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908E626 Datasheet, PDF (24/38 Pages) Freescale Semiconductor, Inc – Integrated Stepper Motor Driver with Embedded MCU and LIN Serial Communication
FUNCTIONAL DEVICE OPERATION
LOGIC COMMANDS AND REGISTERS
• 0 = High-side MOSFET turned on for half-bridge output
x.
HALF-BRIDGE CURRENT LIMITATION
Each low-side MOSFET offers a current limit or constant
current feature. This features is realized by a pulse width
modulation on the low-side MOSFET. The pulse width
modulation on the outputs is controlled by the FGEN input
and the load characteristics. The FGEN input provides the
PWM frequency, whereas the duty cycle is controlled by the
load characteristics.
Coil Current
The recommended frequency range for the FGEN and the
PWM is 0.1 kHz to 20 kHz.
Functionality
Each low-side MOSFET switches off if a current above the
selected current limit was detected. The 908E626 offers five
different current limits (refer to Table 5, page 27, for current
limit values). The low-side MOSFET switches on again if a
rising edge on the FGEN input was detected (Figure 12).
H-Bridge low-side
MOSFET will be switched
off if select current limit is
reached.
Half-Bridge
Low-Side Output
H-Bridge low-side
MOSFET will be turned on
with each rising edge of
the FGEN input.
t (µs)
FGEN Input
(MCU PWM
Signal)
t (µs)
Minimum 50 µs
t (µs)
Figure 12. Half-Bridge Current Limitation
Offset Chopping
If bit OFC_EN in the H-Bridge Control Register (HBCTL) is
set, HB1 and HB2 will continue to switch on the low-side
MOSFETs with the rising edge of the FGEN signal and HB3
and HB4 will switch on the low-side MOSFETs with the falling
edge on the FGEN input. In step motor applications, this
908E626
24
Analog Integrated Circuit Device Data
Freescale Semiconductor