Two basic driving techniques are applied according to different conditions:

●

rectangular driving

●

sinusoidal driving (Smooth Drive)

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 (Figure 5), where the synchronization control

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:

TMAX = 36*38656*Tck " 141.5 msec, with Tck = 101.7ns (Typical target value)

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