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I want to clarify the statement on LM2596 Datasheet.
It states one of its feature is Ensured 3A Output Load Current.

My question is related to the Adjustable version of LM2596
Vin: 4.5V-40V
Vout: 3.3V-37V

Does the above statement means:
No matter what voltage the input is (as long it is still in Vin range and higher than Vout), the LM2596 will still regulate with 3A output load current?

Extreme cases:
Vin: 40V and Vout: 3.3V, and
Vin: 40V and Vout: 37V
Can LM2596 regulate both cases with 3A output load current? If not, please provide me info or chart that show varying load current based on Vin and Vout.

Side notes: My reason to ask these question is because I think LM2596 should have max power rating (I can't find one yet from Datasheet), thus 37V@3A would be more than 100W. And I think the power is too big for such small IC.

Thanks for your time!

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2 Answers 2

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... 37V@3A would be more than 100W.

Yes, but that's what your load would have to deal with. The IC only has to handle the losses when stepping down the voltage. Figure 5 gives the efficiency with a 3A load, and higher output voltages result in higher efficiency.

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  • \$\begingroup\$ Ok. So, from that Figure 5, can I conclude that LM2596 can regulate Vin 40V to Vout 3.3V with 3A load current? \$\endgroup\$
    – arsenalist
    Sep 25, 2015 at 5:54
  • \$\begingroup\$ Yes, while burning about 3.7W. \$\endgroup\$ Sep 25, 2015 at 5:56
  • \$\begingroup\$ Sorry for my ignorance, how do you get 3.7W? \$\endgroup\$
    – arsenalist
    Sep 25, 2015 at 6:02
  • \$\begingroup\$ The 3.3V curve is at about 73% with a Vin of 40V. 3.3V⋅3A⋅(1/.73−1)\$\approx\$3.66W \$\endgroup\$ Sep 25, 2015 at 6:03
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It's a switching power supply, the power it dissipates is relatively low. And if you step down from 40V to 3V, the duty cycle is very low, so most losses will be on the diode, reducing the IC power even more.

3A means that the switch inside and IC can hold it and maximum duty cycle is 100% or so. Hence, they will provide as much power as you need.

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