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TPS61090 Start Up current

user1557649
Prodigy 60 points
Other Parts Discussed in Thread: TPS61090, TPS2553, TPS61099, TPS2553-1

We want to design and guarantee that the TPS61090 can start up reliably when there is an input current limit. Although it has been known that the system can be started without any problem in the actual machine check, the output waveform does not operate as the data sheet because of the current limitation. In order to explain this operation, could you tell me the principle of operation of this IC at startup?

Thank you for your coopration.

<Background of questions>
The INPUT of the TPS61090 is powered by USB. In order to conform to the USB 2.0 standard, a 500 mA current limit is applied. Since the voltage is lowered by the USB cable, the input power of TPS61090 becomes about 4V. I want to boost this 4V to 5V.
However, since the INPUT current is limited to 500mA, it behaves like the attached waveform. Probably, if there is no limit on the INPUT current, the output voltage starts up smoothly to 5 V, but due to the lack of current and the voltage shortage, it does not start smoothly and the output voltage drops once.
I do not need to be smooth, but I want to guarantee that I can always output 5V, but I can not explain the fact that it starts up absolutely because I do not know the operation principle at the time of startup of TPS61090. Input power> output power, so I think that it will start without problems. Could you tell me the starting principle of this IC?

[Electrical Schematic of Circuit Board]

[Wavefrms]

  • 0
    TI__Mastermind 34201 points
    Hi,

    Can you upload the schematic and waveform one more time?
    When the device enables the internal startup cycle starts with the first step, the precharge phase. During precharge, the rectifying switch is turned on until the output capacitor is charged to a value close to the input voltage. The rectifying switch current is limited in that phase. This also limits the output current under short-circuit conditions at the output. After charging the output capacitor to the input voltage the device starts switching. Until
    the output voltage is reached, the boost switch current limit is set to 40% of its nominal value to avoid high peak currents at the battery during startup. When the output voltage is reached, the regulator takes control and the switch current limit is set back to 100%.
  • 0 in reply to Zack Liu
    Prodigy 60 points

    Hi, Zack Liu san,

    Thank you for your early reply.

    I have tried to upload the "Electrical Schematic of Circuit Board" and "Waveform" again.I appreciate for you to check them and reply again.

    Sincerely,

    Toru

    TPS61090_Start Up at Input current limmit .xlsx

  • 0 in reply to user1557649
    TI__Mastermind 34201 points
    Hi Toru,

    TPS61099 output voltage drops down when it reaches 4.5V, and the green color current curve shows that the circuit triggers TPS2553 current limit.
    TPS61099 switch current limit is set to 40% of its nominal value, 0.88A, to avoid high peak currents at the battery during startup. So TPS61099 is trying to get more input current from USB but TPS2553 limits the input current to 0.5A.
    In TPS2553 datasheet part 9.3.1, The TPS255x devices limits the current to IOS until the overload condition is removed or the device begins to thermal cycle. The TPS255x-1 devices will limit the current to IOS until the overload condition is removed or the internal deglitch time (7.5-ms typical) is reached and the device is turned off. Which device are you using, TPS2553 or TPS2553-1? The device may reach thermal cycle or in ternal deglitch. But anyway, when thermal cycle or deglitch is off, TPS2553 current limit is removed, TPS61099 can get enough energy in the next cycle to get to 5V.
  • 0 in reply to Zack Liu
    TI__Mastermind 34201 points
    Hi Toru,

    I'll close this thread since haven't gotten replies from you. You can post a new thread if you have new findings. Thanks.