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LMR16010: LMR16010

Charles Nutter99418
Prodigy 80 points
Part Number: LMR16010

We want to use a 2.5V to 5V output from a microcontroller to gate on and off very fast the operation of the LMR16010 regulator chip. Using the enable is too slow because of the 4 ms soft start in the LMR so we want to use the FB pin to turn on or off the LMR but do not know if it is allowed and we do not know how fast it might work.  We are hoping we can gate on or off the LMR at a repetition rate of at least 20KHZ. 

  • 0
    Prodigy 80 points
    We would be using the LMR to operate at 1 megahertz and gating the LMR at arious PWM or on/off from a uC chip.
  • 0 in reply to Charles Nutter99418
    Prodigy 80 points
    We receied no answer from TI as of yet.
  • 0 in reply to Charles Nutter99418
    TI__Mastermind 23825 points

    Hi Charles,

    I believe that this is not recommended because you might have an overshoot at the output, in order to turn the device off using FB you have to disconnect the top feedback resistor and apply a voltage on the FB higher than the internal reference voltage. But this way you will not have any regulation at all. 

    Applying a voltage directly on the FB, then the resistor divider will cause your output to scale up and no regulation can be achieved

    Thanks
    -Arief

  • 0 in reply to Arief Hernadi
    Prodigy 80 points
    Arief, Thank you. The input supply votaage to the LMR chip is 12VDC and I need 5 to 12VDC output. No industor at the LMR is used because I am using the LMR to drive the gate of fast FET. I understand how the FB works but wanted to know how fast I can gate the LmR output on and offusing the FB pin. I am looking for high duty duty-cycle pulses to the fast FET gate. Hopefully, the FB can swith the LMR pulses on and of in a 100NS or so. I can use a resistor divider to set the LMR duty-cycle if needed. It appears to me that the FD must operate the on/off of the LMR very quickly. A Spice model of the LMR might be helpful. Can you run a spice emulation from your side. I need a SOIC8 chip to fit where another SOIC chip will be removed so I am putting the LMR on the SOIC8 pads. In Adddition, my driing source to the FB pin on LMR has a rep rate of max 20 KHZ at 3.3V and I need to switch the inductor on my LED at 1MHZ to 2MHZ ro get the inductor size down and cheap, too.
  • 0 in reply to Charles Nutter99418
    Prodigy 80 points

    Ariel! I have a 10-ohm resistor in series with the gate of FET. When the LMR starts pulsing the LMR will be measuring the FET gate voltage that will be detected by the FB and set to turn off the pulse when the gate is charged and the FET is on. My pulses from the uC are feed through a resistor to the FB divider so the FB never goes dangerously out of FB range.  Concurrently the LMR will detect the current output t the FET is high (1 amp) then drops quickly because the FET gate will be charged so both FB and drop in current suddenly should kill the pulse from the LMR.  The cycle should repeat itself until the uC signal pulls the FD high enough to stop the LMR and create the desired deadtime. The rise time of the uC pulse is 20 ns.  I think the bootstrap cap should be charged each cycle.in this scenario. Does this make any sense to you?

  • 0 in reply to Charles Nutter99418
    TI__Mastermind 23825 points
    Hi,

    Can you use a gate driver to drive the FET? Here is one example
    www.ti.com/.../ucc27528-q1.pdf