參數(shù)資料
型號(hào)： LM3402HVMRX
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, TSOP-8
文件頁(yè)數(shù)： 12/24頁(yè)
文件大?。?/td> 431K
代理商： LM3402HVMRX
HIGH VOLTAGE BIAS REGULATOR
The LM3402/02HV contains an internal linear regulator with
a 7V output, connected between the VIN and the VCC pins.
The VCC pin should be bypassed to the GND pin with a 0.1
μF ceramic capacitor connected as close as possible to the
pins of the IC. VCC tracks VIN until VIN reaches 8.8V (typical)
and then regulates at 7V as VIN increases. Operation begins
when VCC crosses 5.25V.
INTERNAL MOSFET AND DRIVER
The LM3402/02HV features an internal power MOSFET as
well as a floating driver connected from the SW pin to the
BOOT pin. Both rise time and fall time are 20 ns each (typical)
and the approximate gate charge is 3 nC. The high-side rail
for the driver circuitry uses a bootstrap circuit consisting of an
internal high-voltage diode and an external 10 nF capacitor,
C
. V
charges C
through the internal diode while the power
MOSFET is off. When the MOSFET turns on, the internal
diode reverse biases. This creates a floating supply equal to
the V
voltage minus the diode drop to drive the MOSFET
when its source voltage is equal to V
IN
.
FAST SHUTDOWN FOR PWM DIMMING
The DIM pin of the LM3402/02HV is a TTL logic compatible
input for low frequency PWM dimming of the LED. A logic low
(below 0.8V) at DIM will disable the internal MOSFET and
shut off the current flow to the LED array. While the DIM pin
is in a logic low state the support circuitry (driver, bandgap,
VCC) remains active in order to minimize the time needed to
turn the LED array back on when the DIM pin sees a logic
high (above 2.2V). A 75 μA (typical) pull-up current ensures
that the LM3402/02HV is on when DIM pin is open circuited,
eliminating the need for a pull-up resistor. Dimming frequen-
cy, f
, and duty cycle, D
, are limited by the LED current
rise time and fall time and the delay from activation of the DIM
pin to the response of the internal power MOSFET. In general,
f
should be at least one order of magnitude lower than the
steady state switching frequency in order to prevent aliasing.
PEAK CURRENT LIMIT
The current limit comparator of the LM3402/02HV will engage
whenever the power MOSFET current (equal to the inductor
current while the MOSFET is on) exceeds 735 mA (typical).
The power MOSFET is disabled for a cool-down time that is
10x the steady-state on-time. At the conclusion of this cool-
down time the system re-starts. If the current limit condition
persists the cycle of cool-down time and restarting will con-
tinue, creating a low-power hiccup mode, minimizing thermal
stress on the LM3402/02HV and the external circuit compo-
nents.
OVER-VOLTAGE/OVER-CURRENT COMPARATOR
The CS pin includes an output over-voltage/over-current
comparator that will disable the power MOSFET whenever
V
exceeds 300 mV. This threshold provides a hard limit
for the output current. Output current overshoot is limited to
300 mV / R
SNS
by this comparator during transients.
The OVP/OCP comparator can also be used to prevent the
output voltage from rising to V
in the event of an output
open-circuit. This is the most common failure mode for LEDs,
due to breaking of the bond wires. In a current regulator an
output open circuit causes V
to fall to zero, commanding
maximum duty cycle. Figure 2 shows a method using a zener
diode, Z1, and zener limiting resistor, R
, to limit output volt-
age to the reverse breakdown voltage of Z1 plus 200 mV. The
zener diode reverse breakdown voltage, V
, must be greater
than the maximum combined V
of all LEDs in the array. The
maximum recommended value for R
Z
is 1 k
.
As discussed in the Maximum Output Voltage section, there
is a limit to how high V
can rise during an output open-circuit
that is always less than V
. If no output capacitor is used, the
output stage of the LM3402/02HV is capable of withstanding
V
indefinitely, however the voltage at the output end of
the inductor will oscillate and can go above V
IN
or below 0V.
A small (typically 10 nF) capacitor across the LED array
dampens this oscillation. For circuits that use an output ca-
pacitor, the system can still withstand V
indefinitely as
long as C
is rated to handle V
. The high current paths are
blocked in output open-circuit and the risk of thermal stress is
minimal, hence the user may opt to allow the output voltage
to rise in the case of an open-circuit LED failure.
20192112
FIGURE 2. Output Open Circuit Protection
www.national.com
12
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相關(guān)代理商/技術(shù)參數(shù)
參數(shù)描述
LM3402HVMRX/NOPB 功能描述:開(kāi)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(kāi)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
LM3402MM 功能描述:開(kāi)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(kāi)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
LM3402MM/HALF 制造商:Texas Instruments 功能描述:DRIVER LED 0.5A POWERWISE MSOP8
LM3402MM/NOPB 功能描述:開(kāi)關(guān)變換器、穩(wěn)壓器與控制器 0.5A CONSTANT CRNT BUCK REG 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(kāi)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
LM3402MMX 功能描述:開(kāi)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(kāi)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
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