Confidential

Datasheet Version 1.2

Oct 8

14

OPERATION TIMING CHART

A capacitor on the VLDO pin begins charing after EN is turned-on. Once the VIN voltage reaches about 7.5V(See

UVLO specification), the internal UVLO is released. The MAP3249 checks the initial open FB(s) and excludes

corresponding FB(s) from headroom control before internal PG signal is set up. The unused FB(s) must be

connected to GND. Internal controller starts boosting with first PWM input and performs soft-start. After soft-start is

end or during soft-start period, the output voltage is boosted up to regulation voltage(total forward voltage of LED

bar + FB Voltage) without touching OVP level and the controller performs headroom control.

The MAP3249 boosts the output voltage only in condition that VIN is applied and EN, PWM and ADIM is turned-on. And

there is no limitation with regard to turn-on sequence. But in case that VIN(input voltage of booster) is applied lastly after

EN, PWM and ADIM is turned-on, the start-up current is increased because the output voltage is boosted from 0V.

If the PWM signal remains logic low for over than 16.4ms(1/fsw * 8192) at 500kHz boost switching frequency during

normal operation, the controller regards it as dim-zero condition. Because of discharge of output capacitor through the

OVP sensing resistors during the dim-zero time, the output voltage getting declined. The MAP3249 performs soft-start as

soon as PWM signal rises to boost the output voltage rapidly.

The controller stops switching right after EN is turned-off.