LT3745EUJ Просмотр технического описания (PDF) - Linear Technology

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LT3745EUJ

16-Channel 50mA LED Driver with Buck Controller

Linear Technology 

LT3745

OPERATION

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.

C1/EN

PWMCK

I(LED00)

1

tPD-PWM

REG = 0x002

tWH-PWM

2

3

tWL-PWM

3584

3585

4095

4096

1

2

I(LED01)

REG = 0xFFF

I(LED15)

REG = 0x000

PRECHG

TRACKING PHASE

PRECHARGING PHASE

3745 F04

Figure 4. Grayscale PWM Dimming and Precharging Signal Timing Chart

3745f

17

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