- 您現(xiàn)在的位置：買賣IC網(wǎng) > PDF目錄359170 > ML4851CS-3 Low Current, Voltage Boost Regulator PDF資料下載
參數(shù)資料
| 型號： | ML4851CS-3 |
| 英文描述： | Low Current, Voltage Boost Regulator |
| 中文描述： | 低電流，電壓升壓穩(wěn)壓器 |
| 文件頁數(shù)： | 7/9頁 |
| 文件大小： | 286K |
| 代理商： | ML4851CS-3 |
7
ML4851
July 2000
DATASHEET
After the appropriate inductor value is chosen, it is
necessary to find the minimum inductor current rating
required. Peak inductor current is determined from the
following formula:
(3)
In the two cell application previously described, a
maximum input voltage of 3V would give a peak current
of 1A. When comparing various inductors, it is important
to keep in mind that suppliers use different criteria to
determine their ratings. Many use a conservative current
level, where inductance has dropped to 90% of its normal
level. In any case, it is a good idea to try inductors of
various current ratings with the ML4851 to determine
which inductor is the best choice. Check efficiency and
maximum output current, and if a current probe is
available, look at the inductor current to see if it looks
like the waveform shown in Figure 3. For additional
information, see Applications Note 29, “Choosing an
Inductor for Your ML4861 Application.”
Suitable inductors can be purchased from the following
suppliers:
Coilcraft
(847) 639-6400
Coiltronics
(561) 241-7876
Dale
(605) 665-9301
Sumida
(847) 956-0666
XFMRS, Inc. (317) 834-1066
OUTPUT CAPACITOR
The choice of output capacitor is also important, as it
controls the output ripple and optimizes the efficiency of
the circuit. Output ripple is influenced by three capacitor
parameters: capacitance, ESR, and ESL. The contribution
due to capacitance can be determined by looking at the
change in capacitor voltage required to store the energy
delivered by the inductor in a single charge-discharge
cycle, as determined by the following formula:
(4)
For a 2.4V input, and 5V output, a 18μH inductor, and a
47μF capacitor, the expected output ripple due to
capacitor value is 33mV.
Capacitor Equivalent Series Resistance (ESR) and
Equivalent Series Inductance (ESL), also contribute to the
output ripple due to the inductor discharge current
waveform. Just after the NMOS transistor turns off, the
output current ramps quickly to match the peak inductor
current. This fast change in current through the output
capacitor’s ESL causes a high frequency (5ns) spike that
can be over 1V in magnitude. After the ESL spike settles,
the output voltage still has a ripple component equal to
the inductor discharge current times the ESR. This
component will have a sawtooth shape and a peak value
equal to the peak inductor current times the ESR. ESR
also has a negative effect on efficiency by contributing
I
2
R losses during the discharge cycle.
An output capacitor with a capacitance of 100μF, an ESR
of less than 0.1
W
, and an ESL of less than 5nH is a good
general purpose choice. Tantalum capacitors which meet
these requirements can be obtained from the following
suppliers:
Matsuo
(207) 282-5111
Sprague
(207) 324-4140
If ESL spikes are causing output noise problems, an EMI
filter can be added in series with the output.
INPUT CAPACITOR
Unless the input source is a very low impedance battery,
it will be necessary to decouple the input with a
capacitor with a value of between 47μF and 100μF. This
provides the benefits of preventing input ripple from
affecting the ML4851 control circuitry, and it also
improves efficiency by reducing I
2
R losses during the
charge and discharge cycles of the inductor. Again, a low
ESR capacitor (such as tantalum) is recommended.
REFERENCE CAPACITOR
Under some circumstances input ripple cannot be reduced
effectively. This occurs primarily in applications where
inductor currents are high, causing excess output ripple
due to “pulse grouping”, where the charge-discharge
pulses are not evenly spaced in time. In such cases it may
be necessary to decouple the reference pin (V
REF
) with a
small 10nF to 100nF ceramic capacitor. This is
particularly true if the ripple voltage at V
IN
is greater than
100mV.
SETTING THE
RESET
THRESHOLD
To use the
RESET
comparator as an input voltage monitor,
as shown in Figure 1, it is necessary to use an external
resistor divider tied to the DETECT pin as shown in the
block diagram. The resistor values R
A
and R
B
can be
calculated using the following equation:
02
1
(5)
The value of R
B
should be 100k
W
or less to minimize bias
current errors. R
A
is then found by rearranging the
equation:
DESIGN CONSIDERATIONS
(Continued)
V
R
IN MIN
(
B
)
A
B
.
R
R
=
×
+
6
V
t
V
L
C
V
V
OUT
ON
IN
OUT
IN
=
×
1
× ×
×
2
2
2
6
I
t
V
L
L PEAK
(
ON MAX
(
IN MAX
(
MIN
)
)
)
=
×
相關(guān)PDF資料 |
PDF描述 |
|---|---|
| ML4861CS-3 | Low Voltage Boost Regulator |
| ML4861ES-6 | Low Voltage Boost Regulator |
| ML4869ES-3 | Medium Current Boost Regulator with Load Disconnect |
| ML4869ES-5 | Medium Current Boost Regulator with Load Disconnect |
| ML4870CS-3 | High Current Boost Regulator with Load Disconnect |
相關(guān)代理商/技術(shù)參數(shù) |
參數(shù)描述 |
|---|---|
| ML4851CS3X | 制造商:Rochester Electronics LLC 功能描述:- Bulk |
| ML4851CS3X_NL4C0095 | 制造商:Rochester Electronics LLC 功能描述:- Bulk |
| ML4851CS-5 | 制造商:MICRO-LINEAR 制造商全稱:MICRO-LINEAR 功能描述:Low Current, Voltage Boost Regulator |
| ML4851CS8-3 UP WAF | 制造商:Fairchild Semiconductor Corporation 功能描述: |
| ML4851CS8-5 UP WAF | 制造商:Fairchild Semiconductor Corporation 功能描述: |
發(fā)布緊急采購，3分鐘左右您將得到回復(fù)。