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參數(shù)資料
| 型號： | MAX1748EUE |
| 廠商： | MAXIM INTEGRATED PRODUCTS INC |
| 元件分類： | 穩(wěn)壓器 |
| 英文描述： | Triple-Output TFT LCD DC-DC Converter |
| 中文描述： | 2 A SWITCHING REGULATOR, 1250 kHz SWITCHING FREQ-MAX, PDSO16 |
| 封裝： | 4.40 MM, 1.10 MM HEIGHT, 0.65 MM PITCH, MO-153-AB, TSSOP-16 |
| 文件頁數(shù)： | 11/16頁 |
| 文件大?。?/td> | 277K |
| 代理商： | MAX1748EUE |
M
Triple-Output TFT LCD DC-DC Converter
______________________________________________________________________________________
11
converter reaches regulation, the negative charge
pump turns on. When the negative output voltage
reaches approximately 88% of its nominal value (V
FBN
< 110mV), the positive charge pump starts up. Finally,
when the positive output voltage reaches 90% of its
nominal value (V
FBP
> 1.125V), the active-low ready
signal (
RDY
) goes low (see
Power Ready
section).
Power Ready
Power ready is an open-drain output. When the power-
up sequence is properly completed, the MOSFET turns
on and pulls
RDY
low with a typical 125
on-resis-
tance. If a fault is detected, the internal open-drain
MOSFET appears as a high impedance. Connect a
100k
pull-up resistor between
RDY
and IN for a logic-
level output.
Fault Detection
Once
RDY
is low and if any output falls below its fault-
detection threshold,
RDY
goes high impedance.
For the reference, the fault threshold is 1.05V. For the
main boost converter, the fault threshold is 88% of its
nominal value (V
FB
< 1.1V). For the negative charge
pump, the fault threshold is approximately 90% of its
nominal value (V
FBN
< 130mV). For the positive charge
pump, the fault threshold is 88% of its nominal value
(V
FBP
< 1.11V).
Once an output faults, all outputs later in the power
sequence shut down until the faulted output rises
above its power-up threshold. For example, if the nega-
tive charge-pump output voltage falls below the fault
detection threshold, the main boost converter remains
active while the positive charge pump stops switching
and its output voltage decays, depending on output
capacitance and load. The positive charge-pump out-
put will not power up until the negative charge-pump
output voltage rises above its power-up threshold (see
the
Power-Up Sequencing
section).
Voltage Reference
The voltage at REF is nominally 1.25V. The reference
can source up to 50μA with good load regulation (see
Typical Operating Characteristics
). Connect a 0.22μF
bypass capacitor between REF and GND.
Design Procedure
Main Boost Converter
Output Voltage Selection
Adjust the output voltage by connecting a voltage
divider from the output (V
MAIN
) to FB to GND (see
Typical Operating Circuit
). Select R2 in the 10k
to
20k
range. Higher resistor values improve efficiency
at low output current but increase output voltage error
due to the feedback input bias current. Calculate R1
with the following equations:
R1 = R2 [(V
MAIN
/ V
REF
) - 1]
where V
REF
= 1.25V. V
MAIN
may range from V
IN
to 13V.
Feedback Compensation
For stability, add a pole-zero pair from FB to GND in the
form of a series resistor (R
COMP
) and capacitor
(C
COMP
). The resistor should be half the value of the
R2 feedback resistor.
Inductor Selection
Inductor selection depends on input voltage, output
voltage, maximum current, switching frequency, size,
and availability of inductor values. Other factors can
include efficiency and ripple voltage. Inductors are
specified by their inductance (L), peak current (I
PEAK
),
and resistance (R
L
). The following boost-circuit equa-
tions are useful in choosing inductor values based on
the application. They allow the trading of peak current
and inductor value while allowing for consideration of
component availability and cost.
The following equation includes a constant LIR, which
is the ratio of the inductor peak-to-peak AC current to
maximum average DC inductor current. A good com-
promise between the size of the inductor, loss, and out-
put ripple is to choose an LIR of 0.3 to 0.5. The peak
inductor current is then given by:
The inductance value is then given by:
2
=
Considering the typical application circuit, the maxi-
mum DC load current (I
MAIN(MAX)
) is 200mA with a 10V
output. A 6.8μH inductance value is then chosen,
based on the above equations and using 85% efficien-
cy and a 1MHz operating frequency. Smaller induc-
tance values typically offer a smaller physical size for a
given series resistance and current rating, allowing the
smallest overall circuit dimensions. However, due to
higher peak inductor currents, the output voltage ripple
(I
PEAK
output filter capacitor ESR) will be higher.
Use inductors with a ferrite core or equivalent; powder
iron cores are not recommended for use with the
MAX1748
’
s high switching frequencies. The inductor
’
s
maximum current rating should exceed I
PEAK
. Under
fault conditions, inductor current may reach up to 2.0A.
L
V
Efficiency
(V
V
)
V
LIR
I
f
IN(MIN)
MAIN
IN(MIN)
(MAIN)
2
MAIN(MAX)
OSC
×
×
×
×
×
I
I
V
Efficiency
V
1
[
(LIR/2)
PEAK
MAIN(MAX)
MAIN
IN(MIN)
=
×
×
×
+
]
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|---|---|
| MAX1748EUE+ | 功能描述:直流/直流開關(guān)轉(zhuǎn)換器 Triple-Output TFT LCD DC/DC Converters 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(fēng)格:SMD/SMT |
| MAX1748EUE+T | 功能描述:直流/直流開關(guān)轉(zhuǎn)換器 Triple-Output TFT LCD DC/DC Converters 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(fēng)格:SMD/SMT |
| MAX1748EUE-T | 功能描述:直流/直流開關(guān)轉(zhuǎn)換器 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(fēng)格:SMD/SMT |
| MAX1748EUE-TG069 | 制造商:Rochester Electronics LLC 功能描述: 制造商:Maxim Integrated Products 功能描述: |
| MAX1748EVKIT | 功能描述:電源管理IC開發(fā)工具 MAX1748 Eval Kit RoHS:否 制造商:Maxim Integrated 產(chǎn)品:Evaluation Kits 類型:Battery Management 工具用于評估:MAX17710GB 輸入電壓: 輸出電壓:1.8 V |
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