Freescale MC34844 10路LED电视背光驱动解决方案

电子工程师 2019-02-24 1067

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关键词： Freescale , LED电视 , MC34844 , 背光驱动

Freescale公司的 MC34844/A 是集成了电源的10路LED背光驱动器，工作电压7.0-28V，能驱动160个10路并联的LED串。每串的电流匹配在±2%内，可通过I2C/SM总线接口进行编程。LED亮度调光256级，可编程到65,000:1 (256:1 PWM, 256:1 电流 DAC)，集成的DC/DC转换器效率为90%，MC34844每路LED电流多达50mA，MC34844A每路LED电流多达80mA，主要用在宽达43吋HDTV，笔记本电脑，GPS屏等。本文介绍了MC34844/A主要特性，方框图，多种应用电路以及KIT34844AEPEVBE评估板主要特性，电路图和材料清单。

10 Channel LED Backlight Driver with Integrated Power Supply

The 34844/A is a high efficiency, LED driver for use in backlighting LCD displays from 10" to 20"+. Operating from supplies of 7.0 to 28 V, the MC34844/A is capable of driving up to 160 LEDs in 10 parallel strings. Current in the 10 strings is matched to within ±2%, and can be programmed via the I2C/SM Bus interface.

The 34844/A also includes a Pulse Width Monitor (PWM) generator for LED dimming. The LEDs can be dimmed to one of 256 levels, programmed through the I2C/SM Bus interface. Up to 65,000:1 (256:1 PWM, 256:1 Current DAC) dimming ratio.

The integrated boost converter generates the minimum output voltage required to keep all LEDs illuminated with the selected current, providing the highest efficiency possible.

The 34844 has an integrated boost self-clocks at a default frequency of 600 kHz, but may be programmed via I2C to 150/300/600/1200 kHz. The PWM frequency can be set from 100 Hz to 25 kHz, or can be synchronized to an external input. If not synchronized to another source, the internal PWM rate outputs on the CK pin. This enables multiple devices to be synchronized together.

The 34844A has a default boost frequency of 320 kHz, but may be programmed via I2C to 160/320/650/1300 kHz. The PWM frequency can be set from 110 Hz to 27 kHz, or can be synchronized to an external input. If not synchronized to another source, the internal PWM rate outputs on the CK pin. This enables multiple devices to be synchronized together.

The 34844/A also supports optical/temperature closed loop operation and also features LED over-temperature protection, LED short protection, and LED open circuit protection. The IC also includes over-voltage protection, over-current protection, and under-voltage lockout.

MC34844主要特性：

•Input voltage of 7.0 to 28 V

•2.5 A integrated boost FET

•Up to 50 mA on the 34844 LED current per channel

•Up to 80 mA on the 34844A LED current per channel

•90% efficiency (DC: DC)

•I2C/SM Bus interface

•10 channel current mirror with ±2% current matching

•Boost output voltage up to 60V, with Dynamic Headroom Control (DHC)

•pWM frequency programmable or synchronizable from 100 to 25,000 Hz for the 34844

•pWM frequency programmable or synchronizable from 110 to 27,000 Hz for the 34844A

•32-Ld 5x5x1.0mm TQFN Package

MC34844应用：

•Monitors and HDTV - up to 42 inch

•personal Computer Notebooks

•GPS Screens

•Small screen Televisions

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图1。MC34844简化方框图

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图2。MC34844简化应用框图（SM总线模式）

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图3。MC34844A简化应用框图（人工模式）

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图4。MC34844人工模式应用电路图（单线控制）

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图5。MC34844人工模式应用电路图（两线控制）

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图6。MC34844 SM总线模式应用电路图

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图7。MC34844 SM主-从连接电路图

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图8。MC34844A高输出应用电路（人工模式）：条件：VIN = 60-72V, VOUT = 120 V, 负载= 40S8P, ILED = 60 mA, OVP = 125 V, fSW = 300

KIT34844AEPEVBE评估板

The KIT34844AEPEVBE Evaluation board supports the 34844/A, which is a high efficiency, LED driver for use in backlighting LCD displays from 10" to 20"+. Operating from supplies of 7.0 to 28V, the MC34844/A is capable of driving up to 160 LEDs in 10 parallel strings. Current in the 10 strings is matched to within ±2%, and can be programmed via the I2C/SM Bus interface.

The 34844/A also includes a Pulse Width Monitor (PWM) generator for LED dimming. The LEDs can be dimmed to one of 256 levels, programmed through the I2C/SM Bus interface. Up to 65,000:1 (256:1 PWM, 256:1 Current DAC) dimming ratio.

The integrated boost converter generates the minimum output voltage required to keep all LEDs illuminated with the selected current, providing the highest efficiency possible.

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图9。KIT34844AEPEVBE评估板外形图

KIT34844AEPEVBE评估板主要特性：

Input voltage of 7.0 to 28V

2.5A integrated boost FET

Up to 50 mA on the 34844 LED current per channel

Up to 80 mA on the 34844A LED current per channel

90% efficiency (DC: DC)

I2C/SM Bus interface

10 channel current mirror with ±2% current matching

Boost output voltage up to 60V, with Dynamic Headroom Control (DHC)

pWM frequency programmable or synchronizable from 100 to 25,000 Hz for the 34844

pWM frequency programmable or synchronizable from 110 to 27,000 Hz for the 34844A

32-Ld 5x5x1.0mm TQFN Package

KIT34844AEPEVBE评估板工作参数：

•Input Voltage (Vin) = 24V +/- 10%

•LED Load = 16 Leds x 10 Channels

•Expected Output Voltage (Vout) = around 47V

•Duty Cycle = All range.

•pWM Minimum Pulse Width = 400ns

•LED Current = 60mA

•HW OVP = 53V

•Boost Frequency = 330KHz (Typ)

•pWM Freq= 200 Hz to 25KHz (5V), or 100% Duty Cycle

•Master Mode

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图10。KIT34844AEPEVBE评估板电路图
KIT34844AEPEVBE评估板材料清单：

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