This question is concerning the (lack of) configurability of the dead-band timing for different PWM pin polarities. The application is for a DC/DC converter utilizing a half-bridge of IGBTs. I am using a TMS320F2812 DSP to generate a symmetric PWM using Event Manager A's GP Timer 1, Full Compare Unit, and Dead-Band Timer. For reference, consider page 60 of 152 and Figure 2-5 in application note spru065e. For the purpose of this discussion, consider only outputs PWM1 and PWM2, driven from Dead Band Unit A, driven from Compare Unit 1, driven from the symmetric waveform generator of GP Timer 1.
In my application, PWM1 and PWM2 are a complimentary pair: PWM1 drives a high-side switch in a half bridge and is active high (when pin PWM1 is high, the high-side switch is on). PWM2 drives the low-side switch and is also active high (when pin PWM2 is high, the low-side switch is on). To generate complimentary signals, the ACTRA register is configured such that one of the two pins is active low and the other is active high. There are two such cases. The first problem is that one of these configurations correctly generates a "dead time" and the other configuration actually generates an "overlap conduction / shoot through time," which will damage the converter.
This, in itself, would not be a problem as there is one combination which works. The problem is that this working combination centers the "off time" around the zero crossing of Timer T1's T1CNT. My application requires me to invert the polarity of the PWMs such that the "on time" is centered around T1CNT = 0. I can not find a combination in the T1CON, GPTCONA, COMCONA, DBTCONA, and ACTRA registers which will allow such a scenario. The simple question is: can I change the polarity of the signal PHx, the output of the symmetric waveform generator?
Is there any solution purely within the DSP, without relying on external logic?
Thanks to all in advance.
