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LMR16006 Current limit

K.Hamamoto
Guru 12155 points
Other Parts Discussed in Thread: LMR16006

Hi

Our customer is evaluating LMR16006. Because this device is small and easy to use.

They would like to know about current limit operation and limit value.

1. How does this device control the current limit? Can we set the current limit value by external component?

    We understand the current is compared with internal COMP voltage at each cycle.

    The current limit protection works (= turn off the high side FET) if the peak current voltage is crossed the COMP voltage.

2. Could you provide the minimum of current limit (= Peak current limit : Ilimit)?

3. What does Peak current limit mean?

    This current means the current of high side switch. This mean that this peak current is depends on VIn and Inductor.

    On the datasheet  there is the Peak current limit. Is there any condition? (Vin and Inductor)

Regards,

Koji Hamamoto

   

  • 0
    TI__Genius 10115 points

    The Current limit is tested at 12V. It is an open loop test of the comparator current trip point that is correlated to the bench.

    Slight changes in the current limit can be made by adjusting the inductor value to adjust the peak to peak ripple current.  

    You can lower the current limit with a current sense  resistor and an operational amplifier that allows high common mode voltages, that is configured to pull down on the FB voltage once a threshold is reached.  However if the customers goal is small and easy to use this adds significant complexity.

    I will see if I can find data on the minimum current limit.

    Marc

     

  • 0 in reply to Marc Davis-Marsh
    Guru 12155 points

    Hi Marc-san

    Thank you for your support.

    I understand the current limit is at open loop test and Vin=12.However there is not inductor condition. How much is that?

    Also could you  provide us the minimum value of the limit at your condition?

    Regards,

    Koji Hamamoto

  • 0 in reply to K.Hamamoto
    TI__Genius 10115 points

    Hi Koji-san

    The lower limit is 1.15 

    I will check again on the inductor value it is tested with.

    Marc

  • 0 in reply to Marc Davis-Marsh
    Guru 12155 points

    Hi Marc-san

    Thank you very much for your support.

    Could you check again please about test condition of Ilimit on the datasheet.

    Because our customer are confused about that. (Of cause they understand that peak current is depends on inductor and ripple.)

     

    Regards,

    Koji Hamamoto

  • Anonymous
    0 Anonymous
    Hi Hamamoto,
    1. The peak current limit of 1200mA is the maximum peak current ( through the internal switch or inductor) the device can go upto. It is there basically to protect the internal switch. Obviously the inductor selected should have a Saturation current value less than 1200mA. The cycle by cycle peak current will be dependent on Vin, vout and L value. Inside the chip, this value is controlled by the corresponding COMP voltage.
    2. The lower limit of current is 90mA ( corresponding COMP ~0.55V) at which point the chip enters Sleep mode.
  • 0 in reply to Anonymous
    Prodigy 10 points
    Hi,

    Apologies for resurrecting this - just a follow up question. What does the LMR16006 do during sleep mode at 90mA? Does it shut off the output? My confusion comes from the data sheet where there is a typical application with a 30mA minimum output current. Does 16006 still work down to 30mA? Lower?

    Second question - I only have 24VAC half wave bridge available to me, so 32-39 volts DC down to regulated 5VDC. What amount of ripple is allowable on the this input? Trying to calculate capacitor sizes.

    Thanks,

    Joe
    (Not a SMPS expert as this question probably shows)
  • 0 in reply to Joe Menard
    TI__Mastermind 34785 points

    Hi Joe,

    LMR16006 works in Eco-mode if load current below 90mA, it's similar as PFM mode which reduce switching frequency to improve light load efficiency, it keeps working in Eco-mode even load is 0mA.

    LMR16006 can works in low drop-out mode when input is close to Vout, but for better output regulation, we suggest lowest Vin=7V for 5V output.

    B R

    Andy Chen