Buck Boost converter

[DLesl]

Dear All Have a nice Day

I am new to this forum

I am working with TPS63060 buck boot converter

it input voltage is 2.5 to 12v and output is 2.5v to 8 v But I need 

input 2.5v to 15v and output voltage 2.5 to 15v converter 

usage 

Line follower robot with two DC motor

DC motor 

6v 300rpm ( N20 Type)

I am planing to run robot at constant voltage even battery voltage drooped 4v 

Please advice

Dayan