參數(shù)資料
型號(hào)： LT3581IDE#TRPBF
廠商： LINEAR TECHNOLOGY CORP
元件分類(lèi)： 穩(wěn)壓器
英文描述： SWITCHING REGULATOR, PDSO14
封裝： 4 X 3 MM, 0.75 MM HEIGHT, LEAD FREE, PLASTIC, MO-229WGED-3, DFN-14
文件頁(yè)數(shù)： 10/36頁(yè)
文件大?。?/td> 498K
代理商： LT3581IDE#TRPBF
LT3581
3581f
applicaTions inForMaTion
where TJ = Die Junction Temperature, TA = Ambient Tem-
perature, PTOTAL is the final result from the calculations
shown in Table 4, and
θJA is the thermal resistance from
the silicon junction to the ambient air.
Thepublished(http://www.linear.com/designtools/packag-
ing/Linear_Technology_Thermal_Resistance_Table.pdf)
θJA value is 43°C/W for the 4mm × 3mm 14-pin DFN
package and 45°C/W for the 16-lead MSOP package. In
practice, lower
θJA values are realizable if board layout is
performedwithappropriategrounding(accountingforheat
sinking properties of the board) and other considerations
listed in the Layout Guidelines section. For instance, a
θJA value of ~24°C/W was consistently achieved for both
MSE and DFN packages of the LT3581 (at VIN= 5V, VOUT =
12V, IOUT = 0.83A, fOSC = 2MHz) when board layout was
optimized as per the suggestions in the Board Layout
Guidelines section.
Junction Temperature Measurement
The duty cycle of the CLKOUT signal is linearly propor-
tional to die junction temperature, TJ. To get a temperature
reading, measure the duty cycle of the CLKOUT signal and
use the following equation to approximate the junction
temperature:
T
DC
J
CLKOUT
=
– %
. %
35
0 3
where DCCLKOUT is the CLKOUT duty cycle in % and TJ
is the die junction temperature in °C. Although the actual
die temperature can deviate from the above equation by
±15°C, the relationship between change in CLKOUT duty
cycle and change in die temperature is well defined. Basi-
cally a 1% change in CLKOUT duty cycle corresponds to a
3.33°C change in die temperature. Note that the CLKOUT
pin is only meant to drive capacitive loads up to 50pF.
Thermal Lockout
A fault condition occurs when the die temperature exceeds
165°C (see Operation Section), and the part goes into
thermal lockout. The fault condition ceases when the die
temperature drops by ~5°C (nominal).
SWITCHING FREQUENCY
There are several considerations in selecting the operat-
ing frequency of the converter. The first is staying clear
of sensitive frequency bands, which cannot tolerate any
spectral noise. For example, in products incorporating RF
communications, the 455kHz IF frequency is sensitive to
any noise, therefore switching above 600kHz is desired.
Some communications have sensitivity to 1.1MHz and in
that case a 1.5MHz switching converter frequency may be
employed. The second consideration is the physical size
of the converter. As the operating frequency goes up, the
inductor and filter capacitors go down in value and size.
The tradeoff is efficiency, since the losses due to switch-
ing dynamics (see Thermal Considerations), Schottky
diode charge, and other capacitive loss terms increase
proportionally with frequency.
Oscillator Timing Resistor (RT)
The operating frequency of the LT3581 can be set by the
internalfree-runningoscillator.WhentheSYNCpinisdriven
low (< 0.4V), the frequency of operation is set by a resistor
from the RT pin to ground. An internally trimmed timing
capacitor resides inside the IC. The oscillator frequency
is calculated using the following formula:
f
R
OSC
T
=
+
87 6
1
.
where fOSC is in MHz and RT is in k. Conversely, RT (in k)
can be calculated from the desired frequency (in MHz)
using:
R
f
T
OSC
=
87 6
1
.
–
相關(guān)PDF資料
PDF描述
LT3581IMSE#TRPBF SWITCHING REGULATOR, PDSO16
LT3581IMSE#PBF SWITCHING REGULATOR, PDSO16
LT3581IDE#PBF SWITCHING REGULATOR, PDSO14
LT3682IDD#TRPBF SWITCHING REGULATOR, PDSO12
LT3682EDD#TRPBF SWITCHING REGULATOR, PDSO12
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