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參數(shù)資料
| 型號： | MIC2142BM5 |
| 廠商： | MICREL INC |
| 元件分類： | 穩(wěn)壓器 |
| 英文描述： | Micropower Boost Converter |
| 中文描述： | SWITCHING REGULATOR, 365 kHz SWITCHING FREQ-MAX, PDSO5 |
| 封裝： | SOT-23, 5 PIN |
| 文件頁數(shù)： | 7/17頁 |
| 文件大小： | 137K |
| 代理商： | MIC2142BM5 |
December 2000
7
MIC2142
MIC2142
Application Information
Predesigned circuit information is at the end of this section.
Component Selection
Resistive Divider (Adjustable Version)
The external resistive divider should divide the output voltage
down to the nominal reference voltage. Current drawn through
this resistor string should be limited in order to limit the effect
on the overall efficiency. The maximum value of the resistor
string is limited by the feedback input bias current and the
potential for noise being coupled into the feedback pin. A
resistor string on the order of 2M
limits the additional load
on the output to 20
μ
A for a 20V output. In addition, the
feedback input bias current error would add a nominal 60mV
error to the expected output. Equation 1 can be used for
determining the values for R2 and R1.
Micrel
(1)
V
R1 R2
R1
V
OUT
REF
=
Boost Inductor
Maximum power is delivered to the load when the oscillator
is gated on100% of the time. Total output power and circuit
efficiency must be considered when determining the maxi-
mum inductor value. The largest inductor possible is prefer-
able in order to minimize the peak current and output ripple.
Efficiency can vary from 80% to 90% depending upon input
voltage, output voltage, load current, inductor, and output
diode.
Equation 2 solves for the output current capability for a given
inductor value and expected efficiency. Figures 7 through 12
show estimates for maximum output current assuming the
minimum duty and maximum frequency and 80% efficiency.
To determine the necessary inductance, find the intersection
between the output voltage and current, and then select the
value of the inductor curve just above the intersection. If the
efficiency is expected to be different than the 85% used for the
graph, Equation 2 can then be used to better determine the
maximum output capability.
The peak inductor/switch current can be calculated from
Equation 3 or read from the graph in Figure 13. The peak
current shown in the graph in Figure 13 is derived assuming
a max duty cycle and a minimum frequency. The selected
inductor and diode peak current capability must be greater
than this. The peak current seen by the inductor is calculated
at the maximum input voltage. A wide ranging input voltage
will result in a higher worst case peak current in the inductor
than a narrow input range.
)
(2)
I
V
2L
T
V
eff
V
O(max)
IN(min) ON
MAX
S
O
IN min
=
(
×
)
2
1
(3)
I
t
V
L
PK
ON max
IN max
MIN
=
)
)
Table 1 lists common inductors suitable for most applica-
tions. Due to the internal transistor peak current limitation at
low input voltages, inductor values less than 10
μ
H are not
recommmended. Table 6 lists minimum inductor sizes versus
input and output voltage. In low-cost, low-peak-current appli-
cations, RF-type leaded inductors may sufficient. All induc-
tors listed in Table 5 can be found within the selection of
CR32- or LQH4C-series inductors from either Sumida or
muRata.
r
e
r
u
t
a
R
d
m
r
M
.
t
C
a
u
u
M
u
S
W
.
n
a
M
s
C
2
F
0
e
e
3
C
1
R
C
8
7
9
S
e
t
u
t
u
d
e
d
e
p
y
o
o
d
d
T
m
m
a
a
e
e
e
c
e
a
s
a
s
e
a
e
a
D
C
4
H
Q
L
c
c
a
3
Table 1. Inductor Examples
Boost Output Diode
Speed, forward voltage, and reverse current are very impor-
tant in selecting the output diode. In the boost configuration
the average diode current is the same as the average load
current and the peak is the same as the inductor and switch
current. The peak current is the same as the peak inductor
current and can be derived from Equation 3 or the graph in
Figure 13. Care must be taken to make sure that the peak
current is evaluated at the maximum input voltage.
