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TPS54560B: device output behavior upon vehicle cold start/ vehicle battery drain condition

Leo Chow
Expert 3120 points
Part Number: TPS54560B
Other Parts Discussed in Thread: TPS54560EVM-515

Hi,

In my use case I'm having TPS54560B configured to provide 12V output and the input is from the vehicle battery (13.8V typical provided engine is running).

I'm curious to know if there are conditions in such the battery drains and the voltage falls lower than 13.8V and gradually reduces lower than 12V, will the output follow the input with some drop within the device. Assuming i'm referring to Vout calculation as per datasheet, will I be expecting fluctuating voltage?

Can I use webench to simulate case whereby the battery voltage is 12V or lower to observe to output voltage behavior? 

Regards,

Leo

  • 0
    TI__Expert 3835 points

    Hi Leo,

    You cannot simulate on Webench when the input voltage is the same as the ideal output voltage.

    You can calculate the minimum input voltage using equation 1 on section 7.3.4 of the datasheet. This will calculate the minimum input voltage required to regulate the output voltage. Section 8.2.2.10 provides an example. In this mode, the converter will operate in dropout with D = 100%. When the boot cap voltage falls below the boot UVLO threshold of 2.1V, a boot refresh occurs and recharges the boot cap.

    When the input voltage falls below the minimum input voltage the output voltage can vary depending on loop stability and external components. I can verify on an EVM given the parameters and specs.

    Thanks,

    Ethan  

  • 0 in reply to Ethan T
    TI__Expert 3120 points

    Hi Ethan,

    In my use case it's targeted for car audio. The situation i might face is when is engine is off and the accessories connected to the vehicle battery are on & i'm powering on an audio amp using this device. Assuming if my audio amp is driving loud volume 10W @ 4ohm audio, the buck is rated at 5A. 

    Audio AMP in the mobile radio may be playing at loud volume 10W @ 4ohm audio.. so the Buck converter load to be rated at 5A.

    Here's some specs i'm using for my case.

    Input  to the radio: 10.8V (Minimum) and 28.8 (maximum)

    Vout (buck) : 12V

    Iout (buck) : 5A rated. A switching load of 3 to 4 Amp may be used for the test.

  • 0 in reply to Leo Chow
    TI__Expert 3835 points

    Hi Leo,

    My set-up uses the  TPS54560EVM-515 and changing the FB resistors to have a 12V output at 4A load in room temperature.

    I saw max duty cycle operation at around 13V. After that, the output voltage does track the input down to 10.8V with about a  1V drop. When passing dropout operation, the SW node does modulate and fold backs by lowering the frequency to keep the high-side FET as long as possible. The frequency does get in the audible frequency range because I start hearing it. 

    Thanks,

    Ethan