Combining TPS40211 and BQ24617?

Hi Nenad,

I don't expect any problem with this scenario as long as the input source can supply the needed current to boost the output up to 12 V @ 2 A. Running the boost at this low of duty cycle with VIN = 12 V and VOUT = 12 V may cause pulse skipping due to the minimum on time which can contribute to some additional output ripple. You may want to check out an integrated FET option like the TPS55330 for a simpler solution.

Anthony

Hi Anthony,

I have several questions regarding TPS55330 you have recommended. What it its maximum output power, I need to know what output current can be on 12V output? In datasheet it is described  design procedure of boost converter and said that for SEPIC converter a different design approach is required. Where can I find that design approach?

This converter would be 99% of its working hours in mode 12V input -> 12V output, only when for some reason adapter is disconnected converter should boost battery voltage to 12V, so I really want to avoid pulse skipping.

This converter is very important in my design because it will supply a some kind of computer who will restart every time if the voltage goes over 12V +/- 10% limits.

Thanks for your help.

Kind regards,

Nenad Simic

I would recommend the boost design in order to get the most output power. The SEPIC would have the maximum current approximately cut in half but you can find an example of the design procedure in the TPS55340 datasheet.

With the minimum input voltage of 6V, the maximum output power including part to part variations in current limit would be very close to 12 V at 2 A. Assuming 90% efficiency and 30% current ripple in the inductor I calculate a peak current to be 5.23 A. The guaranteed minimum current limit is 5.25A. If you need a little more margin on maximum load it would be better to stick with the controller option.

The TPS55330 would pulse skip but would have less ripple in comparison to the TPS40210. This is because it has a much lower minimum on time. A typical design will very likely not pulse skip due to the DC drop in the schottky diode.

Dear Anthony,

for now I'm closest to decision of using TPS55340 as boost converter, because I do not have much time to try different designs right now, so I believe if it can work with 24V, 1.9A output it can work with 12V 2A output.

Believe it is better to go safe then sorry.

 I have just one more question.

Because we want to try and see how this converter works using evaluation module (TPS55340EVM-017 in this case), can you tell me if I remove resistor  R1 and replace it with 87.6k (to have 12V output) is it still going to work OK and provide 1.9A current on output? For input voltage I would use from 5.5V to 11.8V?

Thanks again for your help.

Best regards,

Nenad

Hi Nenad,

It will likely work fine for up front testing.

However if you want to optimize the design I recommend adjusting the output capacitors and maybe the compensation. With only 12 V output lower voltage rated higher capacitance capacitors could be used. You can make this selection with the aid of WEBENCH or the excel sheet in the product folder.

Best Regards,
Anthony