RT4539A

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is a registered trademark of Richtek Technology Corporation

DS4539A-01

December 2022

www.richtek.com

17

time

PWMI

time

ILED

ILED

Max

0

50%

25%

75%

25%

75%

50%

50%

10%

Figure 3. Mixed Mode Dimming

*During DC / Mix Mode dimming, the behavior of PWM Duty 100% and 0% ILED are shown in the following

Figure.

PWM

ILED

DAC

When PWM changes from Low to High the

internal counter will restart 20ms counting

20ms

LED current changes from

0mA to 100% ILED setting.

00

FFF

PWM keeps high 20ms, DAC

code changes to 1FFh.

00

20ms

Figure 4. Duty 100% and Duty 0% ILED behavior.

Switching Frequency and LX Slew Rate Control

In order to improve EMI performance, the boost converter embeds switching frequency, spread spectrum and LX

edge rate control feature, and these functions are programmable by the I2C interface. The more detailed settings

are shown in Table 3 and Table 4.

Table 3. Switching Frequency and LX Slew Rate Setting

Address

Bit

Name

Default Value

Description

R/W

00h

[6: 5] LX Edge Rate Control

200% (B11)

B00: 25%

B01: 50%

B10: 100%

B11: 200%

R/W

[7]

Spread Spectrum

w/o (B0)

B0: w/o

B1: w/i

R/W

01h

[3: 0]

Boost Switching

Frequency

600kHz

(0x07h)

0x00h ~ 0x04h: 300kHz

0x0Fh: 1600kHz

(Table)

R/W

If the switching frequency command is below to register 0x01, the switching frequency is from 300kHz to 1.6MHz.