參數(shù)資料
型號(hào)： LT3509IMSE#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, PDSO16
封裝： LEAD FREE, PLASTIC, MSOP-16
文件頁(yè)數(shù)： 6/24頁(yè)
文件大?。?/td> 271K
代理商： LT3509IMSE#TRPBF
LT3509
14
3509fc
When the switch is off, the potential across the inductor is
the output voltage plus the catch diode forward voltage. This
gives the peak-to-peak ripple current in the inductor:
ΔIL =(1– DC)
V
OUT + VF
Lf
SW
where:
DC = Duty Cycle
fSW = Switching Frequency
L = Inductor Value
VF = Diode Forward Voltage
The peak inductor and switch current is:
I
SWPK =ILPK =IOUT +
ΔIL
2
To maintain output regulation, this peak current must be
less than the LT3509’s switch current limit ILIM. This is
dependent on duty cycle due to the slope compensation.
For ILIM is at least 1.4A at low duty cycles and decreases
linearly to 1.0A at DC = 0.8.
The theoretical minimum inductance can now be calcu-
lated as:
L
DC
f
VV
II
MIN
OUT
F
LIM
OUT
=
+
1–
–
where DCMIN is the minimum duty cycle called for by the
application i.e.:
DC
VV
V
MIN
OUT MAX
F
IN MIN
SW
F
=
+
()
() –
There is a limit to the actual minimum duty cycle imposed
by the minimum on-time of the switch. For a robust design
it is important that inductor that will not saturate when
the switch is at its minimum on-time, the input voltage
is at maximum and the output is short circuited. In this
case the full input voltage, less the drop in the switch, will
appear across the inductor. This doesn’t require an actual
short, just starting into a capacitive load will provide the
same conditions. The Diode current sensing scheme will
ensure that the switch will not turn-on if the inductor
current is above the DA current limit threshold, which has
a maximum of 1.1A. The peak current under short-circuit
conditions can then be calculated from:
I
Vt
L
A
PEAK
IN
ON MIN
=+
.
()
11
The inductor should have a saturation current greater than
this value. For safe operation with high input voltages this
can often mean using a physically larger inductor as higher
value inductors often have lower saturation currents for
a given core size. As a general rule the saturation current
should be at least 1.8A to be short-circuit proof. However, it’s
generally better to use an inductor larger than the minimum
value. For robust operation at input voltages greater than
30V, use an inductor with a value of 4.2μH or greater, and
a saturation current rating of 1.8A or higher. The minimum
inductor has large ripple currents which increase core
losses and require large output capacitors to keep output
voltage ripple low. Select an inductor greater than LMIN
that keeps the ripple current below 30% of ILIM.
APPLICATIONS INFORMATION
相關(guān)PDF資料
PDF描述
LT3509EMSE#TRPBF 1.2 A DUAL SWITCHING CONTROLLER, 2500 kHz SWITCHING FREQ-MAX, PDSO16
LT3509IDE#TRPBF 1.2 A DUAL SWITCHING CONTROLLER, 2500 kHz SWITCHING FREQ-MAX, PDSO14
LT3509IDE#PBF 1.2 A DUAL SWITCHING CONTROLLER, 2500 kHz SWITCHING FREQ-MAX, PDSO14
LT3509EDE#PBF 1.2 A DUAL SWITCHING CONTROLLER, 2500 kHz SWITCHING FREQ-MAX, PDSO14
LT3509EDE#TRPBF 1.2 A DUAL SWITCHING CONTROLLER, 2500 kHz SWITCHING FREQ-MAX, PDSO14
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