参数资料
| 型号： | MAX6955ATL+T |
| 厂商： | Maxim Integrated |
| 文件页数： | 20/43页 |
| 文件大小： | 0K |
| 描述： | IC DRVR DSPL LED 40-TQFN |
| 产品培训模块： | Lead (SnPb) Finish for COTS Obsolescence Mitigation Program |
| 标准包装： | 2,500 |
| 显示器类型： | LED |
| 配置： | 7、14、16 段 |
| 接口： | I²C |
| 电流 - 电源： | 22mA |
| 电源电压： | 2.7 V ~ 5.5 V |
| 工作温度： | -40°C ~ 125°C |
| 安装类型： | 表面贴装 |
| 封装/外壳： | 40-WFQFN 裸露焊盘 |
| 供应商设备封装： | 40-TQFN-EP（6x6） |
| 包装： | 带卷 (TR) |
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MAX6955
2-Wire Interfaced, 2.7V to 5.5V LED Display
Driver with I/O Expander and Key Scan
Choosing Supply Voltage to Minimize
Power Dissipation
The MAX6955 drives a peak current of 40mA into LEDs
with a 2.2V forward-voltage drop when operated from a
supply voltage of at least 3.0V. The minimum voltage
drop across the internal LED drivers is therefore (3.0V -
2.2V) = 0.8V. If a higher supply voltage is used, the dri-
ver absorbs a higher voltage, and the driver’s power
dissipation increases accordingly. However, if the LEDs
used have a higher forward-voltage drop than 2.2V, the
supply voltage must be raised accordingly to ensure
that the driver always has at least 0.6V of headroom.
The voltage drop across the drivers with a nominal 5V
supply (5.0V - 2.2V) = 2.8V is nearly 3 times the drop
across the drivers with a nominal 3.3V supply (3.3V -
2.2V) = 1.1V. In most systems, consumption is an
important design criterion, and the MAX6955 should be
operated from the system’s 3.3V nominal supply. In
other designs, the lowest supply voltage may be 5V.
The issue now is to ensure the dissipation limit for the
MAX6955 is not exceeded. This can be achieved by
inserting a series resistor in the supply to the MAX6955,
ensuring that the supply decoupling capacitors are still
on the MAX6955 side of the resistor. For example, con-
sider the requirement that the minimum supply voltage
to a MAX6955 must be 3.0V, and the input supply
range is 5V ±5%. Maximum supply current is 35mA +
(40mA x 17) = 715mA. Minimum input supply voltage is
4.75V. Maximum series resistor value is (4.75V -
3.0V)/0.715A = 2.44 ? . We choose 2.2 ? ±5%. Worst-
case resistor dissipation is at maximum toleranced
resistance, i.e., (0.715A) 2 x (2.2 ? x 1.05) = 1.18W. The
maximum MAX6955 supply voltage is at maximum
input supply voltage and minimum toleranced resis-
tance, i.e., 5.25V - (0.715A x 2.2 ? x 0.95) = 3.76V.
Low-Voltage Operation
The MAX6955 works over the 2.7V to 5.5V supply
range. The minimum useful supply voltage is deter-
mined by the forward-voltage drop of the LEDs at the
peak current I SEG , plus the 0.8V headroom required by
the driver output stages. The MAX6955 correctly regu-
lates I SEG with a supply voltage above this minimum
voltage. If the supply drops below this minimum volt-
20
age, the driver output stages can brown out, and be
unable to regulate the current correctly. As the supply
voltage drops further, the LED segment drive current
becomes effectively limited by the output driver's on-
resistance, and the LED drive current drops. The char-
acteristics of each individual LED in a display digit are
well matched, so the result is that the display intensity
dims uniformly as supply voltage drops out of regula-
tion and beyond.
Computing Power Dissipation
The upper limit for power dissipation (P D ) for the
MAX6955 is determined from the following equation:
P D = (V+ x 35mA) + (V+ - V LED ) (DUTY x I SEG x N)
where:
V+ = supply voltage
DUTY = duty cycle set by intensity register
N = number of segments driven (worst case is 17)
V LED = LED forward voltage at I SEG
I SEG = segment current set by R SET
P D = Power dissipation, in mW if currents are in mA
Dissipation example:
I SEG = 30mA, N = 17, DUTY = 15/16,
V LED = 2.4V at 30mA, V+ = 3.6V
P D = 3.6V (35mA) + (3.6V - 2.4V)(15/16 x
30mA x 17) = 0.700W
Thus, for a 36-pin SSOP package (T JA = 1/0.0118 =
+85°C/W from Operating 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 + (0.700 x +85°C/W)
So T A = +90.5°C. Thus, the part can be operated safely
at a maximum package temperature of +85°C.
Power Supplies
The MAX6955 operates from a single 2.7V to 5.5V
power supply. Bypass the power supply to GND with a
0.1μF capacitor as close to the device as possible. Add
a 47μF capacitor if the MAX6955 is not close to the
board’s input bulk decoupling capacitor.
Maxim Integrated
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| MAX6955EVKIT | 功能描述:LED 照明开发工具 Evaluation Kit for the MAX6955 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: |
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| MAX6956AAI+ | 功能描述:LED显示驱动器 2.5-5.5V 20/28Port LED Display Driver 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 |
| MAX6956AAI+T | 功能描述:LED显示驱动器 2.5-5.5V 20/28Port LED Display Driver 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 |
| MAX6956AAI-T | 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 |
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