NCV70514_16 Datasheet, PDF (11/31 Pages) ON Semiconductor – Micro-stepping Motor Driver

NCV70514
DETAILED OPERATING DESCRIPTION
H−Bridge Drivers with PWM Control
Two H−bridges are integrated to drive a bipolar stepper
motor. Each H−bridge consists of two low−side N−type
MOSFET switches and two high−side P−type MOSFET
switches. One PWM current control loop with on−chip
current sensing is implemented for each H−bridge.
Depending on the desired current range and the micro−step
position at hand, the R_DS(on) of the low−side transistors will
be adapted to maintain current−sense accuracy. A
comparator compares continuously the actual winding
current with the requested current and feeds back the
information to generate a PWM signal, which turns on/off
the H−bridge switches. The switching points of the PWM
duty−cycle are synchronized to the on−chip PWM clock. For
each output bridge the PWM duty cycle is measured and
stored in two appropriate status registers of the motor
controller.
The PWM frequency will not vary with changes in the
supply voltage. Also variations in motor−speed or load−
conditions of the motor have no effect. There are no external
components required to adjust the PWM frequency. In order
to avoid large currents through the H−bridge switches, it is
guaranteed that the top− and bottom−switches of the same
half−bridge are never conductive simultaneously (interlock
delay).
In order to reduce the radiated/conducted emission,
voltage slope control is implemented in the output switches.
Two bits in SPI control register 3 allow adjustment of the
voltage slopes.
A protection against shorts on motor lines is implemented.
When excessive voltage is sensed across a MOSFET for a
time longer than the required transition time, then the
MOSFET is switched−off.
Motor Enable−Disable
The H−bridges and PWM control can be disabled
(high−impedance state) by means of a bit <MOTEN> in the
SPI control registers. <MOTEN>=0 will only disable the
drivers and will not impact the functions of NXT, DIR,
RHB, SPI bus, etc. The H−bridges will resume normal PWM
operation by writing <MOTEN>=1 in the SPI register.
PWM current control is then enabled again and will regulate
current in both coils corresponding with the position given
by the current translator.
Automatic Forward and Slow−Fast Decay
The PWM generation is in steady−state using a
combination of forward and slow−decay. For transition to
lower current levels, fast−decay is automatically activated to
allow high−speed 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
t_pwm
Actual value
t
Forward & Slow Decay
Fast Decay & Forward
Forward & Slow Decay
Figure 7. Forward and Slow/Fast Decay PWM
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