RT4539A

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DS4539A-01

December 2022

26

PWM Sample Rate

In DC/Mixed/Mixed-26kHz, the digital modulator need sample rate to calculate average current based on PWM input

frequency. The user must set 0x07h [7: 5] to coordinate sample rate for different PWM input frequencies. More

setting details are shown in Table 13.

Table 13. PWM Sample Rate

Address Bit

Name

Default Value

Description

R/W

07h

[7:

5]

PWM sample rate

auto detection

(B000)

B000: auto detection

B001: 0.5MHz

B010: 1MHz

B011: 2MHz

B100: 4MHz

B101: 8MHz

B110: 16MHz

B111: 16MHz

R/W

Note :

PWM Input Frequency Range PWM sample rate 07h[7:

5]

PWM frequency fixed

B000 (auto detection)

PWM ≤ 61Hz

B001 (0.5MHz)

61Hz < PWM ≤ 122Hz

B010 (1MHz)

122Hz < PWM ≤ 244Hz

B011 (2MHz)

244Hz < PWM ≤ 488Hz

B100 (4MHz)

488Hz < PWM ≤ 977Hz

B101 (8MHz)

977Hz < PWM

B110 (16MHz)

B111 (16MHz)

Soft-Start Time Control

The RT4539A intergrades a soft-start time control to prevent brightness change suddenly during power-on. The

soft-start time control can be set by the I2C interface. More setting details are shown in Table 14.

Table 14. Soft Start Time Control

Address

Bit

Name

Default Value

Description

Resolution

R/W

08h

[1: 0]

Soft-Start

Time Control

1µs

(B00)

Soft start time control

B00: 1µs

B01: 16µs

B10: 128µs

B11: 512µs

--

R/W

Soft-start time can be controlled by address 0x08h [1: 0]. There are four times to adjust range from 1µs to 512µs.

The soft-start time function is only enabled during power-on. When the Soft-start command is below B00, the

brightness time of per step will be kept at 1µs. This function can guarantee the highest of Soft-start time is 512µs.