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MC34844
FUNCTIONAL DESCRIPTION
FUNCTIONAL INTERNAL BLOCK DESCRIPTION
If I 2 C communication is not present, FAIL condition should
be reset by removing the failure and re-enabling the device
thru the EN pin.
OPTICAL AND TEMPERATURE CONTROL LOOP
The 34844 supports both optical and temperature loop
control.
For temperature loop control, the LED brightness can be
adjusted depending on the temperature of the LEDs.
For optical loop control, the 34844 supports both optical
closed loop backlight control, where the brightness of the
backlight is maintained at a required level by adjusting the
light output, until the desired level is achieved, or with
ambient light control, where the backlight brightness
increases as ambient light increases.
Both temperature and optical loops are supported through
the PIN and NIN pins. Each pin supports a 0-2.048 V input
range which affects the current through the LEDs. The PIN
Figure 6. Single Channel Disconnect Circuit.
For applications where multiple failure detection is
required, then one 100 kohm resistor must be placed from
each channel to a diode (D2) connected to VDC2. The
resistor will provide a pull up voltage to the disconnected
channels so that they do not interfere with the DHC circuit.
The diode (D2) ensures that when the connected channels
are in PWM off state the LED strings do no conduct current
to VDC2. (See Figure 7 )
pin increases current as the voltage rises from 0-2.048 V.
The NIN pin reduces current as the voltage rises from 0-
2.048 V.
A 10.2 k resistor or higher value must be used at the ISET
pin if the part is configured to use PIN+NIN control loop
functionality, the 50 mA maximum current is achieved at the
higher allowed level of PIN/NIN pins, ensuring the maximum
current of the LED Drivers are not exceeded.
The optical and temperature control loop can be disabled
by I 2 C setting bits (PINEN & NINEN), or by tying PIN and NIN
pins high (>2.2 V) it is called V SET mode, and the LED Driver
maximum current is set to 50 mA by using a 5.1 k resistor at
the ISET pin.
( VPIN × ICH [ RegisterValue ] )
RSET [ ohms ] × 2
( 2.048 – VNIN ) × ICH [ RegisterValue ]
RSET [ ohms ] × 2
( 2.048 – VNIN + VPIN ) × ICH [ RegisterValue ]
RSET [ ohms ] × 2
Current on LED Channel (PIN mode)
Current [ A ] = ----------------------------------------------------------------------------------------
Current on LED Channel (NIN mode)
Current [ A ] = -------------------------------------------------------------------------------------------------------------
Current on LED Channel (PIN+NIN mode)
Current [ A ] = -----------------------------------------------------------------------------------------------------------------------------------
LED FAILURE PROTECTION
Eqn. 3
Eqn. 4
Eqn. 5
Figure 7. Resistor/Diode placement for multiple open
circuit detection
If the fail pin cannot be cleared by software then it indicates
that the failure is because of t an over-current in the Boost.
Since this is a critical failure the only way to clear it is by
releasing the part from the over-current condition and then
shutdown the part (Refer to Table 5 )
Open LED Protection
If LED fails open in any of the LED strings, the voltage in
that channel will be pulled close to zero, which will cause the
channel to be disabled. As a result, the boost output voltage
will go to the OVP level and then come down to the regulation
level to continue powering the rest of the LED strings.
Short LED Protection
If an LED shorted in any of the LED strings, the device will
continue to operate without interruption. However, if the
34844
Analog Integrated Circuit Device Data
19
Freescale Semiconductor
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相关代理商/技术参数
MC34844EPR2
功能描述:LED照明驱动器 BACKLIGHT LED DRIVER W/10 CHANNELS RoHS:否 制造商:STMicroelectronics 输入电压:11.5 V to 23 V 工作频率: 最大电源电流:1.7 mA 输出电流: 最大工作温度: 安装风格:SMD/SMT 封装 / 箱体:SO-16N
MC34845
制造商:SPC Multicomp 功能描述:RECEPTACLE FREE 16WAY 制造商:SPC Multicomp 功能描述:RECEPTACLE, FREE, 16WAY
MC34845AEP
功能描述:LED照明驱动器 6-Ch LED Backlt Driver RoHS:否 制造商:STMicroelectronics 输入电压:11.5 V to 23 V 工作频率: 最大电源电流:1.7 mA 输出电流: 最大工作温度: 安装风格:SMD/SMT 封装 / 箱体:SO-16N
MC34845AEPR2
功能描述:LED照明驱动器 6-Ch LED Backlt Driver RoHS:否 制造商:STMicroelectronics 输入电压:11.5 V to 23 V 工作频率: 最大电源电流:1.7 mA 输出电流: 最大工作温度: 安装风格:SMD/SMT 封装 / 箱体:SO-16N
MC34845BEP
功能描述:USB 接口集成电路 6-Ch LED Backlt Driver RoHS:否 制造商:Cypress Semiconductor 产品:USB 2.0 数据速率: 接口类型:SPI 工作电源电压:3.15 V to 3.45 V 工作电源电流: 最大工作温度:+ 85 C 安装风格:SMD/SMT 封装 / 箱体:WLCSP-20
MC34845BEPR2
功能描述:USB 接口集成电路 6-Ch LED Backlt Driver RoHS:否 制造商:Cypress Semiconductor 产品:USB 2.0 数据速率: 接口类型:SPI 工作电源电压:3.15 V to 3.45 V 工作电源电流: 最大工作温度:+ 85 C 安装风格:SMD/SMT 封装 / 箱体:WLCSP-20
MC34845CEP
功能描述:LED照明驱动器 6-Ch LED Backlt Driver RoHS:否 制造商:STMicroelectronics 输入电压:11.5 V to 23 V 工作频率: 最大电源电流:1.7 mA 输出电流: 最大工作温度: 安装风格:SMD/SMT 封装 / 箱体:SO-16N
MC34845CEPR2
功能描述:LED照明驱动器 6-Ch LED Backlt Driver RoHS:否 制造商:STMicroelectronics 输入电压:11.5 V to 23 V 工作频率: 最大电源电流:1.7 mA 输出电流: 最大工作温度: 安装风格:SMD/SMT 封装 / 箱体:SO-16N