I am interested in LT4743.
According to data sheet : PWM Dimming Provide upto 3000:1 Dimming Raio.
I don't know what '3000' means.
I want to blink the LED according to input PWM frequency.
The frequency of PWM must be at least 4KHz.
I guess you mean LT3743, correct?
3000:1 mean the ratio between PWM on and PWM off time. You can modify both values (by still keeping PWM frequency constant) to adjust brightness of your light source.
As 4kHz results in 250us PWM periode, a division by 3000 ends up with a minimum pulse width of 83ns. This is too small and therefore 3000:1 is not feasible for your 4kHz PWM frequency.
But this was not for question, just for explanation.
4kHz is no problem for the PWM input, with the dutycycle of the PWM signal you can modify the brightness. Will you modify the PWM frequency or modify the PWM dutycycle?