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TPS23734: VDD range definition

Charles Zhang1
Expert 3430 points
Part Number: TPS23734

Tool/software:

Hi Team,

According to IEEE802.3 standard, voltage range on PD side may be down to 37V. If the voltage drop of the bridge diode is also taken into consideration, the actual VDD on PD controller would be lower. 

So I am curious about the reason that TI specifies 37.6V as VDD rising threshold, why not set VDD rising threshold lower to accommodate a wider PD input voltage range?

Thanks.

Regards,

Charles

  • 0
    TI__Mastermind 37101 points

    Hi Charles,

    Thanks for reaching out!

    When PD is turning on, the Ethernet cable has very low current and very low voltage drop on the cable (V_cable = I_cable * R_cable = ~0V). This means V_pse(out) - 2 x V_diode(f) - V_cable = V_pd(in). While minimum PSE output voltage is 44V.

    For the 802.3bt standard. The PD turn on voltage is 30 - 42 V as shown below, which leaves at least 2V for diode voltage drop.

    Best regards,

    Diang