Datasheet

LT3745
17
3745f
Adaptive-Tracking-Plus-Precharging
Higher system efficiency and faster transient re-
sponse are two highly anticipated specifications in an
individually-modulated multi-channel LED driver chip.
The LT3745 uses a patent pending adaptive-tracking-
plus-precharging technique to achieve both of them
simultaneously.
Besides 16 internal grayscale PWM dimming signals,
the part also generates another internal precharging
signal PRECHG. As shown in Figure 4, the PRECHG
signal divides any grayscale PWM dimming cycle
into two phases: tracking phase when PRECHG = 0
and precharging phase when PRECHG = 1. During
each grayscale PWM dimming cycle – 4096 PWMCK
clock cycles, the PRECHG signal stays low for the first
3584 clock cycles (7/8 of the grayscale PWM dimming
period) and goes high for the rest 512 clock cycles (1/8
of the grayscale PWM dimming period). In the event of
all the LED channels being not
active (i.e., either fault
or off) before the 3585th PWMCK clock, the PRECHG
signal will go high immediately.
operaTion
Figure 4. Grayscale PWM Dimming and Precharging Signal Timing Chart
PWMCK 40964095 1 235841 2 3
C1/EN
I(LED00) REG = 0x002
REG = 0xFFF
TRACKING PHASE PRECHARGING PHASE
REG = 0x000
I(LED01)
t
WH-PWM
t
WL-PWM
t
PD-PWM
I(LED15)
PRECHG
3585
3745 F04