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TPS2491: Uncertainties dv/dt control

Jasper Keuning
Prodigy 70 points
Part Number: TPS2491
Other Parts Discussed in Thread: LM5060

Hi, 

I want to limit inrush current to my board which has 2200uF input capacitance and is switched on by a relay. I've selected the TPS2491 for this task. My intention is only to use the enable and gate drive functionality of this IC (I prefer not to include a sense resistor) so I shorted SENSE to VCC and Timer to GND. In order to limit the current I've connected a capacitor (with series resistor) to the GATE output pin. 

This works great, the output voltage ramps up as expected. However when I do a tolerance analysis on the dv/dt I am a little bit confused therefore a few questions I hope someone can answer.

Q: The datasheet claims the gate sourcing current is 15uA - 35uA. Your design calculator spreadsheet mentions 16uA - 28uA. Which value should I believe?

Q: there is a significant temperature dependancy for the gate sourcing current. Is it already incorporated in the numbers above? Or should it be added for worst case calculations?

Q: Is the sourcing current range a TI production tolerance or a life-time tolerance? In other words, can I measure the value during my production phase and compensate for it one time and then only account for temperature influences?

I hope someone can shed some light on these items.

With kind regards,

Jasper Keuning

FYI,

input voltage is up to 40VDC

I want to be able to draw up to 16A from the 40VDC after the system has booted

  • 0
    TI__Genius 10370 points

    Hi Jasper,

    Welcome to e2e! My comments to your questions are below:

    Q: The datasheet claims the gate sourcing current is 15uA - 35uA. Your design calculator spreadsheet mentions 16uA - 28uA. Which value should I believe?

    A: The Datasheet has the correct values (15uA - 35uA). The calculator tool is used for the TPS249x/8x family. But the typical value is what's used on the calculator tool, which is the same for both family of parts (22uA). 

    Q: there is a significant temperature dependency for the gate sourcing current. Is it already incorporated in the numbers above? Or should it be added for worst case calculations?

    A: Typical values are used for the dv/dt portion of our calculator tool. To offset any min and max values, we recommend a SOA margin above 1.5 for a robust design.

    Q: Is the sourcing current range a TI production tolerance or a life-time tolerance? In other words, can I measure the value during my production phase and compensate for it one time and then only account for temperature influences?

    A: The range is at TI production. 

     

    I want to make sure that you know that there is NO short circuit protection without a Rsense value and Ctimer value. If you would like for me to take a look and review your calculator spreadsheet, feel free to attach it. Also, since the application won't be using our current limit, power limit, or short protection, another option (and cheaper) to use might be the LM5060. I hope this helps :-)

     

    Best Regards,

    Aramis P. Alvarez

  • 0 in reply to Aramis P. Alvarez
    Prodigy 70 points

    Hello Aramis,

    Thank you for your quick and clear response. I agree the LM5060 is a better option, but we started out with the TPS2491 and due to the low volume we don't want to 'risk' switching to another component.

    With kind regards,

    Jasper Keuning