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LM2673: Behavior on Short circuit

Motoyasu Hattori
Genius 10895 points
Part Number: LM2673

Hi,

If the load is short-circuited (due to mis-wiring or water drops or dust adhering to the load side during operation) and the load impedance during short-circuit assumes about 0.2Ω,

(1) Calculate simply, the short-circuit current is 12V / 0.2Ω = 60A. With the current limit of 4.5A, wouldn't it overshoot to 4.5A or more?  If so, how much will you overshoot?

(2) Even if overshoot occurs, can it be kept within the range where the regulator is NO damage?

(3) How long does it take from the detection of a current of 4.5A or more to the restriction?

(4) When the current limit is working (limited to 4.5A), will the output voltage drop? Will it maintain 12V?

(5) If the short-circuit current shifts from 4.5A or more to about 2A by another protection circuit, will the current limit function be released and return to normal operation?

 

The following condition is as follows:

Device : LM2673T-ADJ
Input : DC20-30V
Output : About 12V (R1=1kΩ、R2=9.1kΩ)
Current Limit : About 4.5A(Radj=8.2kΩ)

Thanks and best regards,
M.HATTORI.

  • 0
    TI__Mastermind 35210 points

    Hattori-san,

    0.2ohm is considered hard short.

    (1) Calculate simply, the short-circuit current is 12V / 0.2Ω = 60A. With the current limit of 4.5A, wouldn't it overshoot to 4.5A or more?  If so, how much will you overshoot?

    HS current limit is programmable and specified in dartasheet. Current limit  is well controlled.Output will fall to ground with hard short

    (2) Even if overshoot occurs, can it be kept within the range where the regulator is NO damage?

    No damage will occur to regulator with appropriate design. Ensure that inductor selection is appropriate for HS current limit slection

    (3) How long does it take from the detection of a current of 4.5A or more to the restriction?

    HS is turned off immediately once peak current limit is exceeded.

    (4) When the current limit is working (limited to 4.5A), will the output voltage drop? Will it maintain 12V?

    It will drop to ground with hard short 

    (5) If the short-circuit current shifts from 4.5A or more to about 2A by another protection circuit, will the current limit function be released and return to normal operation?

    If peak current limit is note exceeded, device will operate in normal fashion. Please see datasheet text for current protection scheme.