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LV5144: How to use this IC

masao hirai
Prodigy 10 points
Part Number: LV5144
Other Parts Discussed in Thread: LM70860, LM5146, LM5145, LM5190

Tool/software:

(1)Can LV5144  be used in a power supply with the following specifications: input voltage 53V～ 58V, output voltage 51V, 5.6A?

(2)This IC does not operate in sync with an external signal. In that case, how should I handle "7p" and "8p"?

(3)Should I leave "15p" open?

(4)Please provide me with some example circuits using this IC.

  • 0
    TI__Guru 73602 points

    Hi Hirai-san,

    1. Yes, the LV5144 is feasible, but why not use a converter with integrated FETs, e.g. LM70860?

    2. It accepts external SYNC signal.

    3. The NC pins can be connected to GND for better heat spreading.

    4. See the apps examples in the data sheet - also refer to the LM5145 and LM5146 files.

    Regards,

    Tim

  • +1
    Prodigy 10 points

    Hi Tim

    Thank you for your quick response.

    There seems to have been a slight misunderstanding.

    When not using external synchronization, that is, when operating with internal oscillation, should "SYNCIN" be pulled down or pulled up with a resistor?

    Is "SYNCOUT" okay to be OPEN?

  • 0 in reply to masao hirai
    TI__Guru 73602 points

    Yes, SYNCOUT should be open if not used.

    And there is an internal 20kΩ resistor pulldown on SYNCIN, so leave it open or tied to GND for diode emulation mode. Connect to VCC for FPWM mode.

  • 0 in reply to Timothy Hegarty
    Prodigy 10 points

    Thank you very much. I understand well. Again,

  • 0 in reply to masao hirai
    TI__Guru 73602 points

    Great, thank you.

  • 0 in reply to Timothy Hegarty
    Prodigy 10 points

    Hi Tim

    Thank you for your advice so far.

    The experiment is proceeding without any problems so far.

    There is one additional thing I would like to check: the capacitor connected to the "SS/TRK" pin.

    I want to set the soft start to about 1 second, so I am connecting a 10uF capacitor.

    How many uF can be connected to this pin?

  • 0 in reply to masao hirai
    TI__Guru 73602 points

    Not sure of there's any limit, but 1 second is the highest I've heard for that. Why so long?

  • 0 in reply to Timothy Hegarty
    Prodigy 10 points

    We are operating it as a constant current power supply. I think it is also related to the value of the output smoothing capacitor, but it is to suppress the overshoot of the output current at startup. In reality, I think it will be about 0.5 seconds.

  • 0 in reply to masao hirai
    TI__Guru 73602 points

    Hi Hirai-san,

    The LM5190 is a better choice if you need to operate with CC (no external circuit required).

    Regards,

    Tim

  • 0 in reply to Timothy Hegarty
    Prodigy 10 points

    Thank you for the suggestion, TIM.

    ■However, I have considered the LM5190, but it cannot be used because the current sensing part is on the high side.

    The product this time will be used to switch a constant current of 200mA to 5.6A in 32 precise steps.

    For this, the current sensing resistor itself is designed to be switched by a FET.

    Also, since the switching circuit must be based on GND,

    ■I have created a separate constant current feedback circuit, which is input to the FB pin of the LM5144.

    By the way, regarding the capacitor value to be connected to the SS pin this time, it seems it will be 4.7uF.

    I suspect that the potential issue might be related to the power of the FET discharging the internal SS pin of the IC.

    If 4.7uF is not acceptable, a simple measure would be to connect a resistor in series with the 4.7uF (+ directly add 0.022uF), but I am thinking of establishing a separate soft-start circuit externally.

    ■Please let me know whether 4.7uF is acceptable or not.

  • 0 in reply to masao hirai
    TI__Guru 73602 points

    4.7uF may be okay, but it may take a while for the internal pulldown FET to discharge SS to zero.

    Note that the LM5190 has an ISET input specifically for varying the CC setpoint...you would not manipulate the shunt (current sense resistor), as that sets up the loop for current-mode control.

  • 0 in reply to Timothy Hegarty
    Prodigy 10 points

    Thank you for your response.

    When using the LM5190, I opted not to use a fixed current detection resistor because it inevitably lowers the constant current accuracy when the current is low.

    To improve current accuracy, I ensure precision by fixing the reference voltage and varying the current detection resistor.

    I will confirm sufficiently regarding the discharge time of 4.7uF.

  • 0 in reply to masao hirai
    TI__Guru 73602 points

    okay, sounds a bit risky adjusting the shunt, as it will change the loop gain.