SELF

HEATING

COMPENS.

EEPROM

+

LOGIC

ADC

+

LOGIC

BRIGHTNESS

0.8 ± 100%

8 STEP LOG

CORRECTION R

0 ± 200%

(AGEING COMP)

CURRENT R

0 ± 60mA

TEMP

SENSOR

PWM

GEN

R

G

B

S1_IN

PWM_R

12

12

12

12

12

5 MHz

8

8

ROUT

13

LP5520

www.ti.com

SNVS440B – MAY 2007 – REVISED MARCH 2016

Product Folder Links: LP5520

Submit Documentation Feedback

Copyright © 2007–2016, Texas Instruments Incorporated

Feature Description (continued)

(1)

PWM Brightness register control

Table 1. PWM Value Multipliers

MULTIPLIER

INTENSITY ( %)

0

0.008

0.8

1

0.016

1.6

2

0.031

3.1

3

0.063

6.3

4

0.125

12.5

5

0.250

25

6

0.500

50

7

1.000

100

The brightness correction can be used for aging compensation or other fine-tuning. There is an 8-bit correction

register for each output. The PWM value obtained from the memory is multiplied by the correction value. The

default correction value is 1. Correction range is from 0 to 2 and the LSB is 0.78% (1/128).

Shown complete only for red channel

Figure 16. LED Control Principle

7.3.2.3 LED PWM Control

The PWM frequency can be selected of two alternatives, slow and fast, with the control bit <pwm_fast>. The

slow frequency is 1.2 kHz. In the fast mode the PWM frequency is multiplied by 16, and the frequency is 19.2

kHz. Fast mode is the default mode after reset. The single pulse in normal PWM is split in 16 narrow pulses in

fast PWM. Higher frequency helps eliminate possible noise from the ceramic capacitors and it also reduces the

ripple in the boost voltage. Minimum pulse length is 200 ns in both modes.

The PWM pulses of each output do not start simultaneously in order to avoid high current spike. Red starts in the

beginning of the PWM cycle, Green is symmetric with the cycle center and Blue ends in the end of the cycle. For

PWM values less than 33% for each output, the output currents are completely non-overlapping. With higher

PWM values the overlapping increases.