STM32L4 Analog Comp
Hello, and welcome to this presentation of the STM32L4
comparators. It covers the main features of the ultra-lowpower comparators and some application examples.
1
The two comparators inside STM32 microcontroller provide
a binary output which indicates if the analog voltage on the
plus input is larger than the voltage on the negative input. It
allows the MCU to react when the analog signal crosses a
predefined threshold. The comparator continuously monitors
voltage in contrast to an analog-to-digital converter which
operates in sampled mode.
The comparator can be used to wake up devices from Sleep,
Low-power sleep and Stop modes.
Applications can benefit from the flexible configuration of
comparator properties which can be locked for safety
reasons. Another safety feature of comparator is its ability to
generate a break signal for timers allowing to safely stop the
generation of PWM driving signals.
2
The two integrated comparators can be combined into a
single window comparator.
The analog properties of the comparator include hysteresis
or a trade-off between speed and power consumption are
configurable.
It offers flexible inter-connections of inputs and outputs
allowing a threshold selection of several external and
internal inputs such as DAC outputs or internal reference
voltage outputs.
The comparator output can be connected to I/Os using the
alternate function channels or internally redirected to a
variety of timer inputs such as enabling the break event for
fast PWM shutdown. The user can create cycle-by-cycle
current control or input captures for timing measurements.
3
This slide shows the general block diagram of the
comparator integrated in the device.
4
The comparators’ power consumption can be adjusted to
have the optimum trade-off between the speed and energy
efficiency for a given application.
There are three modes available: high speed, medium speed
and ultra-low-power. The high speed mode would be
preferred for power conversion applications - for example, a
motor control design. While ultra-low power mode would be
the right choice for battery-powered applications where
reaction times are not critical - for example in PIR sensor
monitoring.
The comparator can stay active even if the rest of the
system is suspended and the clock is switched off.
5
The comparator can trigger an interrupt on the rising, falling
or both edges of the comparator output through the EXTI
line.
The on-chip comparator remains active and can be used to
wake up the device from all low-power modes except
Standby and Shutdown.
The on-chip comparator configuration capability allows the
user to select the best performance point for the targeted
application. It replaces the external stand-alone comparator,
thereby reducing the bill of materials.
8
The purpose of the window comparator is to trigger an
interrupt if the analog voltage goes beyond the defined lower
and upper voltage thresholds applied to the inverting inputs
of each comparator. This event can generate an interrupt
through the EXTI line. Two non-inverting inputs can be
connected internally by enabling the WINMODE bit and
therefore save one IO for another purpose.
9
Comparator output values can generate break input signals
for the timers on input pins using GPIO alternate function
selections incorporating the I/O open drain connection. The
purpose of the break function is to protect power switches
driven by PWM signals generated by timers. The two break
inputs are 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. Please see the timer training slides for
more details.
10
The comparator can be used in the cycle-by-cycle regulation
loop for monitoring the peak value of the current flowing into
the load. The purpose of the blanking function is to prevent
incorrect current regulation tripping due to short duration
current spikes at the beginning of the PWM period. Short
current spikes caused by activating the power switches can
produce false pulses on the comparator output – marked by
the blue color on the diagram. These pulses need to be
masked by a blanking window to avoid false fault detection.
The blanking window waveform can be generated by one of
the timer output channels.
11
Both comparators have identical electrical parameters and
configuration options. The difference in input
interconnections are summarized in this table. For the
difference in output redirections, please refer to product
datasheet.
This is a list of peripherals related to the comparators.
Please refer to these peripheral trainings for more
information if needed.
Thank you.
13
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