CN101883454B

CN101883454B - LED driving chip with single-line pulse control mode

Info

Publication number: CN101883454B
Application number: CN200910050874.7A
Authority: CN
Inventors: 张科; 李文宏
Original assignee: Fudan University
Current assignee: Fudan University
Priority date: 2009-05-08
Filing date: 2009-05-08
Publication date: 2014-06-11
Anticipated expiration: 2029-05-08
Also published as: CN101883454A

Abstract

The invention belongs to the technical field of a power management integrated circuit, and relates to a LED driving chip with a single-line pulse control mode. The LED driving chip comprises an enabling and logic control circuit, a reference voltage source, a digital-analogue converter and an MOS current driver, wherein the LED driving chip provides power to an LED array; the enabling and logic control circuit generates a control logic and algorithm of a corresponding working mode by adjusting the logic state of an input enabling signal EN; the reference voltage source provides a stable reference voltage to the system; the digital-analogue converter realizes the LED dimming function; and the MOS current driver generates a current to drive the LED. The LED driving chip can realize the functions of LED dimming, output current holding and shut-down, reduce the number of control pins of the chip and the number of off-chip elements and lower the use cost of a user according to a logic state of a single-line pulse input signal.

Description

A kind of LED driving chip with single-line pulse control mode

Technical field

The invention belongs to power management technical field of integrated circuits, be specifically related to a kind of design and realization of LED driving chip with single-line pulse control mode.

Background technology

Along with the whole world is for the attention increasingly of environmental protection and energy saving, market constantly increases the demand of energy-efficient electronics product, and power management IC importance is therein also constantly soaring.Environmental protection, power saving, the theory such as energy-conservation are constantly expanded LED technology and range of application thereof, and especially LED illumination has become the high-brightness LED the fastest application product of growing up.Following LED application trend will be backlight to large scale liquid crystal TV, automobile-used LED, large-scale panel, notebook computer, LED street lamp, indoor and outdoor lighting are decorated, or even home lighting market development.Along with the LED application such as indoor and outdoor lighting, auto bulb and LCD TV backlight driving emerge in multitude, LED 3C even 4C product all appeared huge commercial opportunities in one's mind, the numerous and confused layout L ED application market of numerous power supply IC manufacturer, sets up research and development strength, active development Related product scheme.

The characteristic requirements of LED drive IC is uniformity and the constancy of electric current output.LED drive IC need to be controlled one or plurality of LEDs, its luminosity be roughly linear proportional relation by the magnitude of current, therefore to make LED luminosity identical, must keep the LED magnitude of current that is joined together consistent.Because the slight change of electric current will affect brightness, this will be unacceptable for many application of LED.

In existing product solution, regulate the brightness of LED conventionally to have three kinds of methods: to use chip exterior SET resistance, adopt PWM control technology and linear regulation.The easiest LED brightness adjusting method is to adopt SET resistance outward in drive IC, and this method is relevant with the precision of off chip resistor, therefore can accurately control LED output current size, still has a lot of application in the product of the company such as Maxim, Fairchild.Although using chip exterior SET resistance is effective method, lacks flexibility.Adopt PWM control technology and linear regulation dynamically to control LED luminous intensity, particularly, in the particular application of some portable equipments, dynamically control LED luminous intensity and seem particularly important.

In the time that portable set starts or shut down, it is exactly one typical case application wherein that the gradual brightness of creating arenas formula illuminating effect changes.In the time starting, back facet current can progressively be amplified to lowest high-current value such as 20mA in a stepwise manner with the predefined time interval, in the time of shutdown, adopts contrary action progressively to reduce current value equally.By the control of microprocessor, can will possess the pwm signal of different frequency, deliver to LED drive circuit by I2C or I/O port and realize such effect.But the shortcoming of this method is to expend real-time processor resource, and need input/output interface and a large amount of external devices.

