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
相關(guān)代理商/技術(shù)參數(shù) |
參數(shù)描述 |
LT3507IUHF#PBF |
功能描述:IC REG QD BUCK/LINEAR 38-QFN RoHS:是 類別:集成電路 (IC) >> PMIC - 穩(wěn)壓器 - 線性 + 切換式 系列:- 標(biāo)準(zhǔn)包裝:2,500 系列:- 拓?fù)?降壓(降壓)同步(3),線性(LDO)(2) 功能:任何功能 輸出數(shù):5 頻率 - 開關(guān):300kHz 電壓/電流 - 輸出 1:控制器 電壓/電流 - 輸出 2:控制器 電壓/電流 - 輸出 3:控制器 帶 LED 驅(qū)動(dòng)器:無 帶監(jiān)控器:無 帶序列發(fā)生器:是 電源電壓:5.6 V ~ 24 V 工作溫度:-40°C ~ 85°C 安裝類型:* 封裝/外殼:* 供應(yīng)商設(shè)備封裝:* 包裝:* |
LT3507IUHF#TRPBF |
功能描述:IC REG QD BUCK/LINEAR 38-QFN RoHS:是 類別:集成電路 (IC) >> PMIC - 穩(wěn)壓器 - 線性 + 切換式 系列:- 標(biāo)準(zhǔn)包裝:2,500 系列:- 拓?fù)?降壓(降壓)同步(3),線性(LDO)(2) 功能:任何功能 輸出數(shù):5 頻率 - 開關(guān):300kHz 電壓/電流 - 輸出 1:控制器 電壓/電流 - 輸出 2:控制器 電壓/電流 - 輸出 3:控制器 帶 LED 驅(qū)動(dòng)器:無 帶監(jiān)控器:無 帶序列發(fā)生器:是 電源電壓:5.6 V ~ 24 V 工作溫度:-40°C ~ 85°C 安裝類型:* 封裝/外殼:* 供應(yīng)商設(shè)備封裝:* 包裝:* |
LT3507IUHFPBF |
制造商:Linear Technology 功能描述:Triple Voltage Regulator QFN38EP |
LT3507IUHF-PBF |
制造商:LINER 制造商全稱:Linear Technology 功能描述:Triple Monolithic Step-Down Regulator with LDO |
LT3507IUHF-TRPBF |
制造商:LINER 制造商全稱:Linear Technology 功能描述:Triple Monolithic Step-Down Regulator with LDO |