參數(shù)資料
型號(hào)： LT3509EDE#TRPBF
廠商： LINEAR TECHNOLOGY CORP
元件分類： 穩(wěn)壓器
英文描述： 1.2 A DUAL SWITCHING CONTROLLER, 2500 kHz SWITCHING FREQ-MAX, PDSO14
封裝： 4 X 3 MM, LEAD FREE, PLASTIC, MO-229WGED-3, DFN-14
文件頁(yè)數(shù)： 3/24頁(yè)
文件大?。?/td> 271K
代理商： LT3509EDE#TRPBF
LT3509
11
3509fc
APPLICATIONS INFORMATION
In any step-down switcher the duty cycle when operating
in continuous, or xed frequency, mode is dependent
on the step-down ratio. This is because for a constant
average load current the decay of the inductor current
when the switch is off must match the increase in inductor
current when the switch is on. The can be estimated by
the following formula:
DC
VV
V
OUT
F
IN
SW
F
=
+
+
where:
DC = Duty Cycle (Fraction of Cycle when Switch is On)
VOUT = Output Voltage
VIN = Input Voltage
VF = Catch Diode Forward Voltage
VSW = Switch Voltage Drop
Note: This formula neglects switching and inductor losses
so in practice the duty cycle may be slightly higher.
It is clear from this equation that the duty cycle will approach
100% as the input voltage is reduced and become smaller
as the input voltage increases. There are practical limits to
the minimum and maximum duty cycles for continuous
operation due to the switch minimum off and on times.
These are independent of operating frequency so it is clear
that range of usable duty cycle is inverserly proportional to
frequency. Therefore at higher frequency the input voltage
range (for constant frequency operation) will narrow.
The minimum duty cycle is given by:
DC
f
t
MIN
SW
ON MIN
=
()
where:
fSW = Switching Frequency
tON(MIN) = Switch Minimum On-Time
The minimum on time increases with increasing tempera-
ture so the value for the maximum operating temperature
should be used. See the Minimum On-Time vs Temperature
graph in the Typical Performance Characteristics.
The maximum input voltage for this duty cycle is given by:
V
VV
DC
VV
IN MAX
OUT
F
MIN
FSW
() =
+
+
Above this voltage the only way the LT3509 can maintain
regulation is to skip cycles so the effective frequency will
reduce. This will cause an increase in ripple and the switch-
ing noise will shift to a lower frequency. This calculation
will in practice drive the maximum switching frequency
for a desired step-down ratio.
Figure 3. Continuous Mode
IL
0.5A/DIV
VOUT
100mV/DIV
(AC COUPLED)
TIME 1μs/DIV
3509 F03
Figure 4. Pulse Skipping
IL
0.5A/DIV
VOUT
100mV/DIV
(AC COUPLED)
TIME 1μs/DIV
3509 F04
相關(guān)PDF資料
PDF描述
LT3570EFE#TRPBF 3.1 A SWITCHING REGULATOR, 2750 kHz SWITCHING FREQ-MAX, PDSO20
LT3570IUF#PBF 3.1 A SWITCHING REGULATOR, 2750 kHz SWITCHING FREQ-MAX, PQCC24
LT3570EFE#PBF 3.1 A SWITCHING REGULATOR, 2750 kHz SWITCHING FREQ-MAX, PDSO20
LT3570IUF#TRPBF 3.1 A SWITCHING REGULATOR, 2750 kHz SWITCHING FREQ-MAX, PQCC24
LT3570EUF#TRPBF 3.1 A SWITCHING REGULATOR, 2750 kHz SWITCHING FREQ-MAX, PQCC24
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