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參數(shù)資料
| 型號(hào)： | SP7648TR |
| 英文描述： | Low Reference High Efficiency Boost Regulator |
| 中文描述： | 高效率低參考升壓穩(wěn)壓器 |
| 文件頁數(shù)： | 8/12頁 |
| 文件大小： | 236K |
| 代理商： | SP7648TR |
8
Date: 7/20/05
SP7648 Ultra-low Quiescent Current, High Efficiency Boost Regulator Copyright 2005 Sipex Corporation
current t
o a
voi
d saturating the inductor,
which would result in a loss in efficiency and
could damage the inductor. The SP7648
evaluation board uses a R
LIM
value of 1K
for an I
PEAK
= 1.6A to allow the circuit to
deliver up to 700mA for V
IN
= 3.3V and V
OUT
= 4.2V. Other values could be selected using
the above relationships.
_________________USING THE FLASH
CONTROL PIN
The SP7648 will regulate the output by the
equations above depending on the state of
the FLASH pin. When the FLASH pin is low
(<0.4V), the internal reference voltage is
defined as 0.8V. When the FLASH pin is
high (>0.4V), the internal reference voltage
is defined as 0.288V. This allows the use of
smaller values for the sense resistor for
current regulation mode. This improves effi-
ciency and reduces the physical size of the
sense resistor. An external MOSFET switch
can be used to change the sense resistor
when changing to the Flash Mode.
________________ HIGH BRIGHTNESS
WHITE LED
For the high brightness LumiLED white LED
application, the SP7648 is generally pro-
grammed as a current source. The bias
resistors R1 and R2 are used to set the
operating current of the white LED with the
equation:
R = V
FB
/I
F
where V
FB
is 0.8V in torch mode and 0.288V
in flash mode, I
F
is the operating current of
THEORY OF OPERATION
the LED. To set the operating current to be
about 200mA in torch mode, the flash pin is
forced low, R2 is selected as 0.8V/ 0.2 = 4
,
as shown in the typical application circuit. To
set the operating current to 700mA in flash
mode, the flash pin is forced high, R is
selected as 0.288V/0.41
= 700mA. In real-
ity R in Flash includes the series MOSFET
R
DSON
and the parallel combination of R
2
=
4
shown by the formula:
R in Flash = {R
1
X (R
2
+ Q
1
R
DSON
)}
{R
1
+ R
2
+ Q
1
R
DSON
}
If the SP7648 is powered up before the LED
is plugged in, the circuit will bring the feed-
back pin to ZeroV and the SP7648 has a
feature to set the output voltage to be 5V.
Once the LED is plugged in, the feedback
pin will go up to 0.8V in torch mode or 0.288V
in flash mode and begin to regulate. The
output voltage will go from 5V to V
F
+V
FB
,
where V
F
is the forward voltage of the LED.
When the LED is open, the feedback pin
voltage will go to ZeroV and the output
voltage will go to 5V which will protect the
part from overvoltage at the output.
One approach to control LED brightness is
to apply a PWM signal to the SHDN input of
the SP7648. In this case, the output current
will be equal to the product of V
REF
/R1 and
the average duty cycle at the SHDN pin. An
optional 10K
potentiometer may also be
used for dimming the LED current by varying
the potentiometer between low brightness
and full brightness.
If the FB pin is pulled below 150mV the
output will default to 5V defined by an inter-
nal resistor divider.
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相關(guān)代理商/技術(shù)參數(shù) |
參數(shù)描述 |
|---|---|
| SP7648UEB | 制造商:SIPEX 制造商全稱:Sipex Corporation 功能描述:Evaluation Board Manual |
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| SP7650_06 | 制造商:SIPEX 制造商全稱:Sipex Corporation 功能描述:Wide Input Voltage Range 3A, 300kHz, Buck Regulator |
| SP7650EB | 功能描述:電源管理IC開發(fā)工具 Eval Board for SP7650 Series RoHS:否 制造商:Maxim Integrated 產(chǎn)品:Evaluation Kits 類型:Battery Management 工具用于評(píng)估:MAX17710GB 輸入電壓: 輸出電壓:1.8 V |
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