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TPS40077 / series resistor of SW pin

K.Yaita
Guru 29690 points
Other Parts Discussed in Thread: TPS40077
Hi Team,
 
I'd like to ask about TPS40077.
In datasheet P.12, there is following description about series resistor of SW pin. 
 
If this series resistor is more than 1.5Ω, is there any concern?
 
Best regards,
Yaita
  • 0
    Guru 29690 points
    Could you please give me your advice?
     
    Best Regards,
    Yaita
  • 0 in reply to K.Yaita
    Guru 29690 points
    My customer concerns if  it have any affect at OCP when this resistor(1.5Ω) become big.
    Your support would be appreciated.
     
    Best Regards,
    Yaita
  • 0
    TI__Mastermind 48200 points

    Yaita,

    My name is Peter James Miller.  I am one of the support engineers for TI.

     

    A resistor placed in series with the SW pin has several system level effects beyond the protection described in the datasheet.  In addition to protecting the pin from substrate current induced when a negaive voltage is applied to the pin during the body diode conduction time and ringing when the high-side FET is turned off - especially during an over current fault response, this resistor slows down the high-side MOSFET gate transition (switching) time and alters the TPS40077's sensing of the switch node for dead-time control.

    A 1.5 Ohm to 3.3 Ohm resistor is generationally considered safe and will offer minimal impact on the system efficiency.  Resitors values larger than 3.3 Ohms are not recommended as they can introduce sensing errors with the Predictive Gate Delay dead-time control circuit and negatively impact operation.