LP8556 datasheet(18/63 Pages) TI1

18 / 63 page

25%

100%

Max current is set with CURRENT and CURRENT_MAX EPROM bits

or CURRENT and CURRENT_MAX EPROM bits and RISET resistor

25%

50%

100%

PURE CURRENT CONTROL

(PWM_TO_I_THRESHOLD = 0000b)

BRIGHTNESS

50%

25%

50%

100%

PWM CONTROL

(PWM_TO_I_THRESHOLD = 1111b)

BRIGHTNESS

Max current is set with CURRENT and CURRENT_MAX EPROM bits

or CURRENT and CURRENT_MAX EPROM bits and RISET resistor

100%

LP8556

SNVS871I – JULY 2012 – REVISED MARCH 2016

www.ti.com

Product Folder Links: LP8556

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8.3.2.5 Output Dimming Schemes

The LP8556 device supports three types of output dimming control methods: PWM Control, Pure Current Control

and Adaptive Dimming (Hybrid PWM and Current) Control.

8.3.2.5.1

PWM Control

PWM control is the traditional way of controlling the brightness using PWM of the outputs with the same LED

current across the entire brightness range. Brightness control is achieved by varying the duty cycle proportional

to the input PWM. PWM frequency is set either using an external set fesistor (RFSET) or using the PWM_FREQ

EPROM field. The maximum LED current is set by using an external set Resistor (RISET), CURRENT, and

CURRENT_MAX EPROM bits. PWM frequency can also be set by simply using the CURRENT and

CURRENT_MAX EPROM bits.

NOTE

The output PWM signal is de-coupled and generated independent of the input PWM signal

eliminating display flicker issues and allowing better noise immunity.

Figure 8. PWM Only Output Dimming Scheme

8.3.2.5.2

Pure Current Control

In Pure Current Control mode, brightness control is achieved by changing the LED current proportionately from

maximum value to a minimum value across the entire brightness range. Like in PWM Control mode, the

maximum LED current is set by using an external set Resistor (RISET), CURRENT, and CURRENT_MAX EPROM

bits. The maximum LED current can also be set by just using the CURRENT and CURRENT_MAX EPROM bits.

Current resolution in this mode is 12 bits.

Figure 9. Pure Current or Analog Output Dimming Scheme

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