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LM61460EVM: Question about external component

Yuta Kurimoto
Expert 8780 points
Part Number: LM61460EVM
Other Parts Discussed in Thread: LM61460-Q1,

Hello Team,

I have some questions about LM61460-Q1 EVM.

Q. Regarding with RBOOT resistor, I think adding RBOOT resistor decrease the FET turn on slew rate, then the noise will become small. On the other hand, Adding snubber circuit will also improve the noise performance. Do you know how effective are the RBOOT resistor and Snubber circuit respectively? OR is there any noise data when adding RBOOT resistor or when adding snubber circuit. Customer doesn't want to add snubber circuit if possible. This is because the snubber capacitor short may cause failure. So Customer want to know how much the RBOOT resistor is effective for increasing noise performance. 

Q. The LM61460EVM using 4.7uH winding inductor for L1. But customer want to use multilayer inductor for downsizing. Problem is that they can't find the multilayer inductor which has 4.7uH, 4A> rated current in the market. So they will plan to choice 1.5uH, 4A> rated current inductor for L1. In that case, is there any problem to affect the output stability or oscillation?

Thanks,

Yuta Kurimoto

  • 0
    TI__Mastermind 27045 points

    Hi Yuta,

    I will send you email for Q1.

    For Q2, there are two suggestion:

    1. check if the Fsw can be 2MHz to use smaller inductor

    2. use two inductor in series.

    Too small inductor will product higher output ripple and may limit output current capability at high Vin.

    B R

    Andy

  • 0 in reply to Andy Chen
    TI__Expert 8780 points

    Hello Andy,

    Thanks for your answer.

    For Q1, I'm looking for your email.

    For Q2, They set the Fsw 2MHz so they don't concern about the output ripple. Customer just concerns output stability(oscillation). Changing the inductance from 4.7uH to 1.5uH affect the output stability(Oscillation)? I'm not familiar with feedback loop calculation, so I'm not sure if the too small inductance may cause some conflict other than output ripple.

    Thanks,

    Yuta Kurimoto

  • 0 in reply to Yuta Kurimoto
    TI__Mastermind 27045 points

    Hi Yuta,

    Data sheet recommended 1.5uH for 5Vout at 2MHz, output capacitor is 2pcs or more 22uF 16V ceramic cap. loop is table with this configuration.

    B R

    Andy

  • 0 in reply to Andy Chen
    TI__Expert 8780 points

    Hello Andy,

    Thanks for your answer.

    I understood about the Question 2. let me close this.

    I will appreciate if you can send information by email to me.

    Regards,

    Yuta Kurimoto