The PAM2804 is a step-down constant current LED driver. When the input voltage is down to lower than LED forward voltage, then PAM2804 goes into LDO mode.
Datasheets by Manufacturer
PAM2800 — Power Analog Micoelectronics — High Power White LED Driver
PAM2803 — Power Analog Micoelectronics — 3W High Power White LED Driver
PAM2801 — Power Analog Micoelectronics — 1W High Power White LED Driver