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Original question:

LM5050-1: Gate oscillation problem with a PWM load

LM5050-1: gate voltage abnormal

Hollis Liu
Intellectual 2535 points
Part Number: LM5050-1
Other Parts Discussed in Thread: LM5176

HI team,

I meet similar issue with below item. https://e2e.ti.com/support/power-management/f/196/t/825945?tisearch=e2e-sitesearch&keymatch=LM5050

CH1 is Iin, CH2 is VIN, CH3 is Vout, CH4 is Vgate. 

As our analysis, it should be caused by upstream DCDC converter ripple. So we add the a CAP between VIN and VOUT pin as a filter. We tried 100pf, but failed. After we increase the CAP to 22nF, it works. 

Is there any potential risk to add 22nF CAP between VIN and VOUT? Thanks. 

  • 0
    TI__Intellectual 2535 points

    The issued part is U4. It's upstream DCDC is LM5176. 

    U6 works well and it's input is 6s battery. 

  • 0 in reply to Hollis Liu
    TI__Genius 16305 points

    Hi

    22nF is lot of capacitance and this means the DC/DC converter ripple amplitude is large.

    There are no major risks with this approach, but any transient on VIN could couple through 22nF. VCC_BUS can not have large transients, due to huge capacitance on the bus. So any transient on VIN would couple through 22nF and absorbed by bulk Capacitance on VCC_BUS.

    Other approach is to increase the capacitance on VIN and reduce the capacitance across VIN-VOUT.

    Regards,

    Kari.