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TPS630250 start-up

Martin Dusek
Intellectual 340 points
Other Parts Discussed in Thread: TPS630250, TPS63050

Hello,

are these valid conditions for TPS630250 buck boost converter? Will it start-up correctly?

VIN and VINA is 4 V, externally 100 mA limited. There is 10 mF capacitor connected directly to TPS630250's output. During start-up, VIN and VINA voltage will surely drop (100 mA limitation) due to capacitor charging.

  • 0
    TI__Expert 5425 points

    The TPS630250 is rated for more than 3.5A on the input. 100mA is significantly lower than that. The current limit of the external source will force the supply voltage to drop below the UVLO of the TPS630250 at every attempt to start, since TPS63025 will try to pull higher current from the external source. In UVLO condition TPS630250 will not anymore pull current from the external source and its voltage will recover. As soon as it has recovered above the UVLO threshold the TPS630250 will attempt to start again. I think it will depend on the load during startup whether during those startup attempts enough energy is put into the output capacitor to increase the charge more than it discharges during UVLO.

    Why do you plan to use such a high current rated device at such a source? We may have more suitable devices to operate at such conditions.

  • 0 in reply to Juergen
    Intellectual 340 points

    Hi Juergen,

    thanks for your answer. I will describe my situation:

    We are designing USB and battery powered device. Our power supply path is:

    USB and li-ion battery connected to power path management IC with current limiter -> buck boost converter to generate 3.6 V -> big capacitor (buffer for current peaks caused by GSM module)

    Initially, the current limiter is set to 100 mA current limit to comply with USB standard (after USB enumeration the limit will be increased to 1 A). The current consumption of our device during start up is 30 mA.

    If TPS630250 has problems with input current limiter we will have to design some current limiter to limit charging current of capacitor.

    Or is there a better solution?

  • 0 in reply to Martin Dusek
    TI__Expert 5425 points

    Since you anyway need to buffer the energy required for the GSM pulses I would recommend to use a lower current rated buck boost converter, like TPS63050. The average output power may be enough for powering the GSM module, depending on how many GSM bursts you use as a maximum in one cycle.

    In addition TPS63050 would support using an external softstart capacitor and programming lower current limit depending on power availability.