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2005 Microchip Technology Inc.
DS21974A-page 17
TC1313
5.5
Inductor Selection
For most applications, a 4.7 μH inductor is recom-
mended to minimize noise. There are many different
magnetic core materials and package options to select
from. That decision is based on size, cost and
acceptable radiated energy levels. Toroid and shielded
ferrite pot cores will have low radiated energy but tend
to be larger and more expensive. With a typical
2.0 MHz switching frequency, the inductor ripple
current can be calculated based on the following
formulas.
EQUATION 5-2:
Duty cycle represents the percentage of switch-on
time.
EQUATION 5-3:
The inductor ac ripple current can be calculated using
the following relationship:
EQUATION 5-4:
Solving for
Δ
I
L
= yields:
EQUATION 5-5:
When considering inductor ratings, the maximum DC
current rating of the inductor should be at least equal to
the maximum buck regulator load current (I
OUT1
), plus
one half of the peak-to-peak inductor ripple current
(1/2 *
Δ
I
L
). The inductor DC resistance can add to the
buck converter I
2
R losses. A rating of less than 200 m
Ω
is recommended. Overall efficiency will be improved by
using lower DC resistance inductors.
TABLE 5-2:
TC1313 RECOMMENDED
INDUCTOR VALUES
5.6
Thermal Calculations
5.6.1
BUCK REGULATOR OUTPUT
(V
OUT1
)
The TC1313 is available in two different 10-pin
packages (MSOP and 3X3 DFN). By calculating the
power dissipation and applying the package thermal
resistance, (
θ
JA
), the junction temperature is estimated.
The maximum continuous junction temperature rating
for the TC1313 is +125°C.
To quickly estimate the internal power dissipation for
the switching buck regulator, an empirical calculation
using measured efficiency can be used. Given the
measured efficiency (
Section 2.0 “Typical Perfor-
mance Curves”
), the internal power dissipation is
estimated below.
EQUATION 5-6:
V
Efficiency
The first term is equal to the input power (definition of
efficiency, P
OUT
/P
IN
=
Efficiency). The second term is
equal to the delivered power. The difference is internal
power dissipation. This estimate assumes that most of
the power lost is internal to the TC1313. There is some
percentage of power lost in the buck inductor, with very
little loss in the input and output capacitors.
DutyCycle
V
V
IN
-------------
=
T
ON
DutyCycle
F
SW
---------
×
=
Where:
F
SW
= Switching Frequency.
V
L
L
Δ
I
L
Δ
t
--------
×
=
Where:
V
L
= voltage across the inductor (V
IN
– V
OUT
)
Δ
t = on-time of P-channel MOSFET
Δ
I
L
V
L
L
-----
Δ
t
×
=
Part
Number
Value
(μH)
DCR
Ω
(
max)
MAX
I
DC
(A)
Size
WxLxH (mm)
Coiltronics
SD10
SD10
SD10
Coiltronics
SD12
SD12
SD12
Sumida Corporation
CMD411
CMD411
CMD411
Coilcraft
1008PS
1812PS
2.2
3.3
4.7
0.091
0.108
0.154
1.35
1.24
1.04
5.2, 5.2, 1.0 max.
5.2, 5.2, 1.0 max.
5.2, 5.2, 1.0 max.
2.2
3.3
4.7
0.075
0.104
0.118
1.80
1.42
1.29
5.2, 5.2, 1.2 max.
5.2, 5.2, 1.2 max.
5.2, 5.2, 1.2 max.
2.2
3.3
4.7
0.116
0.174
0.216
0.950 4.4, 5.8, 1.2 max.
0.770 4.4, 5.8, 1.2 max.
0.750 4.4, 5.8, 1.2 max.
4.7
4.7
0.35
0.11
1.0
1.15
3.8, 3.8, 2.74 max.
5.9, 5.0, 3.81 max.
-------------------------------------
V
OUT1
I
OUT1
×
(
)
–
P
Dissipation
=
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相關(guān)代理商/技術(shù)參數(shù) |
參數(shù)描述 |
|---|---|
| TC1313-DG0EMF | 功能描述:低壓差穩(wěn)壓器 - LDO PWM/LDO combo RoHS:否 制造商:Texas Instruments 最大輸入電壓:36 V 輸出電壓:1.4 V to 20.5 V 回動(dòng)電壓（最大值）:307 mV 輸出電流:1 A 負(fù)載調(diào)節(jié):0.3 % 輸出端數(shù)量: 輸出類型:Fixed 最大工作溫度:+ 125 C 安裝風(fēng)格:SMD/SMT 封裝 / 箱體:VQFN-20 |
| TC1313-DG0EMFTR | 功能描述:低壓差穩(wěn)壓器 - LDO PWM/LDO combo RoHS:否 制造商:Texas Instruments 最大輸入電壓:36 V 輸出電壓:1.4 V to 20.5 V 回動(dòng)電壓（最大值）:307 mV 輸出電流:1 A 負(fù)載調(diào)節(jié):0.3 % 輸出端數(shù)量: 輸出類型:Fixed 最大工作溫度:+ 125 C 安裝風(fēng)格:SMD/SMT 封裝 / 箱體:VQFN-20 |
| TC1313-PP0EMF | 功能描述:低壓差穩(wěn)壓器 - LDO PWM LDO combo PG RoHS:否 制造商:Texas Instruments 最大輸入電壓:36 V 輸出電壓:1.4 V to 20.5 V 回動(dòng)電壓（最大值）:307 mV 輸出電流:1 A 負(fù)載調(diào)節(jié):0.3 % 輸出端數(shù)量: 輸出類型:Fixed 最大工作溫度:+ 125 C 安裝風(fēng)格:SMD/SMT 封裝 / 箱體:VQFN-20 |
| TC1313-PP0EMFTR | 功能描述:低壓差穩(wěn)壓器 - LDO PWM LDO combo PG RoHS:否 制造商:Texas Instruments 最大輸入電壓:36 V 輸出電壓:1.4 V to 20.5 V 回動(dòng)電壓（最大值）:307 mV 輸出電流:1 A 負(fù)載調(diào)節(jié):0.3 % 輸出端數(shù)量: 輸出類型:Fixed 最大工作溫度:+ 125 C 安裝風(fēng)格:SMD/SMT 封裝 / 箱體:VQFN-20 |
| TC1313-RD1EMF | 功能描述:低壓差穩(wěn)壓器 - LDO PWM/LDO combo RoHS:否 制造商:Texas Instruments 最大輸入電壓:36 V 輸出電壓:1.4 V to 20.5 V 回動(dòng)電壓（最大值）:307 mV 輸出電流:1 A 負(fù)載調(diào)節(jié):0.3 % 輸出端數(shù)量: 輸出類型:Fixed 最大工作溫度:+ 125 C 安裝風(fēng)格:SMD/SMT 封裝 / 箱體:VQFN-20 |
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