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參數(shù)資料
| 型號： | MIC4721 |
| 廠商： | Micrel Semiconductor,Inc. |
| 英文描述： | Quad UART with 16-byte FIFO and infrared (IrDA) encoder/decoder, SOT315-1 (LQFP80), Reel Dry Pack, SMD, 13",Turned |
| 中文描述： | 1.5A的2MHz的集成開關(guān)降壓穩(wěn)壓器 |
| 文件頁數(shù)： | 12/19頁 |
| 文件大小： | 827K |
| 代理商： | MIC4721 |
Micrel, Inc.
MIC4721
Output Capacitor
The MIC4721 is designed for a 4.7μF output capacitor.
X5R or X7R dielectrics are recommended for the output
capacitor. Y5V dielectrics lose most of their capacitance
over temperature and voltage and are therefore, not
recommended. Smaller case size capacitors are
recommended due to their lower ESL. The MIC4721
utilizes type III voltage mode internal compensation and
utilizes an internal zero to compensate for the double
pole roll off of the LC filter. For this reason, larger output
capacitors can create instabilities. In cases where a
4.7μF output capacitor is not sufficient, the MIC2208
offers the ability to externally control the compensation,
allowing for a wide range of output capacitor types and
values.
May 2007
12
M9999-052907-A
Inductor Selection
The MIC4721 is designed for use with a 1μH inductor.
Proper selection should ensure the inductor can handle
the maximum RMS and peak currents required by the
load. Maximum current ratings of the inductor are
generally given in two methods; permissible DC current
and saturation current. Permissible DC current can be
rated either for a 40°C temperature rise or a 10% to 20%
loss in inductance. Ensure the inductor selected can
handle the maximum operating current. When saturation
current is specified, make sure that there is enough
margin that the peak current since at higher
temperatures, the inductor will saturate at a lower
current.
Diode Selection
Since the MIC4721 is non-synchronous, a free-wheeling
diode is required for proper operation. A Schottky diode
is recommended due to the low forward voltage drop
and fast reverse recovery time. The diode should be
rated to handle the average output current. Also, the
reverse voltage rating of the diode should exceed the
maximum input voltage. Please refer to the layout
recommendations to minimize switching noise.
Feedback Resistors
The feedback resistor set the output voltage by dividing
down the output and sending it to the feedback pin. The
feedback voltage is 1.0V. Calculating the set output
voltage is as follows:
+
=
1
2
1
R
R
V
V
FB
OUT
Where R1 is the resistor from V
OUT
to FB and R2 is the
resistor from FB to GND.
The recommended feedback resistor values for common
output voltages are available in the bill of materials at the
end of this specification. Although the resistance range
of the FB resistors is very wide, R1 is recommended to
be 10K. This minimizes the effect the parasitic
capacitance of the FB node. Resistor R2 can be
calculated by:
FB
OUT
V
FB
V
V
R
R
×
=
1
2
Feedforward Capacitor (C
FF
)
A capacitor across the resistor from the output to the
feedback pin (R1) is recommended for most designs.
This capacitor can give a boost to phase margin and
increase the bandwidth for transient response. Also,
large values of feedforward capacitance can slow down
the turn-on characteristics, reducing inrush current. For
maximum phase boost, C
FF
can be calculated as follows:
1
KHz
×
π
1
200
2
R
C
FF
×
=
Bias filter
A small 10
resistor is recommended from the input
supply to the bias pin along with a small 0.1μF ceramic
capacitor from bias-to-ground. This will bypass the high
frequency noise generated by the violent switching of
high currents from reaching the internal reference and
control circuitry. Tantalum and electrolytic capacitors are
not recommended since these types of capacitors aren’t
as effective at filtering high frequencies.
Loop Stability and Bode Analysis
Bode analysis is an excellent way to measure small
signal stability and loop response in power supply
designs. Bode analysis monitors gain and phase of a
control loop. This is done by breaking the feedback loop
and injecting a signal into the feedback node and
comparing the injected signal to the output signal of the
control loop. This will require a network analyzer to
sweep the frequency and compare the injected signal to
the output signal. The most common method of injection
is the use of a transformer. Figure 7 demonstrates how a
transformer is used to inject a signal into the feedback
network.
Figure 7. Transformer Injection
A 50
resistor allows impedance matching from the
network analyzer source. This method allows the DC
loop to maintain regulation and allow the network
analyzer to insert an AC signal on top of the DC voltage.
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相關(guān)代理商/技術(shù)參數(shù) |
參數(shù)描述 |
|---|---|
| MIC4721YMM | 功能描述:直流/直流開關(guān)調(diào)節(jié)器 1.5A 2MHz Buck Regulator RoHS:否 制造商:International Rectifier 最大輸入電壓:21 V 開關(guān)頻率:1.5 MHz 輸出電壓:0.5 V to 0.86 V 輸出電流:4 A 輸出端數(shù)量: 最大工作溫度: 安裝風(fēng)格:SMD/SMT 封裝 / 箱體:PQFN 4 x 5 |
| MIC4721YMM TR | 功能描述:直流/直流開關(guān)調(diào)節(jié)器 1.5A 2MHz Buck Regulator RoHS:否 制造商:International Rectifier 最大輸入電壓:21 V 開關(guān)頻率:1.5 MHz 輸出電壓:0.5 V to 0.86 V 輸出電流:4 A 輸出端數(shù)量: 最大工作溫度: 安裝風(fēng)格:SMD/SMT 封裝 / 箱體:PQFN 4 x 5 |
| MIC4721YMMTR | 功能描述:IC REG BUCK ADJ 1.5A 10MSOP RoHS:是 類別:集成電路 (IC) >> PMIC - 穩(wěn)壓器 - DC DC 開關(guān)穩(wěn)壓器 系列:- 標(biāo)準(zhǔn)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 |
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| MIC4722_10 | 制造商:MICREL 制造商全稱:Micrel Semiconductor 功能描述:3mm x 3mm 2.7MHz 3A PWM Buck Regulator |
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