LED171596ARSLR datasheet(14/153 Pages) TI1

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LEDxx PWM Brightness = ledxx_bri

PWM input duty cycle

LEDxx PWM Brightness = ledxx_bri

master _ bri

LED(XX)

ISET

750

ledxx_cur[7 : 0]

255

LED171596A

SNVSAY2 – OCTOBER 2017

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7.3.2 LED Current Sinks

7.3.2.1 LED Output Current Setting

The RISET resistor is used to set the maximum LED current for all LED driver outputs. The LEDXX_CUR[7:0]

registers are used to individually adjust the current of each from zero to the maximum. Equation 1 is used to

calculate the current setting of an individual LED in this mode.

(1)

For example, a 12.5-kΩ RISET results in a 60-mA maximum peak current. Each LEDXX_CUR LSB adjusts the

individual LED current by 235–µA steps. Smaller individual current adjustment steps are achieved when using a

lower maximum peak current (larger RISET value). For example, a 25-kΩ RISET results in a 30-mA maximum

peak current and 118-µA steps per LEDXX_CUR LSB.

7.3.2.2 LED PWM Frequency

The LED171596A supports 10-kHz or 20-kHz pwm output frequency. The pwm frequency is configured using the

CONFIG_PWM register bit [4]. An internal 40-MHz oscillator is used for generating PWM outputs. When

CONFIG_PWM register bit 4 is high the reference clock is divided by 2.

7.3.2.3 LED Driver Group Turnon Delay

The 24 LED current sinks turn on in four different groups with a programmable delay between groups. The delay

is configured using the PWM_PHASE_SHIFT_CONFIG register bits [1:0] to select from 0, 1, 2, or 3 reference

clock delays. This delay reduces inrush currents and reduces maximum LED on-time. The first group consists of

LED0, 4, 8, 12, 16, and 20 which turn on with no delay and turn off up to 3 clocks before the maximum on-time.

The second group consists of LED1, 5, 9, 13, 17 and 21, which turn on and off up to 3 clocks after the first

group. The third group consists of LED2, 6, 10, 14, 18 and 22, which turn on and off up to 3 clocks after the

second group. The fourth group consists of LED3, 7, 11, 15, 19, and 23, which turn on and off up to 3 clocks

after the third group.

7.3.3 Brightness Control

The LED171596A supports individual brightness control for each LED through individual PWM duty cycle control

of LED0...LED95 via I2C/SPI registers. A master brightness register or PWM input is multiplied with each

individual (LEDXX_BRI[8:0]) brightness register to allow control of every LED at once.

7.3.3.1 Brightness Control Signal Path

There are several methods to control the brightness level of each LED:

7.3.3.1.1

Master Brightness Control Method

Using master brightness control through master_bri register or PWM input (selectable by register bit

enable_pwm_detector – PWM input is available only in I2C mode). Master brightness control affects all LEDs

simultaneously. Master brightness can change the LED brightness immediately or smoothly using the optional

sloper block. Master brightness change requires a single write transaction so bus traffic is very low. A LATCH

command is required if Master Brightness is controlled by register write (master_bri). The PWM input control can

change the master brightness immediately without need of a LATCH command.

The individual LED PWM duty cycle is calculated using Equation 2 and Equation 3:

When enable_pwm_detector = 0:

(2)

When enable_pwm_detector = 1:

(3)

LED171596ARSLR Datasheet(PDF) 14 Page - Texas Instruments

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