參數(shù)資料
型號： MAX6978
廠商： Maxim Integrated Products, Inc.
元件分類： LED驅(qū)動器
英文描述： 8-Port, 5.5V Constant-Current LED Driver with LED Fault Detection and Watchdog
中文描述： 8端口、5.5V恒流LED驅(qū)動器，帶有LED故障檢測和看門狗
文件頁數(shù)： 9/13頁
文件大?。?/td> 327K
代理商： MAX6978
tain the same data (validating the status), and second
whether faults are reported by the actual logic level.
The fault status bit identifies which driver chip has at
least one open-circuit LED. It is possible to determine
how many LEDs driven by a chip are at fault by running
eight test patterns, each of which lights a different sin-
gle LED. The fault status bit then effectively identifies
only one output at a time.
Applications Information
Selecting External Component R
SET
to Set
LED Output Current
The MAX6978 uses an external resistor R
SET
to set the
LED current for outputs OUT0–OUT7. The minimum
allowed value of R
SET
is 307.6
, which sets the output
currents to 55mA. The maximum allowed value of R
SET
is 1.5k
. The reference value, 360
, 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
MAX6978 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
N = number of MAX6978 outputs driving LEDs at the
same time (maximum is 8)
V
OUT
= MAX6978 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
Dissipation example:
I
OUT
= 47mA, N = 8, DUTY = 1, V
OUT
= 2V, V+ = 5.25V
P
D
= (5.25V x 25mA) + (2V x 1 x 47mA x 8) = 0.883W
Thus, for a 16-pin TSSOP package (T
JA
= 1 / 0.0213 =
+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
+
(0.883 x 46.95°C/W)
so T
A
= +108.5°C.
Overtemperature Cutoff
The MAX6978 contains an internal temperature sensor
that turns off all outputs when the die temperature
exceeds approximately +165°C. The outputs are
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 will be the load LEDs cycling between on
and off as the driver repeatedly overheats and cools,
alternately turning the LEDs off and then back on again.
Power-Supply Considerations
The MAX6978 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 MAX6978 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 4 to 16 MAX6978s. The
necessary capacitance depends on the LED load cur-
rent, PWM switching frequency, and serial interface
speed. Inadequate V+ decoupling can cause timing
problems, and very noisy LED supplies can affect LED
current regulation.
For the TSSOP version, connect the underside exposed
pad to GND.
Chip Information
TRANSISTOR COUNT: 2382
PROCESS: BiCMOS
M
8-Port, 5.5V Constant-Current LED Driver with
LED Fault Detection and Watchdog
_______________________________________________________________________________________
9
LE
OUT_
LE
OUT_
CLK
OUT_
CLK
OUT_
t
CRR
t
CRF
t
LRR
t
LRF
Figure 3. LE and CLK to OUT_ Timing
相關(guān)PDF資料
PDF描述
MAX6978AUE 8-Port, 5.5V Constant-Current LED Driver with LED Fault Detection and Watchdog
MAX6978APE 8-Port, 5.5V Constant-Current LED Driver with LED Fault Detection and Watchdog
MAX6978AEE 8-Port, 5.5V Constant-Current LED Driver with LED Fault Detection and Watchdog
MAX6979 AND-OR-invert Gates 14-CDIP -55 to 125
MAX6980 4-Wide AND-OR-invert Gates 14-CFP -55 to 125
相關(guān)代理商/技術(shù)參數(shù)
參數(shù)描述
MAX6978AAE 功能描述:LED顯示驅(qū)動器 RoHS:否 制造商:Micrel 數(shù)位數(shù)量:5 片段數(shù)量: 安裝風(fēng)格:SMD/SMT 封裝 / 箱體:PLCC-44 工作電源電壓:4.75 V to 11 V 最大電源電流:10 mA 最大工作溫度:+ 85 C 最小工作溫度:- 40 C 封裝:Tube
MAX6978AAE-T 功能描述:LED顯示驅(qū)動器 RoHS:否 制造商:Micrel 數(shù)位數(shù)量:5 片段數(shù)量: 安裝風(fēng)格:SMD/SMT 封裝 / 箱體:PLCC-44 工作電源電壓:4.75 V to 11 V 最大電源電流:10 mA 最大工作溫度:+ 85 C 最小工作溫度:- 40 C 封裝:Tube
MAX6978AEE 制造商:Maxim Integrated Products 功能描述:8-PORT, 5.5V CONSTANT-CURRENT LED DRIVER WITH - Rail/Tube
MAX6978APE 功能描述:LED照明驅(qū)動器 8-Port 5.5V Constant Current LED Driver RoHS:否 制造商:STMicroelectronics 輸入電壓:11.5 V to 23 V 工作頻率: 最大電源電流:1.7 mA 輸出電流: 最大工作溫度: 安裝風(fēng)格:SMD/SMT 封裝 / 箱體:SO-16N
MAX6978APE+ 功能描述:LED顯示驅(qū)動器 Integrated Circuits (ICs) RoHS:否 制造商:Micrel 數(shù)位數(shù)量:5 片段數(shù)量: 安裝風(fēng)格:SMD/SMT 封裝 / 箱體:PLCC-44 工作電源電壓:4.75 V to 11 V 最大電源電流:10 mA 最大工作溫度:+ 85 C 最小工作溫度:- 40 C 封裝:Tube
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