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參數(shù)資料
| 型號： | MAX1802 |
| 廠商： | Maxim Integrated Products, Inc. |
| 英文描述： | Digital Camera Step-Down Power Supply |
| 中文描述： | 數(shù)碼相機(jī)降壓型電源 |
| 文件頁數(shù)： | 26/28頁 |
| 文件大?。?/td> | 469K |
| 代理商： | MAX1802 |
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M
Digital Camera Step-Down
Power Supply
26
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converter is the SEPIC, shown in Figure 9. Inductors L1
and L2 can be separate inductors or can be wound on
a single core and coupled like a transformer. Typically,
using a coupled inductor will improve efficiency since
some power is transferred through the coupling, so less
power passes through the coupling capacitor (C2).
Likewise, C2 should have low ESR to improve efficien-
cy. The ripple current rating must be greater than the
larger of the input and output currents. The MOSFET
(Q1) drain-source voltage rating and the rectifier (D1)
reverse-voltage rating must exceed the sum of the
input and output voltages. Other types of step-up/step-
down circuits are a flyback converter and a step-up
converter followed by a linear regulator.
Using an Auxiliary Controller for a
Multi-Output Flyback Circuit
Some applications require multiple voltages from a sin-
gle converter that features a flyback transformer.
Figure 10 shows a MAX1802 auxiliary controller in a
two-output flyback configuration. The controller drives
an external MOSFET that switches the transformer pri-
mary, and the two secondaries generate the outputs.
Only a single positive output voltage can be regulated
using the feedback resistive voltage-divider, so the
other voltages are set by the turns ratio of the trans-
former secondaries. The regulation of the other sec-
ondary voltages degrades due to transformer leakage
inductance and winding resistance. Voltage regulation
is best when the load current is limited to a small range.
Consult the transformer manufacturer for the proper
design for a given application.
Using a Charge Pump for Negative
Output Voltages
Negative output voltages can be produced without a
transformer using a charge-pump circuit with an auxil-
iary controller as shown in Figure 11. When MOSFET
Q1 turns off, the voltage at its drain rises to supply cur-
rent to V
OUT+
. At the same time, C1 charges to the volt-
age at V
OUT+
through D1. When the MOSFET turns on,
C1 discharges through D3, thereby charging C3 to
V
OUT-
minus the drop across D3 to create roughly the
same voltage as V
OUT+
at V
OUT-
but with inverted
polarity. If different magnitudes are required for the
positive and negative voltages, a linear regulator can
be used at one of the outputs to achieve the desired
voltage.
Designing a PC Board
A good PC board layout is important to achieve optimal
performance from the MAX1802. Good design reduces
excessive conducted and/or radiated noise, both of
which are undesirable.
Conductors carrying discontinuous currents should be
kept as short as possible. Conductors carrying high
currents should be made as wide as possible. A sepa-
rate low-noise ground plane containing the reference
and signal grounds should only connect to the power-
ground plane at one point to minimize the effects of
power-ground currents.
Keep the voltage feedback network very close to the
IC, preferably within 0.2in (5mm) of the FB_ pin. Nodes
with high dv/dt (switching nodes) should be kept as
small as possible and should stay away from high-
impedance nodes such as FB_ and COMP_.
Refer to the MAX1802EVKIT evaluation kit manual for a
full PC board example.
Chip Information
TRANSISTOR COUNT: 7740
R
C
G
C
MAX1802
D1
L2
L1
C2
Q1
R1
OUTPUT
3.3V
R2
INPUT
1 CELL
Li+
MAIN
ON
COMP
DCON
EXT
FB
Figure 9. Auxiliary Controller, SEPIC Configuration
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| MAX1802EHJ | 功能描述:直流/直流開關(guān)轉(zhuǎn)換器 Step-Up Slave DC/DC Controller 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 |
| MAX1802EHJ+ | 功能描述:直流/直流開關(guān)轉(zhuǎn)換器 Step-Up Slave DC/DC Controller 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 |
| MAX1802EHJ+T | 功能描述:直流/直流開關(guān)轉(zhuǎn)換器 Step-Up Slave DC/DC Controller 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 |
| MAX1802EHJ-T | 功能描述:直流/直流開關(guān)轉(zhuǎn)換器 Step-Up Slave DC/DC Controller 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 |
| MAX1804EUB | 功能描述:電流和電力監(jiān)控器、調(diào)節(jié)器 RoHS:否 制造商:STMicroelectronics 產(chǎn)品:Current Regulators 電源電壓-最大:48 V 電源電壓-最小:5.5 V 工作溫度范圍:- 40 C to + 150 C 安裝風(fēng)格:SMD/SMT 封裝 / 箱體:HPSO-8 封裝:Reel |
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