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Original question:

LV2862: with PoE issue

LV2862: with PoE

Cheng Andy
Prodigy 130 points
Part Number: LV2862

Hi Sir,

Continuation of LV2862 related issues.

e2e.ti.com/.../3600403

I tested the LV2862x chip, when L1=27uH, Cout=10uF, the network connection would be unstable.

When I changed it to L1=47uH, Cout=10uF Qty=3, the network connection was stable.

Can I change L1/Cout like this? Will this change cause problems?

Andy

  • 0
    TI__Expert 5321 points

    Hi Andy,

      LV2862 supply power for PSE or PD?  Since the current is very small, I guess it was a Aux power for PSE chip. If so, you need to check the output voltage ripple.Based on my experience，when voltage ripple>30mV, PoE handshake-detection will be affected. Then it can‘t supply power normally. You should control it <20mV.

      47uH/10uF*3 seems ok. You can test loop stability to check the bode plot.

    BR,

    Victor

     

  • 0 in reply to Victor Yu
    Prodigy 130 points

    Hello Victor,

      Thank you, LV8262 is connected behind the PD chip.

    Can LV2862X PIN4 (chip enable pin) be directly connected to the Vin=57V voltage without connecting the pull-up resistor.

    Andy

  • 0 in reply to Cheng Andy
    TI__Expert 5321 points

    Hi Andy,

      If you don't need a disable function(like UVLO),  SHDN (pin4)  can to be tied to VIN=57V  via a 100-kΩ resistor. This resistance can protect PIN4 from a surge. The absolute maximum voltage of PIN SHUT is 65V, which is close to 57V. So if it is connected  without a resistance, you may face potential risk of overvoltage.

    BR,

    Victor