OPA541 and OPA549

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millwood

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Matttcattt said:



but in my case, i just wanted te max limit (0.01 ohms) this seems pointless to me.
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I assume you wanted to be able to reach the 10A peak current output limit. The datasheet isn't clear as to if there is any protection if you short the current sensing resistor. My guess is no, as the datasheet mentioned nothing about thermal shutdown.

If that is true, shorting the current sensing resistor may lead to permanent damage to the chip.
 
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millwood

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Matttcattt said:
how can 0.01 ohms not cause damage, but 0 ohms can?
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the trigger seems to be a Vbe junction, per the TI schematics. that is confirmed by the formula used to calculate the current sensing resistor:

Rcl=0.8/Icl-0.06 (or 0.02, depending which side of the cycle you are on).

so a 0.01ohm resistor will limit the output current to 11A - 26A; while a 0phm resistor will limit the output current to 13A - 40A.

as you can tell, if the current is large enough, it will make a significant voltage drop on a smaller resistor. more detailed infor can be found in a TI AN as well.

the datasheet for 549 seems to indicate that it uses a different protection mechanism.
 
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