Application examples

AN4232

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Application examples

This section describes how the analog comparators embedded in STM32F30x and

STM32F37x devices can be used in applicative examples such as humidity measurement,

cycle-by-cycle motor control, voltage monitoring, and PWM control.

2.1

Cycle-by-cycle current control (peak current control)

Cycle-by-cycle current control (also called peak current control) is a technique broadly used

for power conversion, typically for DC-DC converters, lighting or motor drives.

The current sensor output (for instance a shunt or a current transformer) is connected to the

on the inverting input (either a simple resistor divider or the embedded DAC if the set-point

has to be adjusted dynamically). When the monitored current exceeds the current limit, the

comparator output goes high and disables the PWM outputs for the remaining time in the

PWM cycle. On the next cycle, if the comparator output is back to zero (i.e. the current is

below the limit), the PWM output is enabled again.

As displayed in Figure 4, STM32F30x and STM32F37x devices are designed for these

kinds of applications, where the timer can be used in PWM mode to control the motor. The

analog comparator can be used to monitor the motor current on-the-fly. The comparator

output can be internally redirected to the OCREFCLR signal which controls the PWM state.

The embedded Digital Analog Converter can be internally connected to the inverting input of

the comparator.

In Figure 4. both the real PWM (solid line) and the programmed PWM (dotted line) values (if

there were no OCrefClr feedback) are displayed.