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AMIS30512C5122G Datasheet, PDF (10/30 Pages) ON Semiconductor – Micro-Stepping Motor Driver | |||
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AMISâ30512
Functional Description
HâBridge Drivers
A full Hâbridge is integrated for each of the two stator
windings. Each Hâbridge consists of two lowâside and two
highâside Nâtype MOSFET switches. Writing logic â0â in
bit <MOTEN> disables all drivers (highâimpedance).
Writing logic â1â in this bit enables both bridges and current
can flow in the motor stator windings.
In order to avoid large currents through the Hâbridge
switches, it is guaranteed that the topâ and bottomâswitches
of the same halfâbridge are never conductive
simultaneously (interlock delay).
A twoâstage protection against shorts on motor lines is
implemented. In a first stage, the current in the driver is
limited. Secondly, when excessive voltage is sensed across
the transistor, the transistor is switchedâoff.
In order to reduce the radiated/conducted emission,
voltage slope control is implemented in the output switches.
The output slope is defined by the gateâdrain capacitance of
output transistor and the (limited) current that drives the
gate. There are two trimming bits for slope control
(Table 25: SPI Control Parameter Overview EMC[1:0]).
The power transistors are equipped with soâcalled âactive
diodesâ: when a current is forced through the transistor
switch in the reverse direction, i.e. from source to drain, then
the transistor is switched on. This ensures that most of the
current flows through the channel of the transistor instead of
through the inherent parasitic drainâbulk diode.
Depending on the desired current range and the
microâstep position at hand, the Rdson of the lowâside
transistors will be adapted such that excellent currentâsense
accuracy is maintained. The Rdson of the highâside
transistors remain unchanged, see Table 4: DC Parameters
for more details.
PWM Current Control
A PWM comparator compares continuously the actual
winding current with the requested current and feeds back
the information to a digital regulation loop. This loop then
generates a PWM signal, which turns on/off the Hâbridge
switches. The switching points of the PWM dutyâcycle are
synchronized to the onâchip PWM clock. The frequency of
the PWM controller can be doubled and an artificial jitter
can be added (Table 14: SPI Control Register 1). The PWM
frequency will not vary with changes in the supply voltage.
Also variations in motorâspeed or loadâconditions of the
motor have no effect. There are no external components
required to adjust the PWM frequency.
Automatic Forward and SlowâFast Decay
The PWM generation is in steadyâstate using a
combination of forward and slowâdecay. The absence of
fastâdecay in this mode, guarantees the lowest possible
currentâripple âby designâ. For transients to lower current
levels, fastâdecay is automatically activated to allow
highâspeed response. The selection of fast or slow decay is
completely transparent for the user and no additional
parameters are required for operation.
Icoil
Set value
0
TPWM
Actual value
t
Forward & Slow Decay
Fast Decay & Forward
Forward & Slow Decay
Figure 7. Forward and Slow/Fast Decay PWM
In case the supply voltage is lower than 2*Bemf, then the
duty cycle of the PWM is adapted automatically to >50% to
maintain the requested average current in the coils. This
process is completely automatic and requires no additional
parameters for operation. The overâall currentâripple is
divided by two if PWM frequency is doubled (Table 14: SPI
Control Register 1).
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