LP8501 datasheet(17/51 Pages) TI1

17 / 51 page

0,0

64,0

128,0

192,0

256,0

DIMMING CONTROL (DEC)

100

128

192

256

8-BIT CURRENT

SETTING

0 mA TO 25.5 mA

12-BIT PWM

PATTERN

CONTROL

0% TO 100 %

TIME

PWM FREQUENCY = 312Hz

LP8501

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SNVS548D – SEPTEMBER 2008 – REVISED AUGUST 2013

Gain Change Hysteresis

Charge pump gain control utilizes digital filtering to prevent supply voltage disturbances (for example, the

transient voltage on the power supply during the GSM burst) from triggering unnecessary gain changes.

Hysteresis is provided to prevent periodic gain changes, which would occur due to LED driver and charge pump

voltage drops in 1x mode. The hysteresis of the gain change can be configured by the user; default setting is

factory programmable. Flexible configuration ensures that hysteresis can be minimized or set to desired level in

each application.

LED Driver Operational Description

Overview

The LP8501 LED drivers are constant current sources. Output current can be programmed with an I2C register

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. See table below for current control.

CURRENT bits

Output Current

00000000

0.0 mA

00000001

0.1 mA

00000010

0.2 mA

...

10101111

17.5 mA default setting

....

11111110

25.4 mA

11111111

25.5 mA

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 19.

Figure 19. LED Pattern and Current Control Principle

For LED dimming a logarithmic or linear scale can be applied — see the figure below (Figure 20). Logarithmic or

linear scheme can be set for both the program execution engine control and direct PWM control. By using a

logarithmic PWM scale, the visual effect looks linear to the human eye.

Figure 20. Logarithmic vs Linear Dimming

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