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参数资料
| 型号： | LM3402_07 |
| 厂商： | National Semiconductor Corporation |
| 英文描述： | 0.5A Constant Current Buck Regulator for Driving High Power LEDs |
| 中文描述： | 0.5A的恒流降压稳压器用于驱动高功率LED |
| 文件页数： | 4/24页 |
| 文件大小： | 431K |
| 代理商： | LM3402_07 |
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
F 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
B. VCC charges CB 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
CC 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 A (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
DIM, and duty cycle, DDIM, 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
DIM 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
SNS 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
O(MAX) 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
SNS to fall to zero, commanding
maximum duty cycle. Figure 2 shows a method using a zener
diode, Z1, and zener limiting resistor, R
Z, to limit output volt-
age to the reverse breakdown voltage of Z1 plus 200 mV. The
zener diode reverse breakdown voltage, V
Z, must be greater
than the maximum combined V
F 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
O can rise during an output open-circuit
that is always less than V
IN. If no output capacitor is used, the
output stage of the LM3402/02HV is capable of withstanding
V
O(MAX) 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
O(MAX) indefinitely as
long as C
O is rated to handle VIN. 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
LM3402/LM3402HV
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相关代理商/技术参数 |
参数描述 |
|---|---|
| LM3402EVAL | 功能描述:BOARD EVALUATION FOR LM3402 RoHS:是 类别:编程器，开发系统 >> 评估板 - LED 驱动器 系列:PowerWise® 标准包装:1 系列:PowerWise® 电流 - 输出 / 通道:20mA 输出及类型:1，非隔离 输出电压:17V 特点:可调光 输入电压:2.7 ~ 5.5 V 已供物品:板 已用 IC / 零件:LM3508 相关产品:LM3508TLX-ND - IC LED DRVR WHT BCKLGT 9USMDLM3508TLDKR-ND - IC LED DRVR WHT BCKLGT 9MICROSMDLM3508TLCT-ND - IC LED DRVR WHT BCKLGT 9MICROSMDLM3508TLTR-ND - IC LED DRVR WHT BCKLGT 9MICROSMD |
| LM3402EVAL | 制造商:Texas Instruments 功能描述:EVAL BOARD |
| LM3402EVAL/NOPB | 功能描述:电源管理IC开发工具 LM3402 EVAL BOARD RoHS:否 制造商:Maxim Integrated 产品:Evaluation Kits 类型:Battery Management 工具用于评估:MAX17710GB 输入电压: 输出电压:1.8 V |
| LM3402HV | 制造商:Texas Instruments 功能描述:Buck Regulator ,0.5A ,LED Drivers,MSOP8 |
| LM3402HVEVAL | 功能描述:BOARD EVALUATION FOR LM3402HV RoHS:是 类别:编程器，开发系统 >> 评估板 - LED 驱动器 系列:PowerSmart® 标准包装:1 系列:PowerWise® 电流 - 输出 / 通道:20mA 输出及类型:1，非隔离 输出电压:17V 特点:可调光 输入电压:2.7 ~ 5.5 V 已供物品:板 已用 IC / 零件:LM3508 相关产品:LM3508TLX-ND - IC LED DRVR WHT BCKLGT 9USMDLM3508TLDKR-ND - IC LED DRVR WHT BCKLGT 9MICROSMDLM3508TLCT-ND - IC LED DRVR WHT BCKLGT 9MICROSMDLM3508TLTR-ND - IC LED DRVR WHT BCKLGT 9MICROSMD |
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