LM3409HV: LM3409HV Input and Output capacitor

Hello Fenvi,

There should be some ceramic at the input due to the impedance and the switching frequency.  Electrolytic can be used for bulk storage if needed.  This depends on the source impedance, load steps/PWM dimming.

Are you PWM dimming by the PWM pin or by shunt FET dimming?  If you are using EN pin dimming you can use it for the output capacitance, some ceramic will filter the switching frequency, the electrolytic the PWM frequency.  If you are shunt FET dimming you do not want much if any output capacitance since it becomes switching loss.

It depends on what you want to do with the design and how the system is designed.

Is this 10 strings at approximately 75W each or total (assuming Vf = 3V), 75W versus 750W?

Questions:

EN pin dimming or shunt FET dimming?

Switching frequency?  Is there a range?

75W total or 750W total assumiing 3V Vf?  Or something else?

Power source for this is located?  Wires?  Etc?

Are the PWM signals set up to be synchronized out of phase or something else?

Concern of using ceramic and electrolytic?

Best Regards,

thanks for your reply,

i answer all your question below :

EN pin dimming or shunt FET dimming?

EN pin dimming

Switching frequency?  Is there a range?

400khz

75W total or 750W total assumiing 3V Vf?  Or something else?

39V x 2.5A  (97.5W) per channel and at all there are 10 channel (975W) on same pcb.

Power source for this is located?  Wires?  Etc?

Power source is closed but not on the pcb (connected by wires) on other pcb and those cards are on backplane 

Are the PWM signals set up to be synchronized out of phase or something else?

all PWM signals are synchronized at same time.

Concern of using ceramic and electrolytic?

i use ceramic capacitors at each output (2.2uF)

for input i use  one 33 uF electrolytic capacitor and one 2.2uF ceramic capacitor for each channel

At the input of the pcb i use 220 uF electrolytic capacitor.

thanks