• State Resolved
  • Locked Locked
  • Replies 5 replies
  • Subscribers 63 subscribers
  • Views 657 views
  • Users 0 members are here
Support feedback
Options
Options
Similar topics

This thread has been locked.

If you have a related question, please click the "Ask a related question" button in the top right corner. The newly created question will be automatically linked to this question.

LMR62014 not regulating

Glen George
Prodigy 20 points
Other Parts Discussed in Thread: LMR62014

I am using an LMR62014 to generate 20V at 100 mA.  The output briefly goes to 25V and then thermal shutdown quickly kicks in.  If I lower the load resistance the output goes to 30V and then I again get thermal shutdown.  The voltage on the feedback pin is around 1.2V, but there is a lot of noise on it.  The load is purely resistive.  I am using the schematic from the datasheet and a layout very close to that as well.  The inductor is 10 uH, the feedback resistors are 200K and 13.3K, and the feedback capacitor is 130 pF.  Any thoughts on what I might be doing wrong.

  • 0
    TI__Genius 16025 points
    Hi Glen,

    I've received your query and will get back to you shortly.

    Thanks,
    Anston
  • 0 in reply to Anston Lobo
    TI__Expert 3840 points
    Hi Glen - Please also share with us your input voltage supply and a screenshot of your schematic and PCB layout for review.

    Thank you!
    JP
  • 0 in reply to Juan Paulo Fung
    Prodigy 20 points

    Hi,

    The input is a 5V 3A lab benchtop supply.  Attached are the schematic and board layout.

    up.pdf

    stepup.pdf

    Glen

  • 0 in reply to Glen George
    TI__Genius 16025 points
    Hi Glen,

    Are JP 1, JP 2 and JP 3 populated? It is critical that they are all directly connected and not through a jumper. The jumpers add inductance and resistance that can not only throw off stability of the IC but cause large parasitics that diminish the capacitor's effectiveness.

    Remove RL1 through RL4 and check to see if the circuit works.

    Finally if none of these suggestions work, change R2 to 117K and see if it works.

    Thanks,
    Anston
  • 0 in reply to Glen George
    TI__Genius 11085 points
    Glen,
    I think the problem comes from the three jumpers from Cout to Vout. The LMR62014 is a boost converter. The output port of a boost converter has discountinuous current, meaning current going through the diode to the Cout are pulses. In the path of pulsing current, it is critical to properly bypass the high frequency noise coming from high di/dt current slew by capacitors. In this circuit, they are the Couts: C3, C4, and C5.
    When you have jumpers from diode to the Couts, the additional inductances of the jumpers largely degraded the bypassing effect, generating a lot of noise in your circuit. The noise could affect the feedback loop, resulting in unstable Vout.
    Please try to short the two pins of each jumper on the PCB using a piece of solder wick, or copper stripe, or a lot of solder. Then try to run your board again. Hopefully it will reduce the noise level.
    regards, Yang