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TPS4811-Q1: BST Behavior Clarification

Matt Calvo
Genius 14745 points
Part Number: TPS4811-Q1

Tool/software:

Hey Power Switches Team,

I have a customer evaluating the TPS4811-Q1 for a project and we were hoping your team could help clarify the BST behavior for a potential use-case. Please see a summary of our inquiry below!

We're investigating some potential uses of the TPS4811-Q1, and would like some clarification on the role V(BST_UVLOR) plays in the component. If the driver is enabled, with PU pulled up to BST, and then there is a disruption in the system that pulls PU and BST below V(BST_UVLOR) relative to SRC, what is the behavior of the part? Would it enable PD to turn off the output? Does it assert either of the fault pins? I only see V(BST_UVLOR) mentioned with regard to turn on behaviors in the datasheet, so it isn't clear if it remains active after the initial transition.

-Matt Calvo

  • 0
    TI__Expert 8250 points

    Hi Matt, 

    V_BST-UVLOR is used for the start up of the device. The charge pump will activate once Vs and EN are high, but the gate drivers wont be active for PU until UVLOR is surpassed. (Even if INP is held HIGH at start with Vs and EN the UVLOR must be reached to turn on gates). 

    In the event of an interruption from UVLO at the input, short circuit, or over current, the PD is always active. There are several logic components monitoring these events and will activate gate logic to pull PD to SRC shutting down the gate of the FET, regardless of what charge the BST has. 

    The FLT pin will assert for overcurrent and short circuit events. The charge pump will turn off if the voltage drops below BST_UVLOF, which will occur at the time of one of these events. If you are in latch off mode the you will need to toggle , Vs, EN, or INP to restart the BST charging. If in auto retry then this will occur periodically while waiting for the FLT to be removed. 

    Thank you,

    Sarah

  • 0 in reply to Sarah Raines
    TI__Genius 14745 points

    Thank you so much for the detailed reply Sarah!

    I'll go ahead and pass this along to my customer and will have them comment back on this thread directly with any follow-up questions they may have.

    -Matt

  • 0 in reply to Matt Calvo
    TI__Expert 8250 points

    Ok. Thank you. 

    -Sarah