The BAT54 and BAT85 series are low current Shottky diodes
available from
“
On Semiconductor
”
and
“
Phillips
”
respec-
tively. They are suitable for peak repetitive currents of 300mA
or less with good reverse current characteristics. For applica-
tions that are cost driven, the 1N4148 or equivalent will
provide sufficient switching speed with greater forward drop
and reduced cost. Other acceptable diodes are On
Semiconductor
’
s MBR0530 or Vishay
’
s B0530, although
they can have reverse currents that exceed 1 mA at very high
junction temperatures. Table 2 summarizes some typical
performance characteristics of various suitable diodes.
e
d
o
D
5
7
C
°
V
D
W
F
t
0
0
A
m
1
C
°
5
2
V
D
W
F
t
0
0
A
m
1
m
.
g
a
V
5
o
m
k
1
o
e
a
R
T
e
t
e
L
C
a
5
°
5
a
7
e
t
e
g
V
k
1
L
e
g
a
k
c
a
P
0
3
5
0
R
B
M
V
5
7
2
V
5
2
3
A
μ
5
A
μ
0
9
3
2
1
T
e
M
S
D
M
d
a
d
O
S
S
8
4
1
4
N
1
V
C
°
V
C
°
4
C
°
6
7
1
4
8
5
8
)
5
V
5
9
A
V
A
n
V
5
n
5
2
2
1
2
)
0
A
)
μ
V
A
V
A
5
°
2
2
1
2
2
8
0
μ
0
μ
d
e
n
a
T
4
5
T
A
B
)
5
V
5
4
0
)
)
T
M
S
5
8
T
A
B
)
5
V
6
5
A
μ
4
)
C
4
d
3
d
O
a
D
e
e
Table 2. Diode Examples
Output Capacitor
Due to the limited availability of tantalum capacitors, ceramic
capacitors and inexpensive electrolyics may be preferred.
Selection of the capacitor value will depend upon the peak
inductor current and inductor size. MuRata offers the GRM
series with up to 10uF @ 25V with a Y5V temperature
coefficient in a 1210 surface mount package. Low cost
applications can use the M series leaded electrolytic capaci-
tor from Panasonic. In general, ceramic, electrolytic, or
tantalum values ranging from 1
μ
F to 22
μ
F can be used for the
output capacitor.
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相關(guān)代理商/技術(shù)參數(shù) |
參數(shù)描述 |
|---|---|
| MIC2142BM5 EV | 制造商:Micrel Inc 功能描述: |
| MIC2142BM5 TR | 功能描述:IC REG BOOST FLYBK SEPIC SOT23-5 RoHS:否 類別:集成電路 (IC) >> PMIC - 穩(wěn)壓器 - DC DC 開關(guān)穩(wěn)壓器 系列:- 標準包裝:20 系列:SIMPLE SWITCHER® 類型:降壓（降壓） 輸出類型:固定 輸出數(shù):1 輸出電壓:12V 輸入電壓:4 V ~ 60 V PWM 型:電壓模式 頻率 - 開關(guān):52kHz 電流 - 輸出:1A 同步整流器:無 工作溫度:-40°C ~ 125°C 安裝類型:通孔 封裝/外殼:16-DIP（0.300"，7.62mm） 包裝:管件 供應(yīng)商設(shè)備封裝:16-DIP 其它名稱:*LM2575HVN-12LM2575HVN-12 |
| MIC2142BM5TR | 制造商:Rochester Electronics LLC 功能描述:- Tape and Reel |
| MIC2142YM5 | 制造商:Rochester Electronics LLC 功能描述: 制造商:Micrel Inc 功能描述: 制造商:RF Micro Devices Inc 功能描述: |
| MIC2142YM5 TR | 功能描述:直流/直流開關(guān)轉(zhuǎn)換器 Micropower SOT23-5 Boost Converter (Lead Free) RoHS:否 制造商:STMicroelectronics 最大輸入電壓:4.5 V 開關(guān)頻率:1.5 MHz 輸出電壓:4.6 V 輸出電流:250 mA 輸出端數(shù)量:2 最大工作溫度:+ 85 C 安裝風格:SMD/SMT |
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