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参数资料
| 型号： | LT3475EFE-1#PBF |
| 厂商： | Linear Technology |
| 文件页数： | 7/20页 |
| 文件大小： | 0K |
| 描述： | IC LED DRVR HP CONS CURR 20TSSOP |
| 标准包装： | 74 |
| 恒定电流： | 是 |
| 拓扑： | PWM，降压（降压） |
| 输出数： | 2 |
| 内部驱动器： | 是 |
| 类型 - 主要： | 车载，背光 |
| 类型 - 次要： | 颜色，白色 LED |
| 频率： | 200kHz ~ 2MHz |
| 电源电压： | 3.7 V ~ 36 V |
| 安装类型： | 表面贴装 |
| 封装/外壳： | 20-TSSOP（0.173"，4.40mm 宽）裸露焊盘 |
| 供应商设备封装： | 20-TSSOP-EP |
| 包装： | 管件 |
| 工作温度： | -40°C ~ 85°C |
LT3475/LT3475-1
OPERATION
The LT3475 is a dual constant frequency, current mode
regulator with internal power switches capable of gen-
erating constant 1.5A outputs. Operation can be best
understood by referring to the Block Diagram.
If the SHDN pin is tied to ground, the LT3475 is shut
down and draws minimal current from the input source
tied to V IN . If the SHDN pin exceeds 1V, the internal bias
circuits turn on, including the internal regulator, reference
and oscillator. The switching regulators will only begin to
operate when the SHDN pin exceeds 2.6V.
The switcher is a current mode regulator. Instead of directly
modulating the duty cycle of the power switch, the feedback
loop controls the peak current in the switch during each
cycle. Compared to voltage mode control, current mode
control improves loop dynamics and provides cycle-by-
cycle current limit.
A pulse from the oscillator sets the RS ?ip-?op and turns
on the internal NPN bipolar power switch. Current in the
switch and the external inductor begins to increase. When
this current exceeds a level determined by the voltage at
V C , current comparator C1 resets the ?ip-?op, turning
off the switch. The current in the inductor ?ows through
the external Schottky diode and begins to decrease. The
cycle begins again at the next pulse from the oscillator.
In this way, the voltage on the V C pin controls the current
through the inductor to the output. The internal error
ampli?er regulates the output current by continually
adjusting the V C pin voltage. The threshold for switching
on the V C pin is 0.8V, and an active clamp of 1.8V limits
the output current.
The voltage on the V ADJ pin sets the current through the
LED pin. The NPN, Q3, pulls a current proportional to the
voltage on the V ADJ pin through the 100Ω resistor. The gm
ampli?er servos the V C pin to set the current through the
0.067Ω resistor and the LED pin. When the voltage drop
across the 0.067Ω resistor is equal to the voltage drop
across the 100Ω resistor, the servo loop is balanced.
Tying the REF pin to the V ADJ pin sets the LED pin current
to 1.5A. Tying a resistor divider to the REF pin allows the
programming of LED pin currents of less than 1.5A. LED
pin current can also be programmed by tying the V ADJ pin
directly to a voltage source.
An LED can be dimmed with pulse width modulation
using the PWM pin and an external NFET. If the PWM
pin is unconnected or is pulled high, the part operates
nominally. If the PWM pin is pulled low, the V C pin is dis-
connected from the internal circuitry and draws minimal
current from the compensation capacitor. Circuitry draw-
ing current from the OUT pin is also disabled. This way,
the V C pin and the output capacitor store the state of
the LED pin current until the PWM is pulled high again.
This leads to a highly linear relationship between pulse
width and output light, allowing for a large and accurate
dimming range.
The R T pin allows programming of the switching frequency.
For applications requiring the smallest external components
possible, a fast switching frequency can be used. If low
dropout or very high input voltages are required, a slower
switching frequency can be programmed.
During startup V OUT will be at a low voltage. The NPN,
Q3, can only operate correctly with suf?cient voltage
of ≈1.7V at V OUT , A comparator senses V OUT and forces
the V C pin high until V OUT rises above 2V, and Q3 is op-
erating correctly.
The switching regulator performs frequency foldback
during overload conditions. An ampli?er senses when
V OUT is less than 2V and begins decreasing the oscillator
frequency down from full frequency to 15% of the nominal
frequency when V OUT = 0V. The OUT pin is less than 2V
during startup, short circuit, and overload conditions.
Frequency foldback helps limit switch current under these
conditions.
The switch driver operates either from V IN or from the
BOOST pin. An external capacitor and Schottky diode
are used to generate a voltage at the BOOST pin that
is higher than the input supply. This allows the driver
to saturate the internal bipolar NPN power switch for
ef?cient operation.
3475fb
7
相关PDF资料 |
PDF描述 |
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| LT3476EUHF#PBF | IC LED DRVR HP CONST CURR 38-QFN |
| LT3477EFE#PBF | IC LED DRVR HP CONS CURR 20TSSOP |
| LT3478IFE#PBF | IC LED DRVR HP CONS CURR 16TSSOP |
| LT3486EFE#PBF | IC LED DRVR WHITE BCKLGT 16TSSOP |
| LT3491EDC#TRMPBF | IC LED DRIVER WHITE BCKLGT 6-DFN |
相关代理商/技术参数 |
参数描述 |
|---|---|
| LT3475EFE-1-TRPBF | 制造商:LINER 制造商全称:Linear Technology 功能描述:Dual Step-Down l 1.5A LED Driver |
| LT3475EFEPBF | 制造商:Linear Technology 功能描述:Dual Step-Down 1.5A LED Driver,LT3475 |
| LT3475EFE-PBF | 制造商:LINER 制造商全称:Linear Technology 功能描述:Dual Step-Down l 1.5A LED Driver |
| LT3475EFE-TRPBF | 制造商:LINER 制造商全称:Linear Technology 功能描述:Dual Step-Down l 1.5A LED Driver |
| LT3475FE-1 | 制造商:LINER 制造商全称:Linear Technology 功能描述:Dual Step-Down l 1.5A LED Driver |
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