ADPA888BI Circuit Note

Dear Sir,

We have few questions about reference circuit and hope to get your kindly help.

a. Why needs 5V boost to 6V for VLED ? we can not direct input 5V ? 

b. What is the reason that the circuit needs using three heating resistor ? it there dimensions for reference ? 

c. In the circuit note, +6V is for VLED3(IR) ? it looks different with ADPD188BI datasheet.  

  

Thanks for support. 

Regards,