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參數(shù)資料
| 型號(hào)： | ML4865 |
| 廠商： | Fairchild Semiconductor Corporation |
| 英文描述： | High Voltage High Current Boost Regulator |
| 中文描述： | 高電壓大電流升壓穩(wěn)壓器 |
| 文件頁(yè)數(shù)： | 5/10頁(yè) |
| 文件大小： | 126K |
| 代理商： | ML4865 |
PRODUCT SPECIFICATION
ML4865
REV. 1.0.2 8/10/01
5
Functional Description
The ML4865 combines a unique form of current mode con-
trol with a synchronous rectifier to create a boost converter
that can deliver high currents while maintaining high effi-
ciency. Current mode control allows the use of a very small,
high frequency inductor and output capacitor. Synchronous
rectification replaces the conventional external Schottky
diode with an on-chip PMOS FET to reduce losses, eliminate
an external component, and allows for load disconnect. Also
included on-chip are an NMOS switch and current sense
resistor, further reducing the number of external components,
which makes the ML4865 very easy to use.
Regulator Operation
The ML4865 is a variable frequency, current mode switching
regulator. Its unique control scheme converts efficiently over
more than three decades of load current. A detailed block
diagram of the boost converter is shown in Figure 2.
Error amplifier A3 converts deviations in the desired output
voltage to a small current, I
SET
. The inductor current is mea-
sured through a 150m
resistor which is amplified by A1.
The boost control block matches the average inductor current
to a multiple of the I
SET
current by switching Q1 on and off.
The peak inductor current is limited by the controller to
about 1.2A.
At light loads, I
SET
will momentarily reach zero after an
inductor discharge cycle causing Q1 to stop switching.
Depending on the load, this idle time can extend to tenths of
seconds. While the circuit is not switching, only 25μA of
supply current is drawn from the output. This allows the part
to remain efficient even when the load current drops below
250μA.
Amplifier A2 and the PMOS transistor Q2 work together to
form a low drop diode. When transistor Q1 turns off, the cur-
rent flowing in the inductor causes pin 6 to go high. As the
voltage on V
L2
rises above V
OUT
, amplifier A2 allows the
PMOS transistor Q2 to turn on. In discontinuous operation,
(where I
L
always returns to zero), A2 uses the resistive drop
across the PMOS switch Q2 to sense zero inductor current
and turns the PMOS switch off. In continuous operation, the
PMOS turn off is independent of A2 and is determined by the
boost control circuitry.
Typical inductor current and voltage waveforms are shown in
Figure 3.
Shutdown
The SHDN pin should be held low for normal operation.
Raising the shutdown voltage above the threshold level will
disable the synchronous rectifier, Q2 and Q3, and force I
SET
to zero. This prevents switching from occurring and
disconnects the body diode of Q2 from the output. As a
result, the output voltage is allowed to drop below the input
voltage and current is prevented from flowing from the input
to the output.
Feedback
The SENSE pin should be left open or bypassed to ground
for normal operation. The addition of the resistor divider R1
and R2 causes the input of error amplifier A3 to reach the
threshold voltage before the internal resistors do. This
allows the ML4865 to provide output voltages lower than the
preset 12V if desired.
Design Considerations
Input Voltage Range
The input voltage range determines whether an external
Schottky diode is necessary or optional. If the input voltage
is 6V or lower, the ML4865 can be operated as a stand alone
boost regulator with a shutdown that fully isolates the input
from the output. Adding an optional Schottky diode extends
the input voltage range up to 10V, and improves the effi-
ciency and the output current capability. However, the exter-
nal diode now provides a leakage path from the input to the
output during shutdown.
Output Current Capability
The maximum current available at the output of the regulator
is related to the maximum inductor current by the ratio of the
input to output voltage and the full load efficiency. The max-
imum inductor current is dependent on the input voltage.
The full load efficiency may be as low as 65% when the
ML4865 is used without a Schottky diode and can exhibit an
input voltage dependence when an external diode is used.
The maximum output current can be determined by using the
typical performance curves shown in Figures 4 and 5, or by
calculation using the following empirical equation:
Where, for applications using the internal synchronous
rectifier:
And for applications using an external Schottky:
I
V
V
I
OUT MAX
(
IN
OUT
IN
)
×
× η
(A)
(1)
I
V
(
(
(
(
V
V
OUT MAX
(
IN
OUT
IN
)
.
.
.
×
×
+
×
005
0 4
065
I
V
IN
IN
=
×
+
005
.
(
0 4
.
η =
065
.
(
I
V
V
V
V
OUT MAX
(
IN
OUT
IN
IN
)
.
.
.
.
×
×
+
×
×
+
007
0 4
0025
065
(
(
(
(
(
(
(
(
(
(
(
(
I
V
IN
IN
=
×
+
007
.
0 4
.
η =
×
+
0025
.
065
.
V
IN
相關(guān)PDF資料 |
PDF描述 |
|---|---|
| ML4866 | 3.3V Output DC-DC Step-Down Converter(3.3V輸出的DC-DC步降變換器) |
| ML4869 | Medium Current Boost Regulator with Load Disconnect(負(fù)載可分離的中等電流升壓穩(wěn)壓器) |
| ML4870 | High Current Boost Regulator with Load Disconnect(負(fù)載可分離的大電流升壓穩(wěn)壓器) |
| ML4872 | High Current Boost Regulator with Shutdown(帶關(guān)斷電路的大電流升壓穩(wěn)壓器) |
| ML4875 | High Current Boost Regulator with Shutdown(帶關(guān)斷電路的大電流升壓穩(wěn)壓器) |
相關(guān)代理商/技術(shù)參數(shù) |
參數(shù)描述 |
|---|---|
| ML4865CS2 | 功能描述:開(kāi)關(guān)變換器、穩(wěn)壓器與控制器 SOIC-8 RoHS:否 制造商:Texas Instruments 輸出電壓:1.2 V to 10 V 輸出電流:300 mA 輸出功率: 輸入電壓:3 V to 17 V 開(kāi)關(guān)頻率:1 MHz 工作溫度范圍: 安裝風(fēng)格:SMD/SMT 封裝 / 箱體:WSON-8 封裝:Reel |
| ML4865CS-2 | 制造商:MICRO-LINEAR 制造商全稱(chēng):MICRO-LINEAR 功能描述:High Voltage High Current Boost Regulator |
| ML4865CS2X | 功能描述:DC/DC 開(kāi)關(guān)控制器 SOIC-8 RoHS:否 制造商:Texas Instruments 輸入電壓:6 V to 100 V 開(kāi)關(guān)頻率: 輸出電壓:1.215 V to 80 V 輸出電流:3.5 A 輸出端數(shù)量:1 最大工作溫度:+ 125 C 安裝風(fēng)格: 封裝 / 箱體:CPAK |
| ML4865ES-2 | 制造商:MICRO-LINEAR 制造商全稱(chēng):MICRO-LINEAR 功能描述:High Voltage High Current Boost Regulator |
| ML4866 | 制造商:MICRO-LINEAR 制造商全稱(chēng):MICRO-LINEAR 功能描述:3.3V Output DC-DC Step-Down Converter |
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