XC886/888CLM
Capture/Compare Unit 6
User’s Manual
14-8
V1.3, 2010-02
CCU6, V 1.0
For the hysteresis-like compare mode (MSEL6x = 1001
B
) (see
), the
setting of the compare state bit is possible only while the corresponding input
CCPOSx = 1 (inactive).
If the hall sensor mode (MSEL6x = 1000
B
) is selected (see
compare state bits of the compare channels 1 and 2 are modified by the timer T12 in
order to indicate that a programmed time interval has elapsed.
The set is only generated when bit CC6xST is reset; a reset can only take place when
the bit is set. Thus, the events triggering the set and reset actions of the CC6xST bit must
be combined. This OR-combination of the resulting set and reset permits the reload of
the dead-time counter to be triggered (see
). This is triggered only if bit
CC6xST is changed, permitting a correct PWM generation with dead-time and the
complete duty cycle range of 0% to 100% in edge-aligned and center-aligned modes.
14.1.1.5
Duty Cycle of 0% and 100%
These counting and switching rules ensure a PWM functionality in the full range between
0% and 100% duty cycle (duty cycle = active time/total PWM period). In order to obtain
a duty cycle of 0% (compare state never active), a compare value of T12P+1 must be
programmed (for both compare modes). A compare value of 0 will lead to a duty cycle
of 100% (compare state always active).
14.1.1.6
Dead-time Generation
In most cases, the switching behavior of the connected power switches is not
symmetrical with respect to the times needed to switch on and to switch off. A general
problem arises if the time taken to switch on is less than the time to switch off the power
device. This leads to a short-circuit in the inverter bridge leg, which may damage the
entire system. In order to solve this problem by hardware, the CCU6 contains a
programmable dead-time counter, which delays the passive to active edge of the
switching signals (the active to passive edge is not delayed).
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