TI-LP55231：9通道LED驱动器，I2C控制与高效率特性

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TI-LP55231是一款高度集成的LED驱动器，专为移动设备中的灯光应用设计，如智能穿戴设备或微型电子产品。它具有以下主要特点： 1. 多通道驱动能力：拥有9个独立的可编程输出通道，每个通道支持最大25.5mA的电流输出，具有8位的电流设置分辨率，能够实现精细的LED亮度控制。 2. 高效电荷泵：采用自适应1x/1.5x分数型电荷泵，能在2.7V至5.5V的宽广锂离子电池电压范围内工作，提供高达94%的效率，减少了能量损耗。 3. 无处理器控制运行：内置程序存储器，使得器件可以在没有外部微控制器干预的情况下独立运行，提高了系统的灵活性和响应速度。 4. I2C通信接口：具备I2C兼容的控制接口，方便与MCU或其他微控制器进行数据交换，具有四个可选地址引脚，便于多个LP55231器件之间的协同工作。 5. 中断功能：INT引脚可以检测到照明序列结束，从而通过中断通知处理器，便于处理任务的调度和管理。 6. 软启动和保护：电荷泵模块具备软启动功能，防止瞬间大电流冲击，同时具有过流和短路保护机制，确保系统安全稳定。 7. 内置测试功能：器件内置LED测试电路，方便用户诊断和维护。 8. 低功耗模式：在待机状态下，典型电流消耗仅为200nA，当IVDD降至10μA时，进入自动节能模式，进一步节省电力。 9. 电压适应性：用户可以根据LED正向电压的具体情况调整电荷泵增益，以优化在不同电压范围内的性能。 10. RGBLED应用：特别适合RGBLED的控制，其中D7、D8和D9可以直接由VIN供电，简化了电路布局。 TI-LP55231是一款集成了高性能、低功耗和易于集成特性的LED驱动器，为移动设备的照明系统提供了可靠而灵活的解决方案。

CHARGE PUMP

1X/1.5X

0.47 PF

OUT

1 PF

VOUT

C1+ C1- C2+

C2-

D/A

PROGRAM

MEMORY

50H TO 6FH;

96 INSTRUCTIONS

PWM PATTERN

GENERATOR

PWM PATTERN

GENERATOR

PWM PATTERN

GENERATOR

12 BIT PWM

PATTERN

CONTROL

8 BIT

MAXIMUM

CURRENT

CONTROL

IDAC AND

HIGH SIDE

LED DRIVERS

SCL

SDA

CLK

INT

ASEL1

ASEL0

TRIG

SERIAL

DATA

CTRL

REG

POR

THERMAL

SHUTDOWN

CLK

DET

1.25 MHz

OSC

BIAS

VREF

CONTROL

GND

1 PF

VDD

TEMP

COMP

LED ERROR DETECTION

LP55231

ZHCSD18A –MARCH 2013–REVISED OCTOBER 2014

www.ti.com.cn

7 Detailed Description

7.1 Overview

The LP55231 is a fully integrated lighting management unit for producing lighting effects for mobile devices. The

LP55231 includes all necessary power management, high-side current sources, temperature compensation, two-

wire control interface and programmable pattern generators. The overall maximum current for each driver is set

by an 8-bit register.

The LP55231 controls LED luminance with a pulse width modulation (PWM) scheme with a resolution of 12 bits.

Also, the temperature compensation is done by PWM.

7.2 Functional Block Diagram

LP55231

www.ti.com.cn

ZHCSD18A –MARCH 2013–REVISED OCTOBER 2014

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 V

s 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 don't 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 (typ.). Also, during

the "down time" of the PWM cycle (constant current output status is low), additional power savings can be

achieved when the PWM Powersave 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.

REG

1.5X

1.5 x V

OUT

-25 0 25 50 75

TEMPERATURE °C

100

PWM OUTPUT %

MAXIMUM

SLOPE VALUE

MINIMUM

SLOPE VALUE

COMP.

LP55231

ZHCSD18A –MARCH 2013–REVISED OCTOBER 2014

www.ti.com.cn

Feature Description (continued)

Figure 13. Temperature Compensation Principle

7.3.5 Charge Pump Operational Description

7.3.5.1 Overview

The LP55231 includes a pre-regulated switched-capacitor charge pump with a programmable voltage

multiplication of 1 and 1.5x. In 1.5x mode, by combining the principles of a switched-capacitor charge pump and

a linear regulator, a regulated 4.5 V output is generated from the Li-Ion input voltage range. A two-phase non-

overlapping clock generated internally controls the operation of the charge pump. During the charge phase, both

flying capacitors (C1 and C2) are charged from input voltage. In the pump phase that follows, the flying

capacitors are discharged to output. A traditional switched-capacitor charge pump operating in this manner will

use switches with very low on-resistance, ideally 0Ω, to generate an output voltage that is 1.5x the input voltage.

The LP55231 regulates the output voltage by controlling the resistance of the input-connected pass-transistor

switches in the charge pump.

7.3.5.2 Output Resistance

At lower input voltages, the charge pump output voltage may degrade due to effective output resistance (R

OUT

) of

the charge pump. The expected voltage drop can be calculated by using a simple model for the charge pump

illustrated in Figure 14 below.

Figure 14. Charge Pump Output Resistance Model

The model shows a linear pre-regulation block (REG), a voltage multiplier (1.5x), and an output resistance

OUT

). Output resistance models the output voltage drop that is inherent to switched capacitor converters. The

output resistance is 3.5Ω (typ.), and it is a function of switching frequency, input voltage, flying capacitors’

capacitance value, internal resistances of the switches and ESR of the flying capacitors. When the output voltage

is in regulation, the regulator in the model controls the voltage V’ to keep the output voltage equal to 4.5 V (typ.).

With increased output current, the voltage drop across R

OUT

increases. To prevent drop in output voltage, the

voltage drop across the regulator is reduced, V’ increases, and V

OUT

remains at 4.5 V. When the output current

increases to the point that there is zero voltage drop across the regulator, V’ equals the input voltage, and the

output voltage is “on the edge” of regulation. Additional output current causes the output voltage to fall out of

regulation, so that the operation is similar to a basic open-loop 1.5x charge pump. In this mode, output current

results in output voltage drop proportional to the output resistance of the charge pump. The out-of-regulation

output voltage can be approximated by: V

OUT

= 1.5 x V

– I

OUT

x R

OUT

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