Author Topic: Component Suggestions needed for SEPIC controller  (Read 754 times)

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Offline DarrellDTopic starter

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Component Suggestions needed for SEPIC controller
« on: December 09, 2018, 10:19:00 pm »
Been searching Digikey, Mouser, TI, STmicro, and Youtube for information on controller selection, but coming up more and more confused. I'm trying to find a controller for a power circuit with the smallest possible footprint (SOT-23-8). I have working components in hand, but can not find the components on the web...  |O |O

Vin = 3.4-25.2
Vout = 5
Imax = 2-3A

From the research I have done I am led to believe that a SEPIC or Buck-Boost controller would be needed. If anyone has a better solution, please teach me or point me in a direction I can gain better info? 
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Offline T3sl4co1l

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Re: Component Suggestions needed for SEPIC controller
« Reply #1 on: December 10, 2018, 02:12:20 am »
Any boost/flyback controller that operates over that range will do.  SEPIC is the same dynamics as buck-boost, specifically.

If you need a reasonably solid output current limit, you may want to add a secondary current sense / error amp and feed it back to the first error amp.  Since, the built in current limit (which is typically peak current mode, plus slope compensation so it's kind of sloppy to begin with) has to be set for the minimum input voltage (maximum input current), it can deliver a shitton more output current at full input voltage.

Just last week I did one with TPS40210, 8-40V input and 12V output.  The startup voltage on this one isn't quite low enough so you'll have to keep shopping around.

If you want the controller, with switch, and any other extras, to be near the footprint of a SOT-23, you're going to need CSPs, full stop.

Tim
Seven Transistor Labs, LLC
Electronic design, from concept to prototype.
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Offline DarrellDTopic starter

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Re: Component Suggestions needed for SEPIC controller
« Reply #2 on: December 10, 2018, 11:13:51 pm »
Thanks for the info, Tim!

After some thinking, and a little more reading I came to realize that the current of the controller does not matter to much as it is only for the Mosfet. The current limitation of the circuit is derived from the Fet and Inductor/s.. correct me if I'm wrong, but I think something like a LM3488 would suffice just fine?
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Offline T3sl4co1l

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Re: Component Suggestions needed for SEPIC controller
« Reply #3 on: December 11, 2018, 12:51:28 am »
Yes, that looks good.

Tim
Seven Transistor Labs, LLC
Electronic design, from concept to prototype.
Bringing a project to life?  Send me a message!
 
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