DC motor system IC TLE9560/61/62 - What is the cross-protection time for symmetrization for?
The cross-current protection (tccp) for symmetrization is applied during the PWM operating of a half-bridge while the active freewheeling is enabled:
At the rising edge of the PWM signal:
- the freewheeling (FW) MOSFET is turned off during the cross-current time for the FW MOSFET (tccp FW).
- when tccp FW is over, the active MOSFET is turned on, in order to avoid cross-conduction.
Therefore the turn-on of the active MOSFET is delayed by tccp FW.
At the falling edge of the PWM signal:
- the active MOSFET is kept on for tccp for symmetrization (= tccp FW) , in order to compensate delay at the PWM rising edge caused by tccp FW
- when tccp for symmetrization is over, the active MOSFET is turned off during the cross-current time for the active MOSFET (tccp active)
- when tccp active is over, the FW MOSFET is turned on, in order to avoid cross-conduction
To sum up: the tccp for symmetrization is applied to avoid a distortion between the duty cycle applied to the PWM pin and the effective duty cycle, caused by tccp fw.