Single line control mode is only used a control line Digital Control LED, and clock cycle, saving universal input/output (GPIO) resource of microcontroller are exported, reduced to the light that flicker free is provided, for the portable application that uses less components and parts provides total solution, be subject to more and more users' favor.

Summary of the invention

The object of this invention is to provide a kind of LED driving chip with single-line pulse control mode, the present invention can, according to the different logic state that enables input end signal EN, produce logic control mode correspondingly.

LED driving chip with single-line pulse control mode provided by the present invention comprises and enabling and logic control circuit (Enable & Control Logic), reference voltage source (Voltage Reference), digital-analog convertor (DAC) and MOS current driver (MOS Driver), and whole LED drives chip to be used for powering to LED array (CH1-CHN).LED driving chip with single-line pulse control mode system block diagram as shown in Figure 1, wherein, enable to input by judgement with logic control circuit 100 logic state of enable signal EN, produce control logic and the algorithm of corresponding mode of operation, reference voltage source 120 provides stable reference data voltage for system, digital-analog convertor 140 is realized LED dimming function, and MOS current driver 130 produces enough large current drives LED, and whole LED drives chip to be used for powering to LED array 150.。

The mode of operation of whole chip system is divided into three kinds by LED driving chip with single-line pulse control mode of the present invention, it comprises: shutdown mode (Shut down mode), electric current output decline mode (Step downmode), and electric current output Holdover mode (Hold mode).These three kinds of mode of operations and duty transition diagram and control algolithm thereof are as shown in Figure 2.

First, judge whether input EN signal is logical one, if logical one, exporting LED electric current (Iout) is lowest high-current value Imax; If logical zero, and the duration exceed 300us, system enters shutdown mode.If EN is continuous single line pulse signal, subtract counting by 15 system down counters of logic control part, system enters electric current output decline mode, until the electric current I out of output is the 15th grade of output Imin, in the time of rolling counters forward N=15, come back to lowest high-current value Imax, countdown circulates.If EN signal is discrete pulse signal, and do not meet the Rule of judgment that the duration exceedes the EN=0 of 300us, system enters output current Holdover mode.Now, the output current of system remain between maximum Imax (being first order 1st) and minimum of a value Imin (i.e. the 15th grade of 15th) certain one-level on, the dimming function between having realized from Imin to Imax.

LED driving chip with single-line pulse control mode of the present invention, enabling can be according to the logic state of input enable signal EN with logic control circuit, judge and produce control logic signal, its integrated circuit figure as shown in Figure 3, mainly comprises following submodule:

1) mode detection module 310 (Detector), detects according to the state of input signal EN, judges and produce to export accordingly control model, i.e. light-modulating mode, Holdover mode, shutdown mode.Its specific implementation with reference to the accompanying drawings 2 state transition graph realizes.

2) dimming function module 320 (Dimming), adopts down counter and the thermometer coding circuit design of 15 systems and produces the dimming control signal CTRL_dimming of 15 grades.

3) m-digital translation functional module 330 (TDC) time, the signal of 10MHz that oscillator 340 (OSC) is produced carries out 256 frequency division, then judges and produce the system closedown signal CTRL_PWD after EN=0 and lasting 300us through the counter of 12 systems.

4) oscillator module 340 (OSC), i.e. clock generator, produces one and is subject to technique, and temperature, and the very little reference clock that is about 10MHz of supply voltage impact, for judging the lasting low level time of EN signal.

5) simple logic control module 350, control signal CTRL_dimming and CTRL_PWD are realized to logic, in the time there is logical zero in any one signal in them, all can turn-off gauge tap 370, be that LED output current 360 will stop output, thereby realize the function of shutdown.

Adopt state transition graph provided by the present invention and control algolithm, and the sequential of the major control port of the LED driving chip with single-line pulse control mode of control logic integrated circuit figure realization as shown in Figure 4, wherein, EN is the single line pulse control signal of outside input, PWD is the system power down off signal that chip internal produces, and Iout is the current signal of chip output LED port.By judging the different logic state of EN signal, produce corresponding control model, thereby reach, LED is carried out to light modulation, the object that electric current output keeps and shuts down.

