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TPS23753A: DEN disable

Karthik Puliyadi
Prodigy 160 points
Part Number: TPS23753A

Hi

As per datasheet DEN  required to be 3 to 5V to disable POE Interface, What is the current expect to disable to DEN at VDD=48V when it is pulled up to 24.9K

At 1.8mA Optocoupler input current , i t  enable the opto output to LOW & disable PoE interface. So what is the current expected Ic to disable it

Thanks & Regard

Karthik 

  • 0
    TI__Mastermind 41780 points
    Hi Karthik,

    Are you asking how to rate the pull up resistor based on the current flowing through the pull up when detection goes LOW? I recommend looking at section 3.5 of the below app note. This discusses consideration for this circuit to keep the PSE disconnected when the adapter is inputted. It also shows the power rating for the pull resistor.

    www.ti.com/.../slva306a.pdf
  • 0 in reply to Darwin Fernandez
    Prodigy 160 points
    Hi Darwin

    As per Schematics, "ADAPTER_EN" is driven by the optocoupler.

    When 24VPB(Other source) is not available "ADAPTER_EN" will be pullup (I=48/24.9K=>1.9mA). Rite now when "ADAPTER_EN" is made pulldown through optocoupler What is the current required on collector of optocoupler in order to disable the POE (i.e Vce=0.4).

    As understood based on CTR of optocoupler, output current will be varied on input current at optocoupler. Currently when i measured optocoupler input 24VPB current it was around 1.8mA to generate VCE=4.1v. So PoE is disabled

    At same input when current input is 1.6mA it generate 6.6V and PoE is enable state.

    So how to calculate the collector current to disable PoE