参数资料
型号: MAX6957ANI
厂商: Maxim Integrated
文件页数: 18/25页
文件大小: 0K
描述: IC DRIVER LED PORT 20/28 28-DIP
产品培训模块: Lead (SnPb) Finish for COTS
Obsolescence Mitigation Program
标准包装: 14
显示器类型: LED
配置: 7、16、20 段
接口: 4 线串行
电流 - 电源: 180µA
电源电压: 2.5 V ~ 5.5 V
工作温度: -40°C ~ 125°C
安装类型: 通孔
封装/外壳: 28-DIP(0.300",7.62mm)
供应商设备封装: 28-PDIP
包装: 管件
4-Wire-Interfaced, 2.5V to 5.5V, 20-Port and
28-Port LED Display Driver and I/O Expander
Table 11. Even Individual Segment Current Format
SEGMENT
LED DRIVE
FRACTION
CONSTANT
CURRENT WITH
ADDRESS
CODE (HEX)
D7
D6
D5
D4
D3
D2
D1
D0
HEX CODE
R ISET = 39k Ω (mA)
1/16
2/16
3/16
4/16
5/16
6/16
7/16
1.5
3
4.5
6
7.5
9
10.5
0x12 to 0x1F
0x12 to 0x1F
0x12 to 0x1F
0x12 to 0x1F
0x12 to 0x1F
0x12 to 0x1F
0x12 to 0x1F
0
0
0
0
0
0
0
0
0
0
0
1
1
1
0
0
1
1
0
0
1
0
1
0
1
0
1
0
0xX0
0xX1
0xX2
0xX3
0xX4
0xX5
0xX6
8/16
9/16
10/16
11/16
12/16
13/16
14/16
15/16
16/16
12
13.5
15
16.5
18
19.5
21
22.5
24
0x12 to 0x1F
0x12 to 0x1F
0x12 to 0x1F
0x12 to 0x1F
0x12 to 0x1F
0x12 to 0x1F
0x12 to 0x1F
0x12 to 0x1F
0x12 to 0x1F
See Table 12.
0
1
1
1
1
1
1
1
1
1
0
0
0
0
1
1
1
1
1
0
0
1
1
0
0
1
1
1
0
1
0
1
0
1
0
1
0xX7
0xX8
0xX9
0xXA
0xXB
0xXC
0xXD
0xXE
0xXF
Applications Information
Driving Bicolor and Tricolor LEDs
Bicolor digits group a red and a green die together for
each display element, so that the element can be lit
red, green (or orange), depending on which die (or
both) is lit. The MAX6957 allows each segment's cur-
rent to be set individually from 1/16th (minimum current
and LED intensity) to 16/16th (maximum current and
LED intensity), as well as off (zero current). Thus, a
bicolor (red-green) segment pair can be set to 289
color/intensity combinations. A discrete or CA tricolor
(red-green-yellow or red-green-blue) segment triad can
be set to 4913 color/intensity combinations.
Power Dissipation Issues
Each MAX6957 port can sink a current of 24mA into an
LED with a 2.4V 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 - 2.4V) = 0.6V. The MAX6957 can sink 28 x 24mA
= 672mA when all outputs are operating as LED seg-
ment drivers at full current. On a 3.3V supply, a
MAX6957 dissipates (3.3V - 2.4V) ? 672mA = 0.6W
when driving 28 of these 2.4V forward-voltage drop
LEDs at full current. This dissipation is within the ratings
of the 36-pin SSOP package with an ambient tempera-
ture up to +98°C. If a higher supply voltage is used or
the LEDs used have a lower forward-voltage drop than
2.4V, the MAX6957 absorbs a higher voltage, and the
MAX6957's power dissipation increases.
If the application requires high drive current and high
supply voltage, consider adding a series resistor to
each LED to drop excessive drive voltage off-chip. For
example, consider the requirement that the MAX6957
must drive LEDs with a 2.0V to 2.4V specified forward-
voltage drop, from an input supply range is 5V ±5%
with a maximum LED current of 20mA. Minimum input
supply voltage is 4.75V. Maximum LED series resistor
value is (4.75V - 2.4V - 0.6V)/0.020A = 87.5 Ω . We
choose 82 Ω ±2%. Worst-case resistor dissipation is at
maximum toleranced resistance, i.e., (0.020A) 2 ? (82 Ω
? 1.02) = 34mW. The maximum MAX6957 dissipation
per LED is at maximum input supply voltage, minimum
toleranced resistance, minimum toleranced LED for-
ward-voltage drop, i.e., 0.020 x (5.25V - 2.0V - (0.020A
? 82 Ω x 0.98)) = 32.86mW. Worst-case MAX6957 dissi-
pation is 920mW, driving all 28 LEDs at 20mA full cur-
rent at once, which meets the 941mW dissipation
ratings of the 36-pin SSOP package.
18
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