LP55231 datasheet(11/59 Pages) TI2

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LP55231

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SNOSCR5D – MARCH 2013 – REVISED DECEMBER 2016

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7.3 Feature Description

7.3.1 Programming

The LP55231 provides flexibility and programmability for dimming and sequencing control. Each LED can be

controlled directly and independently through the serial bus, or LED drivers can be grouped together for pre-

programmed flashing patterns.

The LP55231 has three independent program execution engines, so it is possible to form three independently

programmable LED banks. LED drivers can be grouped based on their function so that, for example, the first

bank of drivers can be assigned to the keypad illumination, the second bank to the funlights, and the third group

to the indicator LED(s).

Each bank can contain 1 to 9 LED driver outputs. Instructions for program execution engines are stored in the

program memory. The total amount of the program memory is 96 instructions, and the user can allocate the

memory as required by the engines.

7.3.2 LED Error Detection

The LP55231 has built-in LED error detection. Error detection does not only detect open and short circuit, but

provides an opportunity to measure the VFs of the LEDs. The test event is activated by a serial interface write,

and the result can be read through the serial interface during the next cycle. This feature can also be addressed

to measure the voltage on the VDD, VOUT, and INT pins. Typical example usage includes monitoring battery

voltage or using INT pin as a light sensor interface.

7.3.3 Energy Efficiency

When charge-pump automatic mode selection is enabled, the LP55231 monitors the voltage over the drivers of

D1 to D6 so that the device can select the best charge-pump gain and maintain good efficiency over the whole

operating voltage range. The red LED element of an RGB LED typically has a forward voltage of about 2 V. For

that reason, the outputs D7, D8, and D9 are internally powered by VDD, since battery voltage is high enough to

drive red LEDs over the whole operating voltage range. This allows the driving of three RGB LEDs with good

efficiency because the red LEDs do not load the charge pump. LP55231 is able to automatically enter power-

save mode when LED outputs are not active, thus lowering idle current consumption down to 10 µA (typical).

Also, during the downtime of the PWM cycle (constant current output status is low), additional power savings can

be achieved when the PWM power-save feature is enabled.

7.3.4 Temperature Compensation

The luminance of an LED is typically a function of its temperature even though the current flowing through the

LED remains constant. Since luminance is temperature dependent, many LED applications require some form of

temperature compensation to decrease luminance and color purity variations due to temperature changes. The

LP55231 has a built-in temperature-sensing element, and PWM duty cycle of the LED drivers changes linearly in

relationship to changes in temperature. User can select the slope of the graph (31 slopes) based on the LED

characteristics (see Figure 13). This compensation can be done either constantly, or only right after the device

wakes up from powersave mode, to avoid error due to self-heating of the device. Linear compensation is

considered to be practical and accurate enough for most LED applications.

Compensation is effective over the temperature range

−40°C to +90°C.

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