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参数资料
| 型号： | LTC3454EDD#PBF |
| 厂商： | Linear Technology |
| 文件页数： | 8/12页 |
| 文件大小： | 0K |
| 描述： | IC LED DRIVER PHOTO FLASH 10-DFN |
| 标准包装： | 121 |
| 拓扑： | PWM，降压（降压），升压（升压） |
| 输出数： | 1 |
| 内部驱动器： | 是 |
| 类型 - 主要： | 背光，闪灯/白光 |
| 类型 - 次要： | 白色 LED |
| 频率： | 900kHz ~ 1.15MHz |
| 电源电压： | 2.7 V ~ 5.5 V |
| 输出电压： | 5.15V |
| 安装类型： | 表面贴装 |
| 封装/外壳： | 10-WFDFN 裸露焊盘 |
| 供应商设备封装： | 10-DFN（3x3） |
| 包装： | 管件 |
| 工作温度： | -40°C ~ 85°C |
LTC3454
APPLICATIONS INFORMATION
Boost Mode (V IN < V OUT )
In boost mode, switch A is always on and switch B is always
off. Referring to Figure 2, when the control voltage V C is
above voltage V3, switches C and D will alternate conduct-
ing similar to a typical synchronous boost regulator. The
maximum duty cycle of the converter is limited to 88%
typical and is reached when V C is above V4.
Forward Current Limit
If the current delivered from V IN through PMOS switch A
exceeds 3.4A (typical), switch A is shut off immediately.
Switches B and D are turned on for the remainder of the
cycle in order to safely discharge the forward inductor
current at the maximum rate possible.
Reverse Current Limit
If the current delivered from V OUT backwards through
PMOS switch D exceeds 275mA (typical), switch D is
shut off immediately. Switches A and C are turned on for
the remainder of the cycle in order to safely discharge the
reverse inductor current at the maximum rate possible.
Undervoltage Lockout
To prevent operation of the power switches at high R DS(ON) ,
an undervoltage lockout is incorporated on the LTC3454.
When the input supply voltage drops below approximately
1.90V, the four power switches and all control circuitry are
turned off except for the undervoltage block, which draws
a few microamperes.
limiting the rate of duty cycle change as V C transitions
from the buck region through the buck-boost region into
the boost region. Once the soft-start times out, it can only
be reset by entering shutdown, or by an undervoltage or
overtemperature condition.
Autozero Error Amp
The error ampli?er is an autozeroing transconductance
amp with source and sink capability. The output of this
ampli?er drives a capacitor to GND at the V C pin. This
capacitor sets the dominant pole for the regulation loop.
(See the Applications Information section for selecting
the capacitor value). The feedback signal to the error
amp is developed across a resistor through which LED
current ?ows.
Safety Error Amp
The safety error ampli?er is a transconductance ampli?er
with sink only capability. In normal operation, it has no
effect on the loop regulation. However, if the LED pin open-
circuits, the output voltage will keep rising, and the safety
error amp will eventually take over control of the regulation
loop to prevent V OUT runaway. The V OUT threshold at which
this occurs is approximately 5.15V.
LED Current Programming and Enable Circuit
Two enable pins work in conjunction with dual external
resistors to program LED current to one of three nonzero
settings. The table below explains how the current can
be set.
Overtemperature Protection
If the junction temperature of the LTC3454 exceeds 130°C
for any reason, all four switches are shut off immediately.
The overtemperature protection circuit has a typical hys-
teresis of 11°C.
EN1
GND
V IN
GND
V IN
EN2
GND
GND
V IN
V IN
I LOAD (A)
0 (SHUTDOWN)
3850 ? 0.8V/R ISET1
3850 ? 0.8V/R ISET2
3850 ? (0.8V/R ISET1 + 0.8V/R ISET2 )
Soft-Start
The LTC3454 includes an internally ?xed soft-start which
is active when powering up or coming out of shutdown.
The soft-start works by clamping the voltage on the V C
node and gradually releasing it such that it requires 200μs
to linearly slew from 0.9V to 2.1V. This has the effect of
With either enable pin pulled high, the buck-boost will
regulate the output voltage at the current programmed
by R ISET1 and/or R ISET2 .
With both enable pins pulled to GND, the LTC3454 is in
shutdown and draws zero current. The enable pins are
high impedance inputs and should not be ?oated.
3454fa
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