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參數(shù)資料
| 型號(hào)： | ISL97631 |
| 廠商： | Intersil Corporation |
| 英文描述： | White LED Boost Regulator With Integrated Schottky Diode |
| 中文描述： | 白光LED升壓調(diào)節(jié)器集成了肖特基二極管 |
| 文件頁數(shù)： | 5/8頁 |
| 文件大?。?/td> | 332K |
| 代理商： | ISL97631 |
5
FN7370.1
December 21, 2005
The magnitude of the PWM signal should be higher than the
minimum ENAB voltage high. The bench PWM dimming test
results are shown in Figure 8. In the test, two PWM
frequencies 400Hz and 1kHz are chosen to compare the
linear dimming range. It is clear that there is a wider linear
dimming range for the lower PWM frequency than for the
higher one, due to the self discharge of the output capacitor
through the LEDs during the low ENAB periods. To achieve
a better linearity with high frequencies an NMOS FET can be
placed between the FB pin and the LED stack, with its gate
driven by the same signal as ENAB. This acts to prevent self
discharge of the output capacitor during the off periods. In
the PWM dimming test, the output capacitor is 0.22μF.
ANALOG DIMMING
The second dimming method applies a variable DC voltage
(V
Dim
) at FB pin (see Figure 9) to adjust the LED current. As
the DC dimming signal voltage increases above V
FB
, the
voltages drop on R
1
and R
2
increase and the voltage drop
on R
SET
decreases. Thus, the LED current decreases.
The DC dimming signal voltage can be a variable DC voltage
or a DC voltage generated by filtering a high frequency PWM
control signal.
As brightness is directly proportional to LED currents, V
Dim
may be calculated for any desired “relative brightness” (F)
using Equation 4.
R
2
R
1
2
Where F = I
LED
(dimmed)/I
LED
(undimmed).
These equations are valid for values of R1 and R2 such that
both R1>>RSET and R2>>RSET.
The analog dimming circuit can be tailored to a desired
relative brightness for different V
Dim
ranges using
Equation 5.
Where V
Dim_max
is the maximum V
Dim
voltage and F
min
is
the minimum relative brightness (i.e., the brightness with
V
Dim_max
applied).
i.e., V
Dim_max
= 5V, F
min
= 10% (i.e., 0.1), R
2
= 189k
i.e., V
Dim_max
= 1V, F
min
= 10% (i.e., 0.1), R
2
= 35k
Open-Voltage Protection
In some applications, it is possible that the output is
opened, e.g. when the LEDs are disconnected from the
circuit or the LEDs fail. In this case the feedback voltage
will be zero. The ISL97631 will then switch to a high duty
cycle resulting in a high output voltage, which may cause
the LX pin voltage to exceed its maximum 27V rating. To
implement overvoltage protection, a zener diode Dz and a
resistor R
1
can be used at the output and FB pin to limit the
voltage on the LX pin as shown in Figure 10. It is clear that
as the zener is turned on, due to the overvoltage, the zener
diode’s current will set up a voltage on R
1
and R
SET
and this
voltage is applied on FB pin as the feedback node. This
feedback will prevent the output from reaching the
overvoltage condition. In the overvoltage protection circuit
design, the zener voltage should be larger than the
maximum forward voltage of the LED string.
FIGURE 8. PWM DIMMING LINEAR RANGE (FOR 400Hz AND
1kHz PWM FREQUENCIES CONDITION,
C
OUT
= 0.22μF)
0
2
4
6
8
10
12
14
16
18
20
0
20
40
60
80
100
DUTY-CYCLE (%)
I
O
400Hz
1kHz
I
LED
V
-------------------------------------------------------------------------
R
R
+
(
)
V
R
1
–
2
SET
=
(EQ. 3)
V
Dim
------
V
FB
1
R
1
------
F
–
+
=
(EQ. 4)
FIGURE 9. ANALOG DIMMING CONTROL APPLICATION
CIRCUIT
ISL97631
C1
1μF
V
IN
LX
ENAB
FB
GND
L1
22μH
C2
0.22μF
R
SET
4.75
OFF/ON
LEDs
V
IN
2.7V~5.5V
R1
R2
V
Dim
V
OUT
3.3k
R
2
V
V
FB
F
min
–
)
R
1
]
)
----------------------------------–
]
1
=
(EQ. 5)
ISL97631
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| ISL97631IHTZ-T7 | White LED Boost Regulator With Integrated Schottky Diode |
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相關(guān)代理商/技術(shù)參數(shù) |
參數(shù)描述 |
|---|---|
| ISL97631HTZ-T7A | 制造商:Intersil Corporation 功能描述: |
| ISL97631IHTZ | 制造商:Intersil 功能描述:6 LEDs Driver with Integrated Schottky Diode with OVP |
| ISL97631IHTZ-T7 | 功能描述:IC LED DRIVR WHITE BCKLGT TSOT-6 RoHS:是 類別:集成電路 (IC) >> PMIC - LED 驅(qū)動(dòng)器 系列:- 標(biāo)準(zhǔn)包裝:60 系列:- 恒定電流:- 恒定電壓:- 拓?fù)?線性（LDO），PWM，升壓（升壓） 輸出數(shù):8 內(nèi)部驅(qū)動(dòng)器:是 類型 - 主要:背光 類型 - 次要:RGB，白色 LED 頻率:500kHz ~ 1.5MHz 電源電壓:4.75 V ~ 26 V 輸出電壓:45V 安裝類型:* 封裝/外殼:* 供應(yīng)商設(shè)備封裝:* 包裝:* 工作溫度:-40°C ~ 85°C |
| ISL97631IHTZ-T7A | 功能描述:LED顯示驅(qū)動(dòng)器 ISL97631IHTZ HI PWR WHT LED BOOSTLT1933 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 |
| ISL97632IRT14Z | 制造商:Intersil 功能描述:LED Driver with 1-Wire Dimming(3 LED) |
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