AN3248

PWM signal control

Doc ID 17758 Rev 3

11/17

4

PWM signal control

In STM32L1 devices, the COMP2 output can be redirected to the output compare reference

clear signal (OCREFCLR) of the embedded timers: TIM2, TIM3, and TIM4 (refer to Figure 7:

COMP2 with output redirection feature). The possibility of redirecting the COMP2 output can

be used to provide a fast response time that is independent from the system frequency

when an analog event occurs. This application case controls a PWM signal for motor control

when the current sensor output is connected to the COMP2 non-inverting input. In this

situation, the reference voltage is connected to the COMP2 inverting input. When the

current sensor output exceeds the selected threshold, the COMP2 output goes high and the

PWM signals switch to safe state.

Figure 9.

PWM signal control: COMP2 output redirection to timer

1.

In the pulse width measurement application, COMP1 cannot be used since its output CMP1OUT (internal

output) is not connected to the embedded timers.

Note:

When the current sensor voltage reaches the reference voltage, the COMP2 output goes

high. Consequently, the PWM and output compare reference signals go low (to safe state).

Time

PWM signal

Time

PWM signal at safe state (low level)

Time

COMP2 output is at high level

Low level

High level

COMP2 output

Current sensor output

Reference voltage

ai18708