LED driving chip with single-line pulse control mode provided by the present invention, can be according to the logic state of single line pulse input signal, realize LED light modulation, the function that output current keeps and shuts down, reduce greatly chip controls number of pins, and the number of sheet external component, reduce user's use cost, can meet the application demand of various growing consumer electronics products simultaneously.

Brief description of the drawings

Fig. 1, LED driving chip with single-line pulse control mode system block diagram.

Fig. 2, system transition status figure.

Fig. 3, logic control integrated circuit figure.

Fig. 4, the main interface sequence figure of system.

Specific embodiments

Below in conjunction with specific embodiment, the present invention is further elaborated.Embodiment is only for explaining instead of limitation of the present invention the present invention.

Embodiment 1

The present embodiment is 20mA by designing and Implementing a maximum output current, every one-level 1.25mA, and the LED of totally 15 grades of outputs drives chip, further sets forth the present invention.

Attached the present embodiment system block diagram that Figure 1 shows that, comprises and enabling and logic control circuit 100, reference voltage source 120, and MOS current driver 130, digital-analog convertor 140, whole LED drives chip to be used for powering to LED array 150.

2 system mode transition diagram with reference to the accompanying drawings, can obtain the detailed description of the invention of single line pulse control algolithm.The mode of operation of whole chip system can be divided into three kinds by the present embodiment, i.e. shutdown mode, electric current output decline mode and electric current output Holdover mode.These three kinds of mode of operations and duty transition diagram and control algolithm thereof are as shown in Figure 2.

First, judge whether input EN signal is logical one, if logical one, exporting LED electric current (Iout) is lowest high-current value 20mA; If logical zero, and the duration exceed 300us, system enters shutdown mode.If EN is continuous single line pulse signal, subtract counting by 15 system down counters of logic control part, system enters electric current output decline mode, and Iout is started to successively decrease step by step according to every grade of 1.25mA amplitude by 20mA, until the electric current I out of output is the 15th grade of output Imin.In the time of rolling counters forward N=15, come back to lowest high-current value Imax, countdown circulates.Even EN signal is discrete pulse signal, and do not meet the Rule of judgment that the duration exceedes the EN=0 of 300us, system enters output current Holdover mode, now, the output current of system remain between maximum Imax (being first order 1st) and minimum of a value Imin (i.e. the 15th grade of 15th) certain one-level on, the dimming function between having realized from Imin to Imax.

Claims

1. a LED driving chip with single-line pulse control mode, it is characterized in that, described chip comprises: enable and logic control circuit, reference voltage source, MOS current driver and digital-analog convertor, described chip is according to logic state and the pulse number of single line input pulse control signal, input the logic state of enable signal EN by judgement, produce control logic and the algorithm of corresponding mode of operation, if EN is continuous single line pulse signal, subtract counting by 15 system down counters of logic control part, system enters electric current output decline mode, realize the bright dark dimming function of LED, if EN is discrete pu1se signal, and do not meet the Rule of judgment that the duration exceedes the EN=0 of 300us, system enters output current Holdover mode, if exceed 300us, system enters shutdown mode.

2. LED driving chip with single-line pulse control mode according to claim 1, is characterized in that, the logic control of electric current output decline mode adopts down counter and the thermometer coding circuit design of 15 systems and produces the dimming control signal of 15 grades.

3. LED driving chip with single-line pulse control mode according to claim 1, it is characterized in that, the signal of the 10MHz that shutdown mode employing produces oscillator carries out 256 frequency division, judge through the counter of 12 systems again and produce the system closedown signal CTRL_PWD after EN=0 and lasting 300us, and control signal and system closedown signal are realized and logic, in the time there is logical zero in any one signal in them, all can turn-off gauge tap, be that LED output current will stop output, thereby realize the function of shutdown.