RT4539A

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DS4539A-01

December 2022

www.richtek.com

23

This equation is valid for I2C brightness codes between 1 and 2047. If Code is 0, the brightness will be disabled.

When address 0x07h is set B01 and linear mode is selected by address 0x03h, the I2C interface will transfer

code-to-current response with 12-bit resolution and target ILED is approximated by following equation:

ILED = 6.105uA×I2C code

(forcodes≥0) @ILEDmax=25mA

This equation is valid for I2C brightness codes between 0 and 4095. If Code is 0, the brightness will be disabled.

Slope Time

ILED_t1

ILED_t0

t1

t0

1. At time t0, the I2C Brightness code changes from 0x400 (1024d) to 0xFFF (4095d)

2. Mapping mode is set to linear

3. ILED_t0=6.105uA x 1024 =6.25mA

4. ILED_t1=6.105uA x 4095 =25.0mA

Figure 7.

LED Current with Advanced Brightness Control Selection “10”

When address 0x07h is set to B10, this mode is only for DC mode and linear mapping.

The target brightness code will be multiplied with the PWM duty cycle and I2C code. Moreover, resolution can

support up to 12 bits.

The target ILED is approximated by the following equation :

ILED = 6.105uA×I^2 C code×4095×PWM duty (for codes≥0 & PWM duty≠0% And 100%) @ILEDmax = 25mA

(Note 7)

Slope Time

ILED_t1

ILED_t0

t1

t0

1. At time t0, the I2C Brightness code changes from 0x400 (1024d) to 0xFFF (4095d)

2. At time t0 the PWM duty cycle change from 40% to 80%

3. Mapping mode is set to linear with DC mode

4. ILED_t0=6.105uA x 1024 x 0.4 =2.5mA

5. ILED_t1=6.105uA x 4095 x 0.8 =20.0mA

Figure 8

The following table is the critical condition for PWM Cycle setting. When PWM Duty = 0% or PWM Duty = 100%,

ILED will not consider I2C Code.