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参数资料
| 型号： | LTC3454EDD#TRPBF |
| 厂商： | Linear Technology |
| 文件页数： | 7/12页 |
| 文件大小： | 0K |
| 描述： | IC LED DRIVER PHOTO FLASH 10-DFN |
| 标准包装： | 2,500 |
| 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： | 带卷 (TR) |
| 工作温度： | -40°C ~ 85°C |
LTC3454
OPERATION
Buck-Boost DC/DC Converter
The LTC3454 employs an LTC proprietary buck-boost
DC/DC converter to generate the output voltage required to
drive a high current LED. This architecture permits high-
ef?ciency, low noise operation at input voltages above,
below or equal to the output voltage by properly phasing
four internal power switches. The error amp output voltage
on the V C pin determines the duty cycle of the switches.
Since the V C pin is a ?ltered signal, it provides rejection
of frequencies well below the factory trimmed switching
frequency of 1MHz. The low R DS(ON) , low gate charge
synchronous switches provide high frequency pulse width
modulation control at high ef?ciency. Schottky diodes
across synchronous recti?er switch B and synchronous
recti?er switch D are not required, but if used do provide
a lower voltage drop during the break-before-make time
(typically 20ns), which improves peak ef?ciency by typi-
cally 1% to 2% at higher loads.
Figure 1 shows a simpli?ed diagram of how the four internal
power switches are connected to the inductor, V IN , V OUT
and GND. Figure 2 shows the regions of operation of the
buck-boost as a function of the control voltage V C . The
output switches are properly phased so transitions between
regions of operation are continuous, ?ltered and transpar-
ent to the user. When V IN approaches V OUT , the buck-boost
region is reached where the conduction time of the four
switch region is typically 150ns. Referring to Figures 1
and 2, the various regions of operation encountered as V C
increases will now be described.
Buck Mode (V IN > V OUT )
In buck mode, switch D is always on and switch C is
always off. Referring to Figure 2, when the control
each cycle. During the off time of switch A, synchronous
recti?er switch B turns on for the remainder of the cycle.
Switches A and B will alternate conducting similar to a
typical synchronous buck regulator. As the control volt-
age increases, the duty cycle of switch A increases until
the maximum duty cycle of the converter in buck mode
reaches DC BUCK |Max given by:
DC BUCK |Max = 100% – DC 4SW
where DC 4SW equals the duty cycle in % of the “four
switch” range.
DC 4SW = (150ns ? f) ? 100%
where f is the operating frequency in Hz.
Beyond this point the “four switch” or buck-boost region
is reached.
Buck-Boost or 4-Switch Mode (V IN ≈ V OUT )
Referring to Figure 2, when the control voltage V C is above
voltage V2, switch pair AD continue to operate for duty
cycle DC BUCK |max, and the switch pair AC begins to phase
in. As switch pair AC phases in, switch pair BD phases out
accordingly. When the V C voltage reaches the edge of the
buck-boost range at voltage V3, switch pair AC completely
phases out switch pair BD and the boost region begins at
duty cycle DC 4SW . The input voltage V IN where the four
switch region begins is given by:
V IN = V OUT /[1 – (150ns ? f)]
and the input voltage V IN where the four switch region
ends is given by
V IN = V OUT ? (1 – DC 4SW ) = V OUT ? [1 – (150ns ? f)]
voltage V C is above voltage V1, switch A begins to turn on
75%
D MAX
BOOST
V4 (2.1V)
V IN
9
PMOS A
SW1
SW2
V OUT
7
PMOS D
D MIN
BOOST
D MAX
BUCK
A ON, B OFF
PWM CD SWITCHES
FOUR SWITCH PWM
BOOST REGION
BUCK/BOOST REGION
V3 (1.65V)
V2 (1.55V)
10
6
D ON, C OFF
PWM AB SWITCHES BUCK REGION
NMOS B
NMOS C
0%
DUTY
V1 (0.9V)
CONTROL
3454 F01
CYCLE
3454 F02
VOLTAGE, V C
Figure 1. Simpli?ed Diagram of Internal Power Switches
Figure 2. Switch Control vs Control Voltage, V C
3454fa
7
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