I don’t know it exactly as well but I found this:
High efficiency LED driver. All modes (except moon) are implemented without PWM , linearly, using a current source based on a MOSFET transistor, which in practice means 1.5-2x longer work time at low brightness levels compared to classic PWM drivers keying the AMC7135 current sources or transistor.
The controller has a turbo mode (current 8A), about 3200lm for 4x XP-L, implemented by a MOSFET transistor, with hardware stabilization of the upper current value.
Parameters:
• linear5A current source implemented on MOSFET RDSon 0.95 mΩ transistor controlled from ATtiny85V with feedback
• modes (brightness levels) implemented without PWM, with maximum LED efficiency
• diameter 17mm - flashlight standard
• supply voltage range 2.8-4.5V
• power supply: 1x 18650 Li-ion cell, preferably without protection
• maximum LED current 5A, in turbo mode 8A (limited by the capacity and battery charge level)
• full current stabilization at Vf LED + 0.1V supply voltage, with the latest brand cells to be used 80-85% Li-ion capacity
• no PWM , flicker, noiseless operation
• total efficiency 2.8-4.5V power range is over 90%
and