Other Parts Discussed in Thread: BOOSTXL-BUCKCONV
hi,
I was working on the BOOSCTXL-BUCK converter. I ran the f280049 example available in C2000_SDK.
I observe that the switch duty ratio is limited to 0.45. Is there any specific reason for it?
I understand owing to losses, the practical duty ratio is limited, however we can at least go till 0.75.
I also tried Simulink example with maximum duty ratio of 0.6. However, I observe that the inductor current is reduced when output voltage is more than 4.5V.
to summarise following are my concerns:
1) why the duty ratio is limited to 045 in the ti shipped example in TIDM-DC_DC_BUCK?
2) When i try to go beyond 4.5 output voltage, the inductor current has a decreasing trend. At 5V output voltage, the inductor current is reduced to very small value.
However, the input supply current has increased.
I investigated the following things:
- Converter is not going in DCM mode.
Following is my calculation:
Active load on
Rload = 7.5||2 = 1.586Ohm
Average current at 5v = 5/1.586 = 3.1526A
Input voltage = 9V
Switching frequency = 200kHz
Ts = 5us
peak to peak current ripple(dI) = (Input voltage - output voltage)*dutyratio*Ts/L = (9 - 5)*5*5/(9*4.8) = 2.3148A
Imin = 3.1526 -2.3148/2 = 1.9952A
Since Imin is more than 0, the converter should operate in CCM.
- The inductor used has saturation current of 13A. hence I think inductor is not getting saturated.
So I wanted to know whether the converter could be used to get the output voltage of 6V.
