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In half-bridge applications where all power switches are modulated at the PWM frequency at all times, the power switches normally require more time to turn off than to turn on. If both the upper and lower power switches are switched at the same time (one turned on and the other turned off), both switches may be on for a short period of time until one switch completely turns off.
During this brief interval, a very high current (shoot-through current) may flow through both power switches, shorting the bridge supply. To avoid this potentially destructive shoot-through current from flowing during switching, turning on either of the power switches is normally delayed to allow the other switch to completely turn off when read code of chip.
In the Half-Bridge Output mode, a digitally programmable dead-band delay is available to avoid shoot-through current from destroying the bridge power switches in the process of MCU Recovering. The delay occurs at the signal transition from the nonactive state to the active state. See Figure 16-4 for illustration. Bits PDC6:PDC0 of the PWM1CON register (Register 16-2) set the delay period in terms of microcontroller instruction cycles (TCY or 4 TOSC).
These bits are not available on 28-pin devices as the standard CCP module does not support half-bridge operation. When the CCP1 is programmed for any of the enhanced PWM modes, the active output pins may be configured for auto-shutdown. Auto-shutdown immediately places the enhanced PWM output pins into a defined shutdown state when a shutdown event occurs if the heximal of MCU being read.
A shutdown event can be caused by either of the comparator modules, a low level on the Fault input pin (FLT0) or any combination of these three sources. The comparators may be used to monitor a voltage input proportional to a current being monitored in the bridge circuit. If the voltage exceeds a threshold, the comparator switches state and triggers a shutdown.
Alternatively, a low digital signal on FLT0 can also trigger a shutdown. The auto-shutdown feature can be disabled by not selecting any auto-shutdown sources. The auto-shutdown sources to be used are selected using the ECCPAS2:ECCPAS0 bits (bits<6:4> of the ECCP1AS register).
