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I have a question about the following LED drivers:

FAN5331, datasheet http://www.mouser.com/ds/2/149/FAN5331-92198.pdf

FAN5333, datasheet https://www.onsemi.com/pub/Collateral/FAN5333B-D.pdf

They look very similar apart from the output voltage, which is about 20V for 5331 and 30V for 5333. From 5333 datasheet I can see that the SHDN pin can be used for PWM dimming control, but there is no such information in 5331 datasheet.

Can I still use FAN5331 with an external PWM signal, similar to FAN5333 ?

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  • \$\begingroup\$ Both datasheets tell you how the output behaves when the /SHDN pin goes high. Compare and contrast. \$\endgroup\$
    – CL.
    Apr 6, 2019 at 17:55
  • \$\begingroup\$ Both datasheets say the same thing - HIGH enables the device, LOW - disables it. Maybe I am asking a stupid question, but there is nothing about PWM dimming in 5331 datasheet. \$\endgroup\$
    – hanni76
    Apr 6, 2019 at 18:23

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Yes, you could. They stated it themselves that they are pulse-width modulated (PWM) current-mode boost converter if you read it at the Circuit Description section.

FAN5333 use internal lower shunt resistor of \$30\,\mathrm{m}\Omega\$, while FAN5331 use \$50\,\mathrm{m}\Omega\$ . FAN5333A/B use lower internal voltage reference of typical \$0.11\,\mathrm{V}\$ or \$0.31\,\mathrm{V}\$ , while FAN5331 \$1.23\,\mathrm{V}\$ . Although small, may affect your design a little.

The biggest difference in my opinion would be the soft start circuitry of FAN5331 which may affect your PWM output current and voltage. You need to test them both to make sure how they behave in your specific application as the data given in the datasheet are limited.

FAN5331 Circuit Description

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An internal soft start circuitry minimizes in-rush currents. The timing of the soft start circuit was chosen to reach 95% of the nominal output voltage within maximum 5mS following an enable command when VIN = 2.7V, VOUT = 15V, ILOAD = 35mA and COUT (EFFECTIVE) = 3.2µF.

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  • \$\begingroup\$ Thank you so much. The soft-start circuit seems to give some delay, I think it shouldn't be a problem. \$\endgroup\$
    – hanni76
    Apr 6, 2019 at 19:30
  • \$\begingroup\$ @hanni76 Yes, thus also implies as an inrush current limiter. Report back if you got any problems. \$\endgroup\$
    – Unknown123
    Apr 6, 2019 at 19:33

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