Hello,
We are doing a 6W LED flasher
Spec of Buckboost LED flasher:
Vin = 10-30V
LEDs = Oslon SSL, white
9 LEDs in series
I(LED) = 500mA when ON
Flash duty = 300ms OFF, 80ms ON, 40ms OFF, 80ms, ON….repeatedly.
No dimming required.
No electrolytic capacitors.
Rise time of LED current with LM3421:
I worked through the Bode Plots as per the LM3421 datasheet. I get Ccmp = 270nF.
This will give a long start-up time of 10ms.
We will flash the LEDs ON and OFF with the nDim pin (the PWM dimming pin).
We are wondering if the Ccmp voltage will be “frozen” at the level when the LEDs were ON whilst the nDim pin is taken low?…or will the Ccmp capacitor be allowed to discharge when we are in the Flash_OFF state?
The worst thing would be if the Ccmp pin voltage rose when the nDim pin was taken low for the 340ms Flash_OFF interval.
Feedback loop measurement:
We wish to measure the feedback loop with an AP300 frequency analyzer, (gain & phase margin) in addition to having gone through the calculation as per the LM3421 datasheet.
Please advise on how to do the signal injection for the LM3421 based buckboost LED driver?
