TPS23753A: Gate Resistor effect IEEE STD 802.3at-2009 inrush current test failed issue

Sam Shyu36

Part Number: TPS23753A

Dear Sir,

We just modify R13 (Gate Resistor ) from 10ohm to 49.9ohm. But the inrush current max. from 335.7mA increase to 421.4mA. Could you help to explanation that why Gate Resistor effect input inrush current? Thanks!

R13 = 10ohm

R13 = 49.9ohm

Best Regards,

Sam

over 6 years ago

0 Darwin Fernandez over 6 years ago

TI__Mastermind 41790 points

Hi Sam,

Increasing the gate resistor will dissipate more overall power in the converter. This means the DCDC efficiency will be less. You may need to decrease your max output current spec.

0 Sam Shyu36 over 6 years ago in reply to Darwin Fernandez

Intellectual 735 points

Hi Darwin,

Increasing the gate resistor the turn on time should be slower. Power on Inrush current should be smaller.
Overall power increasing should be after power on. Is my understanding correct?

Best Regards,

Sam

0 Darwin Fernandez over 6 years ago in reply to Sam Shyu36

TI__Mastermind 41790 points

Hi Sam,

Turn on time will not be that different. Increasing the gate resistor really increases the slew rate of the FET turn ON (more power dissipation).
I suspect the DCDC is switching (ramping up) while the PSE is inrush.

Do you have a load connected to output when you are testing? Can you try reducing the load current?

0 Sam Shyu36 over 6 years ago in reply to Darwin Fernandez

Intellectual 735 points

Hi Darwin,

When doing the POE compatibility test, the system load will not be disconnected for testing. Please refer below test result. Have other suggest for reduce inrush current? Thanks~

System load unbroken the Inrush current 343mA to 424 mA.
Remove the system load for test comparison, the inrush current between 129mA to 387mA, the range is larger.

Best Regards,

Sam

0 Darwin Fernandez over 6 years ago in reply to Sam Shyu36

TI__Mastermind 41790 points

Hi Sam,

You can try increasing C22 to ~40uF to see if this helps.This will delay switching/output power within the the inrush time of the PSE. Thanks!

0 Sam Shyu36 over 6 years ago in reply to Darwin Fernandez

Intellectual 735 points

Hi Darwin,

Thanks for your help~

Best Regards,

Sam

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TPS23753A: Gate Resistor effect IEEE STD 802.3at-2009 inrush current test failed issue