5 CMPSS to Save Extra GPIO for Fast Protection

Generally, it is common to use external comparators to achieve protections such as OVP and OCP. These external comparators then communicate their trip information to the device through GPIO pins which are then used to trip the ePWMs. The F28004x device has internal comparators and hence eliminates the need for external comparators and required GPIOs. The CMPSS outputs can be brought out on GPIOs for debug purposes but this is not required for normal operation.

By design, the CMPSS outputs are routed directly to the EPWM through the EPWM X-BAR for tripping purposes. There are 7 Comparator Subsystems (CMPSS) in the F28004x device, with two comparators each for a total of 14 comparators. As shown in Figure 2, the delay from CMPINx input change to ePWM output trip action is approximately within 55 ns, which is comparable to discrete comparators. Furthermore, since the CMPSS inputs are multiplexed with the ADC inputs, in-time protection happens as the ADC samples the input signal. For detailed information on the CMPSS, see the CMPSS chapter in the TMS320F28004x Piccolo Microcontrollers Technical Reference Manual. And, the software examples can be found in C2000Ware folder located at: C:\ti\c2000\C2000Ware_<version_number>\driverlib\f28004x\examples\cmpss.

Figure 2. CMPSS Protection Timing