- 您現(xiàn)在的位置：買賣IC網(wǎng) > PDF目錄385480 > LM3402HVMMX (NATIONAL SEMICONDUCTOR CORP) 0.5A Constant Current Buck Regulator for Driving High Power LEDs PDF資料下載
參數(shù)資料
| 型號： | LM3402HVMMX |
| 廠商： | NATIONAL SEMICONDUCTOR CORP |
| 元件分類： | 穩(wěn)壓器 |
| 英文描述： | 0.5A Constant Current Buck Regulator for Driving High Power LEDs |
| 中文描述： | 0.94 A SWITCHING REGULATOR, PDSO8 |
| 封裝： | PLASTIC, MSOP-8 |
| 文件頁數(shù)： | 13/22頁 |
| 文件大?。?/td> | 840K |
| 代理商： | LM3402HVMMX |
Design Considerations
SWITCHING FREQUENCY
Switching frequency is selected based on the tradeoffs be-
tween efficiency (better at low frequency), solution size/cost
(smaller at high frequency), and the range of output voltage
that can be regulated (wider at lower frequency.) Many ap-
plications place limits on switching frequency due to EMI
sensitivity. The on-time of the LM3402/02HV can be pro-
grammed for switching frequencies ranging from the 10’s of
kHz to over 1 MHz. The maximum switching frequency is
limited only by the minimum on-time requirement.
LED RIPPLE CURRENT
Selection of the ripple current,
i
F
, through the LED array is
analogous to the selection of output ripple voltage in a
standard voltage regulator. Where the output ripple in a
voltage regulator is commonly
±
1% to
±
5% of the DC output
voltage, LED manufacturers generally recommend values
for
i
F
ranging from
±
5% to
±
20% of I
F
. Higher LED ripple
current allows the use of smaller inductors, smaller output
capacitors, or no output capacitors at all. The advantages of
higher ripple current are reduction in the solution size and
cost. Lower ripple current requires more output inductance,
higher switching frequency, or additional output capacitance.
The advantages of lower ripple current are a reduction in
heating in the LED itself and greater range of the average
LED current before the current limit of the LED or the driving
circuitry is reached.
BUCK CONVERTERS WITHOUT OUTPUT CAPACITORS
The buck converter is unique among non-isolated topologies
because of the direct connection of the inductor to the load
during the entire switching cycle. By definition an inductor
will control the rate of change of current that flows through it,
and this control over current ripple forms the basis for com-
ponent selection in both voltage regulators and current regu-
lators. A current regulator such as the LED driver for which
the LM3402/02HV was designed focuses on the control of
the current through the load, not the voltage across it. A
constant current regulator is free of load current transients,
and has no need of output capacitance to supply the load
and maintain output voltage. Referring to the Typical Appli-
cation circuit on the front page of this datasheet, the inductor
and LED can form a single series chain, sharing the same
current. When no output capacitor is used, the same equa-
tions that govern inductor ripple current,
i
L
, also apply to the
LED ripple current,
i
F
. For a controlled on-time converter
such as LM3402/02HV the ripple current is described by the
following expression:
A minimum ripple voltage of 25 mV is recommended at the
CS pin to provide good signal-to-noise ratio (SNR). The CS
pin ripple voltage,
V
SNS
, is described by the following:
V
SNS
=
i
F
x R
SNS
BUCK CONVERTERS WITH OUTPUT CAPACITORS
A capacitor placed in parallel with the LED or array of LEDs
can be used to reduce the LED current ripple while keeping
the same average current through both the inductor and the
LED array. This technique is demonstrated in Design Ex-
ample 1. With this topology the output inductance can be
lowered, making the magnetics smaller and less expensive.
Alternatively, the circuit could be run at lower frequency but
keep the same inductor value, improving the efficiency and
expanding the range of output voltage that can be regulated.
Both the peak current limit and the OVP/OCP comparator
still monitor peak inductor current, placing a limit on how
large
i
can be even if
i
is made very small. A parallel
output capacitor is also useful in applications where the
inductor or input voltage tolerance is poor. Adding a capaci-
tor that reduces
i
to well below the target provides head-
room for changes in inductance or V
that might otherwise
push the peak LED ripple current too high.
