LT3474 LED DRIVER

Question

I would like to purchase led drivers( LT3474 ) for my project(Visible light communication) which is capable of accepting a pwm signal from a microcontroller. I just have a few questions. 
 1) How many LEDs in an array can I drive with a single led driver? 
 2) Can it receive a modulated signal from a micro-controller and switch on and off the LEDs depending the signal. And if there is no modulated signal on the pwm pin, will the led driver continue to drive the LEDs at DC? 
 
 This is for my undergraduate project and it would be lovely if you can clear my queries at the earliest. 
 
 Thank you.

KLawrence · Answer

1) As per page 1 of the datasheet: "LT3474-1 Drives LED Strings Up to 26V". This of course requires a higher input voltage given that LT3474 is a step down LED driver. 
 2) The LT3474 can be PWM dimmed by adding a low-side NMOS device at the bottom of the LED string, and applying a signal to the PWM pin of the device as well as the gate of the NMOS. If you want the device to be on at DC when the microcontroller is not sending a signal, then you will want to add a pull up resistor from the gate of the MOSFET to an external source high enough in voltage to fully enhance the NMOS.