Using The Break Function - ST STM32L4x6 Reference Manual

General-purpose timers (TIM15/16/17)
28.4.13

Using the break function

The purpose of the break function is to protect power switches driven by PWM signals
generated with the TIM15/16/17 timers. The break input is usually connected to fault outputs
of power stages and 3-phase inverters. When activated, the break circuitry shuts down the
PWM outputs and forces them to a predefined safe state.
The break channel gathers both system-level fault (clock failure, parity error,...) and
application fault (from input pins and built-in comparator), and can force the outputs to a
predefined level (either active or inactive) after a deadtime duration.
The output enable signal and output levels during break are depending on several control
bits:
• the MOE bit in TIMx_BDTR register allows to enable /disable the outputs by software
and is reset in case of break or break2 event.
•
the OSSI bit in the TIMx_BDTR register defines whether the timer controls the output in
inactive state or releases the control to the GPIO controller (typically to have it in Hi-Z
mode)
•
the OISx and OISxN bits in the TIMx_CR2 register which are setting the output shut-
down level, either active or inactive. The OCx and OCxN outputs cannot be set both to
active level at a given time, whatever the OISx and OISxN values. Refer to
Output control bits for complementary OCx and OCxN channels with break feature on
page 978
When exiting from reset, the break circuit is disabled and the MOE bit is low. The break
function is enabled by setting the BKE bit in the TIMx_BDTR register. The break input
polarity can be selected by configuring the BKP bit in the same register. BKE and BKP can
be modified at the same time. When the BKE and BKP bits are written, a delay of 1 APB
clock cycle is applied before the writing is effective. Consequently, it is necessary to wait 1
APB clock period to correctly read back the bit after the write operation.
Because MOE falling edge can be asynchronous, a resynchronization circuit has been
inserted between the actual signal (acting on the outputs) and the synchronous control bit
(accessed in the TIMx_BDTR register). It results in some delays between the asynchronous
and the synchronous signals. In particular, if you write MOE to 1 whereas it was low, you
must insert a delay (dummy instruction) before reading it correctly. This is because you write
the asynchronous signal and read the synchronous signal.
The break can be generated from multiple sources which can be individually enabled and
with programmable edge sensitivity, using the TIMx_OR2 register.
The sources for break (BRK) channel are:
• An external source connected to one of the BKIN pin (as per selection done in the
AFIO controller), with polarity selection and optional digital filtering
•
An internal source:
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954/1693
for more details.
®
– the Cortex -M4 LOCKUP output
– the PVD output
– the SRAM parity error signal
– a flash ECC error
– a clock failure event generated by the CSS detector
– the output from a comparator, with polarity selection and optional digital filtering
– the analog watchdog output of the DFSDM peripheral
DocID024597 Rev 3
RM0351
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