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參數(shù)資料
| 型號(hào)： | ML4854 |
| 廠商： | Fairchild Semiconductor Corporation |
| 英文描述： | Adjustable, Low-Current, 2-Cell Boost Regulator with Shutdown and Low Battery Detect |
| 中文描述： | 可調(diào)，低電流，2節(jié)電池升壓關(guān)機(jī)和低電池檢測(cè)穩(wěn)壓器 |
| 文件頁(yè)數(shù)： | 8/13頁(yè) |
| 文件大?。?/td> | 133K |
| 代理商： | ML4854 |
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PRODUCT SPECIFICATION
ML4854
8
REV. 1.0.7 5/6/03
Block Diagram
Functional Description
Boost regulator
ML4854 is an adjustable boost regulator that combines vari-
able ON and minimum OFF architecture with synchronous
rectification. Unique control circuitry provides high-effi-
ciency power conversion for both light and heavy loads by
transitioning between discontinuous and continuous conduc-
tion based on load conditions. There is no oscillator; a con-
stant-peak-current limit of 1.5A in the switch allows the
inductor current to vary between this peak limit and some
lesser value. The switching frequency depends upon the load
and the input voltage, and can range up to 650kHz.
The input voltage (V
external Inductor to the V
L
pin of the device. The loop from
V
OUT
closes through the external resistive voltage divider to
the feedback pin V
FB
. The transfer ratio of this divider deter-
mines the output voltage. When V
FB
voltage drops below
V
REF
=1.23V, the error amplifier A1 signals to the regulator
to deliver a charge to the output by triggering the Variable
On-Time One Shot. This generates a pulse at the gate of the
Power NMOS transistor Q1. This transistor will charge the
Inductor L1 for the time interval (T
ON
) resulting in a peak
current given by:
IN
) comes to V
IN
pin and through the
When the one shot times out, the Q1 transistor releases the
V
L
pin, allowing the inductor to fly-back and momentary
charge the output through the body diode of the transistor
Q2. But, as the voltage across the Q2 changes polarity, its
gate will be driven low by the Synchronous Rectifier Control
Circuit (SRC), causing Q2 to short out its body diode. The
inductor then delivers the charge to the load by discharging
into it through Q2.
Under lightly loaded conditions, the amount of energy
delivered in this single pulse satisfies the voltage-control
loop, and the converter does not command any more energy
pulses until the output again drops below the lower-voltage
threshold. Under medium and heavy loads, a single energy
pulse is not sufficient to force the output voltage above its
upper threshold before the minimum off time has expired
and a second charge cycle is commanded. Since the inductor
current has not reached zero in this case, the peak current is
greater than the previous value at the end of the second
cycle. The result is a ratcheting of inductor current until
either the output voltage is satisfied, or the converter reaches
its set current limit.
After a period of time T
OFF
> 0.5μS, determined by Mini-
mum Off–Time Logic and if V
OUT
is low (V
FB
<V
REF
), the
Variable On-Time One Shot will be turned ON again and the
process repeats.
The output capacitor of the converter (see Test circuit) filters
the variable component, limiting the output voltage ripple to
a value determined by its capacitance and its ESR.
LBO
SHDN
Start-Up
Minimum
Off-Time
Logic
Variable
On-Time
One Shot
Current
Limit
Control
Synchronous
Rectifier
Control
4
7
2
6
5
8
3
1
V
IN
V
L
V
OUT
I
LIMIT
I
LIMIT
V
REF
V
OUT
GND
V
FB
I
LIMIT
SHDN
N
1
LBI
Q
1
Q
2
0.39V
A3
Control
Logic
A2
A1
–
+
–
+
–
+
SHDN
I
L PEAK
)
T
--------------------------
V
×
L
1
=
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|---|---|
| ML4854IT | 制造商:Rochester Electronics LLC 功能描述:- Bulk |
| ML4854ITX | 制造商:Rochester Electronics LLC 功能描述:- Bulk |
| ML485-G | 功能描述:射頻混合器 1.6-3.2 GHz High IP3 Mixer w/ Int LO Amp RoHS:否 制造商:NXP Semiconductors 頻率范圍: 轉(zhuǎn)換損失——最大: 工作電源電壓:6 V 最大工作溫度:+ 85 C 最小工作溫度:- 40 C 安裝風(fēng)格:Through Hole 封裝 / 箱體:PDIP-8 封裝:Tube |
| ML485-PCB | 功能描述:射頻開發(fā)工具 ML485 1.6-3.2GHz Eval Brd Active Mxr RoHS:否 制造商:Taiyo Yuden 產(chǎn)品:Wireless Modules 類型:Wireless Audio 工具用于評(píng)估:WYSAAVDX7 頻率: 工作電源電壓:3.4 V to 5.5 V |
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