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For a small project, I would like to use 8 LEDs in series. Each LED has a Vf of 3.3 V. My input voltage is 3.3 VDC.

I plan to use the AP5724 LED driver.

The datasheet has an example of a circuit using 6 LEDs. I tried asking the manufacturer but I got no response.

Can the AP5724 drive 8 LEDs?

ocrdu
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Ariel Narboada
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    You'll be limited by the duty cycle. 8x higher voltage is 1-1/8 = 87.5% The min spec is 86% which can't do it, but the typical spec is 90%, which can do it. So probably a lot of chips will do it, but they won't guarantee it. – user1850479 Nov 02 '22 at 03:32

1 Answers1

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Can an AP5724 drive 8 LEDs?

Yes, you can drive 8 LEDs. The output voltage is limited to about 31V by the OVP pin. So your LED forward voltages must sum to less then the OVP value.

8*3.3V -> 26.4 + Vfb -> 26.5V

This appears to give you plenty of margin before OVP triggers.

You may have to set slightly less current depending on the inductor value you use. The 5 Ohm Rset value shown give 20mA LED current in the string. The 1uf cap also needs to be rated at >31V.

Jack Creasey
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  • thanks, Jack. follow-up question: would this driver work if it drives 2 parallel 8-LED strings? each string will have 15mA, so total of 30mA. – Ariel Narboada Nov 02 '22 at 04:52
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    No, I'd suggest you could not drive two strings at that current. Your total input power should be less than 1.5W @5V IMO. Something close to 18mA would work ....so just 9nA per string. – Jack Creasey Nov 02 '22 at 14:58