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參數(shù)資料
| 型號(hào)： | LM3570SDX |
| 廠商： | NATIONAL SEMICONDUCTOR CORP |
| 元件分類： | 顯示驅(qū)動(dòng)器 |
| 英文描述： | Low Noise White LED Driver System |
| 中文描述： | LED DISPLAY DRIVER, DSO14 |
| 封裝： | 4 X 3 MM, 0.80 MM HEIGHT, LLP-14 |
| 文件頁(yè)數(shù)： | 10/13頁(yè) |
| 文件大?。?/td> | 352K |
| 代理商： | LM3570SDX |
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Application Information
PRE-REGULATION
The very low input current ripple of the LM3570, resulting
from internal pre-regulation, adds very little noise to the input
line. The core of the LM3570 is very similar to that of a basic
3/2 switched capacitor regulator: it is composed of seven
switches and two flying capacitors (external). Regulation is
achieved by modulating the on-resistance of the three
switches connected to the input pin (one switch in phase one
and two in phase two). The regulation is done before the
voltage “gain stage”, giving rise to the term "pre-regulation".
Pre-regulation eliminates most of the input current ripple that
is a typical and undesirable characteristic of many switched
capacitor converters.
TOTAL OUTPUT CURRENT CAPABILITY
The LM3570 is capable of providing a total output current of
80mA. The 80mA can be divided through any combination of
the three dedicated current outputs and/or current drawn
from the V
output. When pulling current from the V
pin, the LM3570 will hold the output voltage at the regulated
4.35V. This pre-regulation occurs when the input voltage is
within the 3.0V to 5.5V operating range. If the input voltage is
between the 2.7V to 3.0V range, the V
voltage will be-
have in the same manner as the output of an unregulated
charge pump. During operation in this input voltage range,
the output voltage becomes directly related to the total out-
put current drawn from the part and the output resistance
(R
) of the charge pump.
Figure 1
displays how the
LM3570’s R
OUT
is modeled to solve for the V
OUT
voltage
V
OUT
= (V
IN
x 1.5) - ( (I
+I
) x R
OUT
)
≤
V
IN
<
3.0V and R
OUT
= 4
Dx OUTPUT CURRENT CAPABILITY
An external resistor, R
, is connected to the I
pin to set
the current to be mirrored in each of the three LED outputs.
The internal current mirror sets each LED output current with
a 100:1 ratio to the current through R
. The current mirror
circuitry matches the current through each LED to within
0.5%. An equation for approximating the LED current is:
R
SET
=100 x (1.25V / I
DX
)
PARALLEL Dx OUTPUTS FOR INCREASED CURRENT
CAPABILITY
Outputs D
through D
may be connected together in any
combination to drive higher currents through fewer LEDs.
For example in
Figure 2
, outputs D
and D
are connected
together to drive one LED while D
1
is connected to a seper-
ate LED.
With this configuration, two parallel current sources of equal
value provide current to one of the LEDs. R
SET
should
therefore be chosen so that the current through each output
is programmed to 50% of the desired current through the
parallel connected LED. For example, if 40mA is the desired
drive current for the parallel connected LED, R
SET
should be
selected so that the current through each of the outputs is
20mA. Other combinations of parallel outputs may be imple-
mented in similar fashions, such as in
Figure 3
.
Connecting outputs in parallel does not affect internal opera-
tion of the LM3570 and has no impact on the Electrical
20085004
FIGURE 1. LM3570 Charge Pump Model
20085007
FIGURE 2. One Parallel Connected and One Singular
Connected LED
20085006
FIGURE 3. One Parallel Connected LED
L
www.national.com
10
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相關(guān)代理商/技術(shù)參數(shù) |
參數(shù)描述 |
|---|---|
| LM3578 | 制造商:NSC 制造商全稱:National Semiconductor 功能描述:Switching Regulator |
| LM3578A | 制造商:NSC 制造商全稱:National Semiconductor 功能描述:Switching Regulator |
| LM3578AM | 功能描述:直流/直流開關(guān)轉(zhuǎn)換器 RoHS:否 制造商:STMicroelectronics 最大輸入電壓:4.5 V 開關(guān)頻率:1.5 MHz 輸出電壓:4.6 V 輸出電流:250 mA 輸出端數(shù)量:2 最大工作溫度:+ 85 C 安裝風(fēng)格:SMD/SMT |
| LM3578AM | 制造商:Texas Instruments 功能描述:SWITCHED MODE REG SMD 3578 SOIC8 |
| LM3578AM/NOPB | 功能描述:直流/直流開關(guān)轉(zhuǎn)換器 SWITCHING REGULATOR RoHS:否 制造商:STMicroelectronics 最大輸入電壓:4.5 V 開關(guān)頻率:1.5 MHz 輸出電壓:4.6 V 輸出電流:250 mA 輸出端數(shù)量:2 最大工作溫度:+ 85 C 安裝風(fēng)格:SMD/SMT |
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