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WEBENCH® Tools: LP2989 input range error

user5064388
Prodigy 10 points
Other Parts Discussed in Thread: LP2989

Tool/software: WEBENCH® Design Tools

Hi Dear,

We need 12V input 5V 500 ma output.So we select LP2989 but we have some problem about input range and output current.                                                                                                                                                            

You look our schematic below picture.

In LP2989 datasheet says  2.1V - 16V  input range but if Vin=6V or 6.75V we get 500 ma current.But if te Vin voltage over 7.5V LP2989 too hot and switch to thermal protection state.

Also we cannot create a schematic for Vin=12V and output current=500ma,but in datasheet  dont say any restriction about Vin and output current.

If you see any mistake about our design please say me and please help us?

  • 0
    TI__Intellectual 2320 points
    Dear user,

    We will get back to you once we found out the reason for design not being created for 12Vin -> 5Vout.

    Thanks & Regards,
    Harish
  • 0 in reply to Harish K R
    Genius 4910 points
    Dear User,

    For Vinmin=12V,VinMax=12,Vout=5V, Iout=0.4A and Ta =30C, the drop across the LDO is high causing power dissipation to be high and causing the junction temperature to exceed above the rated Tj for the device.

    That’s why WEBENCH is not able to create a design for this condition.

    For Vin of 12V, Vout of 5V, you can theoretically go up to 0.08A

    Here is a WEBENCH design at Iout of 0.08A. You might be able to go slightly higher Iout with a better layout, but it depends on the thermal performance of your specific layout which is hard to estimate theoretically.

    webench.ti.com/.../SD2.cgi

    Thanks and Regards,
    Atul