LT3507
14
3507fa
maximum duty cycle. The boost circuit also limits the
minimum input voltage for proper start-up. If the input
voltage ramps slowly, or the LT3507 turns on when the
output is already in regulation, the boost capacitor may
not be fully charged. Because the boost capacitor charges
with the energy stored in the inductor, the circuit will rely
on some minimum load current to get the boost circuit
running properly. This minimum load will depend on
input and output voltages, and on the arrangement of
the boost circuit. The minimum load current generally
goes to zero once the circuit has started. Figure 4 shows
a plot of minimum load to start and to run as a function
of input voltage. Even without an output load current, in
many cases the discharged output capacitor will present
a load to the switcher that will allow it to start.
The boost current is generally small but can become signi -
cant at high duty cycles. The required boost current is:
I
BOOST
=
V
OUT
V
IN
?/DIV>
?/DIV>
?/DIV>
?/DIV>
?/DIV>
?/DIV>
I
OUT
40
?/DIV>
?/DIV>
?/DIV>
?/DIV>
?/DIV>
?/DIV>
Converter with Backup Output Regulator
There is another situation to consider in systems where
the output will be held high when the input to the LT3507
is absent. If the V
IN
and one of the RUN pins are allowed
APPLICATIONS INFORMATION
Figure 3. Generating the Boost Voltage
Figure 4. The Minimum Input Voltage Depends on Output Voltage, Load Current and Boost Circuit
V
IN
BOOST
GND
SW
V
IN
LT3507
(3a)
D2
V
OUT
C3
V
BOOST
V
SW
E V
OUT
MAX V
BOOST
E V
IN
+ V
OUT
V
IN
BOOST
GND
SW
V
IN
LT3507
(3b)
D2
V
OUT
C3
V
BOOST
V
SW
E V
IN
MAX V
BOOST
E 2V
IN
3507 F03
D2
V
IN
BOOST
GND
SW
V
IN
LT3507
(3c)
V
OUT
V
BOOST
V
SW
E V
INB
MAX V
BOOST
E V
INB
+ V
IN
MINIMUM VALUE FOR V
INB
= 3V
V
INB
> 3V
C3
LOAD CURRENT (A)
0.001
5.5
5.0
4.0
3.0
4.5
3.5
2.5
3507 F04b
1.000
0.010
0.100
T
A
= 25癈
V
OUT
= 3.3V
TO START
TO RUN
LOAD CURRENT (A)
0.001
8.0
7.5
6.5
5.5
4.5
7.0
6.0
5.0
4.0
3507 F04a
1.000
0.010
0.100
T
A
= 25癈
V
OUT
= 5V
TO START
TO RUN
发布紧急采购，3分钟左右您将得到回复。
相关PDF资料
LT3570IFE#TRPBF
IC REG BUCK/BST/LINEAR 20TSSOP
LT3645HMSE#TRPBF
IC REG DL BUCK/LINEAR 12-MSOP
LT3694IFE-1#TRPBF
IC REG TRPL BUCK/LINEAR 20TSSOP
LT4220IGN#TR
IC CTLR HOTSWAP DUAL 16-SSOP
LT4250LCN8
IC CONTRLR HOT SWAP NEG 48V 8DIP
LT4254CGN
IC CTRLR HOTSWAP POSVOLT 16SSOP
LT4256-1IS8#TRPBF
IC CTRLR HOTSWAP HV LATCH 8SOIC
LTC1392IS8#TRPBF
IC DATA ACQ SYSTEM 10BIT 8-SOIC
相关代理商/技术参数
LT3507HUHF-PBF
制造商:LINER 制造商全称:Linear Technology 功能描述:Triple Monolithic Step-Down Regulator with LDO
LT3507HUHF-TRPBF
制造商:LINER 制造商全称:Linear Technology 功能描述:Triple Monolithic Step-Down Regulator with LDO
LT3507IUHF#PBF
功能描述:IC REG QD BUCK/LINEAR 38-QFN RoHS:是 类别:集成电路 (IC) >> PMIC - 稳压器 - 线性 + 切换式 系列:- 标准包装:2,500 系列:- 拓扑:降压（降压）同步（3），线性（LDO）（2） 功能:任何功能 输出数:5 频率 - 开关:300kHz 电压/电流 - 输出 1:控制器 电压/电流 - 输出 2:控制器 电压/电流 - 输出 3:控制器 带 LED 驱动器:无 带监控器:无 带序列发生器:是 电源电压:5.6 V ~ 24 V 工作温度:-40°C ~ 85°C 安装类型:* 封装/外壳:* 供应商设备封装:* 包装:*
LT3507IUHF#TRPBF
功能描述:IC REG QD BUCK/LINEAR 38-QFN RoHS:是 类别:集成电路 (IC) >> PMIC - 稳压器 - 线性 + 切换式 系列:- 标准包装:2,500 系列:- 拓扑:降压（降压）同步（3），线性（LDO）（2） 功能:任何功能 输出数:5 频率 - 开关:300kHz 电压/电流 - 输出 1:控制器 电压/电流 - 输出 2:控制器 电压/电流 - 输出 3:控制器 带 LED 驱动器:无 带监控器:无 带序列发生器:是 电源电压:5.6 V ~ 24 V 工作温度:-40°C ~ 85°C 安装类型:* 封装/外壳:* 供应商设备封装:* 包装:*
LT3507IUHFPBF
制造商:Linear Technology 功能描述:Triple Voltage Regulator QFN38EP
LT3507IUHF-PBF
制造商:LINER 制造商全称:Linear Technology 功能描述:Triple Monolithic Step-Down Regulator with LDO
LT3507IUHF-TRPBF
制造商:LINER 制造商全称:Linear Technology 功能描述:Triple Monolithic Step-Down Regulator with LDO
LT3508
制造商:LINER 制造商全称:Linear Technology 功能描述:Dual Monolithic 1.4A Step-Down Switching Regulator