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8-Port, 36V Constant-Current LED Driver
N = number of MAX6970 outputs driving LEDs at the
same time (maximum is eight)
LE
OUT_
t LRF
V OUT = MAX6970 port output voltage when driving load
LED(s)
I OUT = LED drive current programmed by R SET
P D = power dissipation, in mW if currents are in mA.
LE
OUT_
t LRR
Dissipation example:
I OUT = 50mA, N = 8, DUTY = 1, V OUT = 2V, V+ = 5.25V
P D = (5.25V x 25mA) + (2V x 1 x 50mA x 8) = 0.931W.
Thus, for a 16-pin TSSOP package (T JA = 1 / 0.0213 =
CLK
OUT_
t CRF
+46.95°C/W from the Absolute Maximum Ratings ), the
maximum allowed ambient temperature T A is given by:
T J(MAX) = T A + (P D x T JA ) = +150°C = T A + (0.931 x
46.95°C/W)
so T A = +106.3°C.
CLK
t CRR
OUT_
Figure 3. LE and CLK to OUT_ Timing
Applications Information
Selecting External Component R SET to Set
LED Output Current
The MAX6970 uses an external resistor R SET to set the
LED current for outputs OUT0 to OUT7. The minimum
allowed value of R SET is 327.3 Ω , which sets the output
currents up to 55mA. The reference value, 360 Ω , sets
the output currents to 50mA. To set a different output
current, use the formula:
R SET = 18,000 / I OUT
where I OUT is the desired output current in mA.
Computing Power Dissipation
The upper limit for power dissipation (P D ) for the
MAX6970 is determined from the following equation:
P D = (V+ x I+) + (V OUT x DUTY x I OUT x N)
where:
V+ = supply voltage
I+ = operating supply current when sinking I OUT LED
drive current into N outputs
DUTY = PWM duty cycle applied to OE
Overtemperature Cutoff
The MAX6970 contains an internal temperature sensor
that turns off all outputs when the die temperature
exceeds approximately +165°C. The outputs are re-
enabled again when the die temperature drops below
approximately +140°C. Register contents are not
affected, so when a driver is overdissipating, the exter-
nal symptom is the load LEDs cycling between on and
off as the driver repeatedly overheats and cools, alter-
nately turning the LEDs off and then back on again.
Power-Supply Considerations
The MAX6970 operates with a chip supply V+, and one
or more LED supplies. Bypass each supply to GND
with a 0.1μF capacitor as close to the MAX6970 as pos-
sible. This is normally adequate for static LED driving.
For multiplex or PWM applications, it is necessary to
add an additional bulk electrolytic capacitor of 4.7μF or
more to each supply for every four to 16 MAX6970s.
The necessary capacitance depends on the LED load
current, PWM switching frequency, and serial-interface
speed. Inadequate V+ decoupling can cause timing
problems, and very noisy LED supplies can affect LED
current regulation.
Chip Information
PROCESS: BiCMOS
8
_______________________________________________________________________________________
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相关代理商/技术参数
MAX6970AUE+T 功能描述:LED照明驱动器 8-Port 36V Constant Current LED 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
MAX6970AUE-T 功能描述:LED照明驱动器 8-Port 36V Constant Current LED 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
MAX6970EVKIT+ 功能描述:LED 照明开发工具 Evaluation Kit for the MAX6970 RoHS:否 制造商:Fairchild Semiconductor 产品:Evaluation Kits 用于:FL7732 核心: 电源电压:120V 系列: 封装:
MAX6971ANG 功能描述:LED照明驱动器 16-Port 36V Constant Current LED 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
MAX6971ANG+ 功能描述:LED照明驱动器 16-Port 36V Constant Current LED 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
MAX6971AUG 功能描述:LED显示驱动器 RoHS:否 制造商:Micrel 数位数量:5 片段数量: 安装风格:SMD/SMT 封装 / 箱体:PLCC-44 工作电源电压:4.75 V to 11 V 最大电源电流:10 mA 最大工作温度:+ 85 C 最小工作温度:- 40 C 封装:Tube
MAX6971AUG+ 功能描述:LED照明驱动器 16-Port 36V Constant Current LED 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
MAX6971AUG+T 功能描述:LED照明驱动器 16-Port 36V Constant Current LED 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