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LM1084-5.0 resets

pf fl
Prodigy 40 points
Other Parts Discussed in Thread: LM1084

Hello,

i have a 12v/9000mAh battery witch powers an ODROID board that consumes from 0.5A to 4A

i used an LM1084-IT 5.0 to convert the 12v to 5v, it works fine, but as the board consumes more and more, the LM1084 stops working

i checked with my multimeter, the load, it seems the IC stops working before reaching 2A, the board does not even start

without the multimeter, the board starts but as i benchmark prime numbers calculations (CPU is a quad core)

the lm1084 stops after like 30 seconds

i used heatsinks that go less than 2C°/W

i wondered if anyone could give me any advice

[edit: the circuits i use is the simplest possible, the + of the battery is linked to the Vin, gnd is linked to the - of the battery. and the Vout is linked to the ODROID board (as the GND of the lm1084]

  • 0
    TI__Expert 3920 points

    Hi,

    As a starting point, can you ensure that the LM1084 is operating within its temp range when the issue occurs? It is possible that thermal shutdown may be causing this due to high operating temp.

    Tim

  • 0 in reply to Tim Reyes
    Prodigy 40 points

    Hi Tim,

    I live in belgium, we barely reach 20°C in the day :-)

    from my calculations, VIn = 12v, the board draws max 4A, so it dissipates around 28W

    i dont know if i use the most appropriate Ic, all this heat is a lot of waste

    also i did not add any caps around the 1084, some people told me it could make it oscillate

    (I dont know if the Tantalum caps are mandatory)

    to sumarize

    my system needs 12V for the motors

    7-12V for an arduino

    5V 5A for the ODROID board

    and 5V supply for the other IC's in the overall system circuit (sensors/MUX/latches...)

    any suggestion ?

  • 0 in reply to Tim Reyes
    Prodigy 40 points

    here are the calculations i made from the datasheet (hope the copy paste from exel wil work)

    Ta 25 °C
    Vin 12 V
    Vout 5 V
    Iin 4 A
    Iload 4 A
    Ig 0 A
    Pd 28 W
    Tj(MAX,CTL) 125 °C
    Tj(MAX,OUT) 150 °C
    ƟCH(compound) 0,2 °C/W
    ƟJC(CTL) 0,65 °C/W
    ƟJC(OUT) 2,7 °C/W
    ƟJA(CTL) 3,5714285714 °C/W
    ƟJA(OUT) 3500 °C/W
    ƟHA(MAX,CTL) 2,7214285714 °C/W
    ƟHA(MAX,OUT) 3497,1 °C/W

    I would need 2.72 °C/W and the black heatsink is less than 2C°/W

    I am wondering if the lm1084 is not corrupt somehow or maybe becos of the missing caps

    I'll see if i can find Tantalum caps

  • 0 in reply to pf fl
    Prodigy 40 points

    ok so i added a 10uF Elec. and a 10uF Tantalum and it seems so far the problem is gone :-)