908E425 Datasheet, PDF (32/49 Pages) Freescale Semiconductor, Inc – Integrated Quad Half H-Bridge with Power Supply, Embedded MCU, and LIN Serial Communication

FUNCTIONAL DEVICE OPERATION
LOGIC COMMANDS AND REGISTERS
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
Coil1 Current
edge on the FGEN input. In step motor applications this
feature allows the reduction of EMI due to a reduction of the
di/dt (Figure 19).
Coil2 Current
FGEN Input
(MCU PWM
Signal)
Current in
VSUP Line
HB1
Coil1…..
HB2
HB3
Coil2…..
HB4
Figure 19. Offset Chopping for Step Motor Control
HALF-BRIDGE CURRENT RECOPY
Each low-side MOSFET has an additional sense output to
allow a current recopy feature. This sense source is internally
connected to a shunt resistor. The drop voltage is amplified
and switched to the analog multiplexer.
The factor for the current sense amplification can be
selected via bit CSA in the System Control Register.
• CSA = 1: Low resolution selected (500 mA
measurement range)
• CSA = 0: High resolution selected (2.5 A measurement
range)
HALF-BRIDGE BEMF GENERATION
The BEMF output is set to 1 if a recirculation current is
detected in any half-bridge. This recirculation current flows
via the two freewheeling diodes of the power MOSFETs. The
BEMF circuitry detects that and generates a HIGH on the
BEMF output as long as a recirculation current is detected.
This signal provides a flexible and reliable detection of stall in
step motor applications. For this the BEMF circuitry takes
advantage of the instability of the electrical and mechanical
behavior of a step motor when blocked. In addition the signal
can be used for open load detection (absence of this signal),
see Figure 20.
908E425
32
Analog Integrated Circuit Device Data
Freescale Semiconductor