Application examples

AN4232

12/17

DocID024134 Rev 2

2.4

Preventing false over-current detections in motor control

applications

Note:

The output blanking feature is only available on STM32F30x devices.

At PWM startup, a very high current flows through the current shunt during a short time and

may be seen by the comparator as greater than the inverting input. In this case, the

comparator output will be set and may generate an unwanted emergency stop if the

comparator is connected to the timer break input. This startup current is acceptable at the

beginning of PWM periods and must not be managed by the comparator as a fault current

(short-circuit, overload, ground fault, etc.)

In STM32F30x devices, the analog comparator output can be blanked using a timer output

as a blanking source. The blanking source is selected/configured by software and is ANDed

with the comparator output, resulting in a final comparator output which is not high during

the peaks at the beginning of the PWM periods.

Figure 7 shows how the comparator output is ANDed with a timer output in order to blank

the comparator output for a programmed duration. The same TIM as the one used for the

PWM generation can also be used for comparator blanking.

Figure 7. Comparator output blanking

An example code written in C language is available in the

Project\STM32F30x_StdPeriph_Examples\COMP\COMP_OutputBlanking folder in the

STM32F30x_DSP and standard peripherals library package stm32f30x_dsp_stdperiph_lib.

Note:

In STM32CubeF3 firmware package this example is available in the

Projects\STM32303C_EVAL\Examples\COMP\COMP_OutputBlanking and the

Projects\STM32303E_EVAL\Examples\COMP\COMP_OutputBlanking folders.