参数资料
型号: LT3503EDCB
厂商: LINEAR TECHNOLOGY CORP
元件分类: 稳压器
英文描述: 1 A SWITCHING REGULATOR, 2400 kHz SWITCHING FREQ-MAX, PDSO6
封装: 2 X 3 MM, PLASTIC, MO-229, DFN-6
文件页数: 5/20页
文件大小: 423K
代理商: LT3503EDCB
13
LT3503
3503f
The minimum operating voltage of an LT3503 application
is limited by the undervoltage lockout (3.6V) and by the
maximum duty cycle as outlined above. For proper start-
up, the minimum input voltage is also limited by the boost
circuit. If the input voltage is ramped slowly, or the LT3503
is turned on with its SHDN pin when the output is already
in regulation, then the boost capacitor may not be fully
charged. Because the boost capacitor is charged 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 the input and
output voltages, and on the arrangement of the boost
circuit. The minimum load generally goes to zero once the
circuit has started. Figure 7 shows a plot of minimum load
APPLICATIO S I FOR ATIO
WU
U
to start and to run as a function of input voltage. In many
cases the discharged output capacitor will present a load
to the switcher which will allow it to start. The plots show
the worst-case situation where VIN is ramping verly slowly.
For lower start-up voltage, the boost diode can be tied to
VIN; however this restricts the input range to one-half of
the absolute maximum rating of the BOOST pin.
At light loads, the inductor current becomes discontinu-
ous and the effective duty cycle can be very high. This
reduces the minimum input voltage to approximately
400mV above VOUT. At higher load currents, the inductor
current is continuous and the duty cycle is limited by the
maximum duty cycle of the LT3503, requiring a higher
input voltage to maintain regulation.
(7a) Typical Minimum Input Voltage,
VOUT = 5V
(7b) Typical Minimum Input Voltage,
VOUT = 3.3V
Figure 7
Figure 6. Two Circuits for Generating the Boost Voltage
VIN
BOOST
GND
SW
VIN
LT3503
(6a)
D2
VOUT
C3
VBOOST – VSW VOUT
MAX VBOOST VIN + VOUT
3503 F06a
VIN
BOOST
GND
SW
VIN
LT3503
(6b)
D2
3503 F06b
VOUT
C3
VBOOST – VSW VIN
MAX VBOOST 2VIN
LOAD CURRENT (mA)
1
5.2
INPUT
VOLTAGE
(V)
6.7
7.2
7.7
10
100
1000
3503 F07a
6.2
5.7
TO START
TO RUN
LOAD CURRENT (mA)
1
INPUT
VOLTAGE
(V)
5.0
5.5
TO START
TO RUN
10
1OO
1000
3503 F07b
4.5
4.0
3.5
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