LP85571 datasheet(14/49 Pages) TI2

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Curve

Shaper

Hybrid

PWM&I

Dimming

PWM

Gen

Brightness

CURRENT

PWM

MAXCURR

THRESHOLD

Input

VIN

LP8557

1.1 ” VOUT / VIN ” 11

VDD

CIN

COU

LED1

LED2

LED3

LED4

LED5

LED6

GNDs

ISET

FSET

2.7 V ± 5.5 V

7 V ± 28 V

PWM

VOUT

RFSET

RISET

LP8557, LP85571

SNVSA15B – DECEMBER 2013 – REVISED DECEMBER 2015

www.ti.com

Feature Description (continued)

Figure 24. Typical Application Circuit for Devices Configured With BRTMODE = 00

8.3.2.3 BRTMODE = 01b

With BRTMODE = 01b, the LED output current is controlled by the BRTHI/BRTLO registers. Before the output is

generated the BRTHI/BRTLO registers-based brightness code goes through the Curve Shaper block. Then the

code goes into the hybrid PWM & I dimming block which determines the range of the PWM and current control.

The outcome of the Hybrid PWM&I Dimming block is Current and/or up to 6 PWM output signals.

Figure 25. Brightness Data Path for BRTMODE = 01b

8.3.2.4 BRTMODE = 10b

With BRTMODE = 10b, the LED output current is controlled by the PWM input duty cycle and the BRTHI/BRTLO

registers. The PWM detector block measures the duty cycle at the PWM pin and uses it to generate PWM-based

brightness code. Before the code is multiplied with the BRTHI/BRTLO registers-based brightness code, it goes

through the curve shaper block. After the multiplication, the resulting code goes into the hybrid PWM & I dimming

block which determines the range of the PWM and Current control. The outcome of the hybrid PWM & I dimming

block is current or up to 6 PWM output signals.

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