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LM5116: Current Sensing without Diode Emulation

Mike Lee88
Prodigy 80 points
Part Number: LM5116

Hi
Datasheet page.17 (figure 30 RDS(ON) Current Sensing without Diode 
Emulation) . Is that mean, if no sense resistor(Rs) can not achieve DEM?

  • 0
    TI__Guru 74002 points
    Hi Mike,

    Tie DEMB to CSG to enable diode emulation mode. This is achieved by sensing the SW node voltage when a curernt sense resistor is not used.

    Regards,
    Tim
  • 0 in reply to Timothy Hegarty
    TI__Prodigy 690 points

    Hi Tim,

    1. Customer is coufused why the fig.30 title shown "Rdson current sensing without diode emulation". The diode emulation should happen when inductor current become negative, and decided by monitor the voltage between SW and DEMB. No matter we use Rdson sense or put another Rs sense. For fig.30 circuit, it show Rdson sensing connection, but it doesn't mean it's without diode emulation, rgiht?  

    2. And you said "Tie DEMB to CSG to enable diode emulation mode", how to connect to disable diode emulation mode? Add RDEMB=10k will make DEMB pin=0.45v, how to decide RDEMB value and any formula?

    Thanks.

    Regards,

    Lynn

  • 0 in reply to user4979999
    TI__Guru 74002 points
    Hi Lynn,

    Question 1: Diode emulation is configured with the resistor on DEMB (for example 10k) - this is what Figure 30 indicates. This resistor would be zero Ohms to enable diode emulation mode operation (noth Rdson sensing and sense resistor sensing).

    Question 2: Use a large enough resistor at DEMB such that it is greater than the highest SW voltage during low-side FET conduction. This depends on the Rdson of the FET (highest at hot), the max output current, and the minimum spec for the DEMB current with SS high (28uA per the EC table in the data sheet).


    Regards,
    Tim
  • 0 in reply to user4979999
    TI__Guru 74002 points

    Hi Lynn,

    Please click on Resolved if there are no further questions so we can close out this thread.

    Regards,
    Tim