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LM3409: The inductance and the switching frequency of LM3409
Could you provide a little more information? Do you mean they will pulse each LED on for only 1us to 2us? Or is this a minimum duty cycle during PWM dimming? If so what is the PWM dimming frequency? Are there any LED current ripple requirements?
In general when you pull EN high the current rise time is dictated by the voltages and the inductance by v=Ldi/dt. The v would be Vin-Vf. So in many cases 1 to 2us will not even reach the peak current value so switching frequency is irrelevant at such a small pulse width.
So this application is sort of on the edge of what you can do. Using that equation for example with the green the voltage differential is about 10V between Vin and Vf and with a 10uH inductor the current rise time would be 1us per amp. So the current rise time to 0.36A would be 360ns. The best thing to do then would be to try and set the switching frequency high, around 1MHz to 2MHz (use a very low Qg FET for high Fsw, Rds(on) and losses are likely negligible here). Then use the minimum inductor value calculated to make sure the rise time is as fast as possible BUT without exceeding the 211ns minimum on-time of the device.
As a side note if the EN pin is low long enough for VCC to discharge the device will go into low power shutdown mode and will not respond fast enough on the next pulse. I would use the UVLO pin for the pulse. It behaves exactly the same except VCC will not discharge and the device will stay active for a fast response.
