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TLV62130: using FSW pin

TommyDam
Prodigy 220 points
Part Number: TLV62130

Good morning.

I'm using two TLV62130 on my board to generate two different voltages. I want use the two TLV62130 with two different switching frequency. Reading datasheet, I have a doubt about FSW pin. Datasheet reports: "It is mandatory to start with FSW=Low to limit inrush current, which can be done by connecting to VOUT or PG".  I have three questions:

1. What does "FSW=low" mean? Low level or low frequency (1.25 MHz) ?

2. At startup, must I use FSW = 1.25 MHz or FSW = 2.5 MHz?

3. Can I change switching frequency without ripple in the output during powering load?

Thanks in advance.

Best regards,

Tommaso

  • 0
    TI__Expert 3465 points
    Hello Tommaso,

    thanks for inquiring us. Coming to your question:

    1. FSW=Low means that the FSW logic level must be low (below 0.3V according to section 7.5 of the datasheet) hence the converter will run at 2.5MHz, it's higher sw freq.

    2.At startup you must use 2.5MHz, that's why FSW=Low. If you want to keep this sw freq for the whole operation, you can pull FSW to ground (or let it floating). If instead you want to operate at 1.25 MHz, after the startup you must hook FSW at an High level (above 0.9V according to section 7.5 of the datasheet) which happens automatically when FSW is connected to VOUT or PG.

    3.What do you mean by "without ripple" ? You can anyway change FSW during normal operation, but because of the nature of a buck converter lower sw freq means higher ripple.
  • 0 in reply to Emmanuel Granatello
    Prodigy 220 points

    Hello.

    About the different questions:

    1. Ok. Is there an error in the datasheet?  "It is mandatory to start with FSW=Low to limit inrush current, which can be done by connecting to VOUT or PG".

    2. Ok.

    3. I used a bad expression. If I change switching frequency during operation, does the output have variations, oscillation, drop,etc..?

    Thanks for the reply.

    Tommaso

  • 0 in reply to TommyDam
    TI__Expert 3465 points

    Hello Tommaso,

    on your answers:

    1. There is no error on the datasheet. When the device starts-up Vout, or better say Vfb, is below the target, hence PG is in low impedance (that means logic low if pulled up by a resistor to Vout) until Vout reaches 95% (typical) of the target voltage. Connecting directly to Vout will serve the same purpose, given you setup a proper resistor divider to meet the FSW logic threshold at the desired Vout voltage.

    Note: When one wants to use the PG technique, I would recommend to get the TLV62130A, since the PG is kept in low impedance also before the start-up procedure commence.   

    3.When changing the sw freq during operation, one will observe a slight transient response on Vout, but thanks to the DCS control, the transition is seamless.