LP55231 datasheet(15/59 Pages) TI2

15 / 59 page

0,0

64,0

128,0

192,0

256,0

DIMMING CONTROL (DEC)

100,0

80,0

60,0

40,0

20,0

0,0

128

192

256

100

8-BIT CURRENT

SETTING

0 mA TO 25.5 mA

12-BIT PWM

PATTERN

CONTROL

0% TO 100 %

TIME

PWM FREQUENCY = 312 Hz

LP55231

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SNOSCR5D – MARCH 2013 – REVISED DECEMBER 2016

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Feature Description (continued)

7.3.6 LED Driver Operational Description

7.3.6.1 Overview

LP55231 LED drivers are constant current sources. Output current can be programmed by control registers up to

25.5 mA. The overall maximum current is set by 8-bit output current control registers with 100-μA step size. Each

of the 9 LED drivers has a separate output current control register.

The LED luminance pattern (dimming) is controlled with PWM (pulse width modulation) technique, which has

internal resolution of 12 bits (8-bit control can be seen by user). PWM frequency is 312 Hz. See Figure 16.

Figure 16. LED Pattern and Current Control Principle

LED dimming is controlled according to a logarithmic or linear scale, see Figure 17. A logarithmic or linear

scheme can be set for both the program execution engine control and direct PWM control. Note: if the

temperature compensation is active, the maximum PWM duty cycle is limited to 50% at 25°C. This is required to

allow enough headroom for temperature compensation over the whole temperature range

−30°C to +90°C.

Figure 17. Logarithmic vs Linear Dimming

7.3.6.2 Powering LEDs

The LP55231 is very suitable for white LED and general purpose applications, and it is particularly well suited to

use with RGB LEDs. The LP55231 architecture is optimized for use with three RGB LEDs. Typically, the red

LEDs have forward voltages below 2 volts, thus red LEDs can be powered directly from VDD. In the LP55231 D7,

D8, and D9 drivers are powered from the battery voltage (VDD), not from the charge-pump output. D1 to D6

drivers are internally connected to the charge-pump output, and these outputs can be used for driving green and

blue (VF = 2.7 V to 3.7 V typical) or white LEDs. Of course, D7, D8, and D9 outputs can be used for green, blue

or white LEDs if the VDD voltage is high enough.

An RGB LED configuration example is given in the Typical Applications.

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