Figure 4 shows the equivalent impedances presented to the
inductor current ripple when an output capacitor, C
, and its
equivalent series resistance (ESR) are placed in parallel with
the LED array. The entire inductor ripple current flows
through R
SNS
to provide the required 25 mV of ripple voltage
for proper operation of the CS comparator.
To calculate the respective ripple currents the LED array is
represented as a dynamic resistance, r
. LED dynamic re-
sistance is not always specified on the manufacturer’s
datasheet, but it can be calculated as the inverse slope of
the LED’s V
vs. I
curve. Note that dividing V
by I
will give
an incorrect value that is 5x to 10x too high. Total dynamic
resistance for a string of n LEDs connected in series can be
calculated as the r
of one device multiplied by n. Inductor
ripple current is still calculated with the expression from Buck
Regulators without Output Capacitors. The following equa-
tions can then be used to estimate
i
F
when using a parallel
capacitor:
The calculation for Z
assumes that the shape of the induc-
tor ripple current is approximately sinusoidal.
Small values of C
that do not significantly reduce
i
can
also be used to control EMI generated by the switching
action of the LM3402/02HV. EMI reduction becomes more
important as the length of the connections between the LED
and the rest of the circuit increase.
20192115
FIGURE 4. LED and C
O
Ripple Current
L
www.national.com
13
相關(guān)PDF資料 |
PDF描述 |
|---|---|
| LM3402MM | 0.5A Constant Current Buck Regulator for Driving High Power LEDs |
| LM3402MMX | 0.5A Constant Current Buck Regulator for Driving High Power LEDs |
| LM3404 | 1.0A Constant Current Buck Regulator for Driving High Power LEDs |
| LM3404HV | 1.0A Constant Current Buck Regulator for Driving High Power LEDs |
| LM3405 | 550kHz/1.6MHz 1A Constant Current Buck Regulator for Powering LEDs |
相關(guān)代理商/技術(shù)參數(shù) |
參數(shù)描述 |
|---|---|
| LM3402HVMMX/NOPB | 功能描述:開關(guān)變換器、穩(wěn)壓器與控制器 RoHS:否 制造商:Texas Instruments 輸出電壓:1.2 V to 10 V 輸出電流:300 mA 輸出功率: 輸入電壓:3 V to 17 V 開關(guān)頻率:1 MHz 工作溫度范圍: 安裝風(fēng)格:SMD/SMT 封裝 / 箱體:WSON-8 封裝:Reel |
| LM3402HVMR | 制造商:Texas Instruments 功能描述:Conv DC-DC Single Step Down 6V to 75V 8-Pin PSOP EP Rail 制造商:Texas Instruments 功能描述:Buck Reg for Hi Pwr LED Drvs, LM3402HVMR |
| LM3402HVMR/NOPB | 功能描述:開關(guān)變換器、穩(wěn)壓器與控制器 RoHS:否 制造商:Texas Instruments 輸出電壓:1.2 V to 10 V 輸出電流:300 mA 輸出功率: 輸入電壓:3 V to 17 V 開關(guān)頻率:1 MHz 工作溫度范圍: 安裝風(fēng)格:SMD/SMT 封裝 / 箱體:WSON-8 封裝:Reel |
| LM3402HVMRX | 制造商:NSC 制造商全稱:National Semiconductor 功能描述:0.5A Constant Current Buck Regulator for Driving High Power LEDs |
| LM3402HVMRX/NOPB | 功能描述:開關(guān)變換器、穩(wěn)壓器與控制器 RoHS:否 制造商:Texas Instruments 輸出電壓:1.2 V to 10 V 輸出電流:300 mA 輸出功率: 輸入電壓:3 V to 17 V 開關(guān)頻率:1 MHz 工作溫度范圍: 安裝風(fēng)格:SMD/SMT 封裝 / 箱體:WSON-8 封裝:Reel |
發(fā)布緊急采購，3分鐘左右您將得到回復(fù)。