CCS/SM72295: DC-DC the boost configuration does not work

Hi Marcos,

Thank you for your interest in the SM72295. Im an apps engineer working with this device and will help to answer your questions.

So If understand, when you are in a buck configuration there are output pulses but when you are in the boost configuration there is no output. Assuming your PGOOD, OVP, and used or unused Current sense pins are accounted for I would first like to confirm your configuration. Are you using all 4 switches in a buck-boost configuration? Can you send a schematic of your design, to confirm the switch configuration?

The typical configuration I see for a buck-boost in boost mode is the inductor between the ‘always ON’ high side FET’s source and main FET’s low side drain. In the boost configuration the high side device will be on in a DC state in which the inductor is always connected to VIN. The concern I would see, if you need the high side to be on as a DC switch, is maintaining the high side bias. In this case, even though PGOOD is high, it could it be possible that this high side’s UVLO is preventing the part from switching. Can you confirm the HBB-HSB voltage is below HB-HS falling threshold of 6.2V?

You can see the detailed operation of the two switch boost converter here: www.ti.com/.../slyt584.pdf.
In order to maintain the high side bias there needs to be an isolated bias supply for the high side in the form of a transformer iso supply or a charge pump. You can also read about this here: e2e.ti.com/.../620922

Thanks,