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參數(shù)資料
| 型號： | MAX1678 |
| 廠商： | Maxim Integrated Products, Inc. |
| 元件分類： | DC/DC變換器 |
| 英文描述： | 1-Cell to 2-Cell, Low-Noise, High-Efficiency, Step-Up DC-DC Converter |
| 中文描述： | 1節(jié)至2節(jié)電池、低噪聲、高效率、升壓型DC-DC轉(zhuǎn)換器 |
| 文件頁數(shù)： | 9/12頁 |
| 文件大小： | 166K |
| 代理商： | MAX1678 |
S hutdown Mode
Pulling the
SHDN
pin low places the MAX1678 in shut-
down mode (I
SHDN
= 2μA typical). In shutdown, the
internal switching MOSFET turns off, PFO goes high
impedance, and the synchronous rectifier turns off to
prevent the flow of reverse current from the output back
to the input. However, there is still a forward current
path through the synchronous-rectifier body diode from
the input to the output. Thus, in shutdown, the output
remains one diode drop below the battery voltage
(V
BATT
).
To disable the shutdown feature, connect
SHDN
(a
logic input) to BATT or OUT.
Reverse-Battery Protec tion
The MAX1678 can sustain/survive battery reversal up to
the package power-dissipation limit. An internal 5
resistor in series with a diode limits reverse current to
less than 220mA, preventing damage. Prolonged oper-
ation above 220mA reverse-battery current can
degrade the device’s performance.
Power-Fail Comparator
The MAX1678 has an on-chip comparator for power-fail
detection. This comparator can detect a loss of power
at the input or output (Figures 7 and 8). If the voltage at
the power-fail input (PFI) falls below 614mV, the PFO
output sinks current to GND. Hysteresis at PFI is 2%.
The power-fail monitor threshold is set by two resistors,
R3 and R4, using the following equation:
where V
TH
is the desired threshold of the power-fail
detector, and V
PFI
is the 614mV threshold of the power-
fail comparator. Since PFI leakage is 10nA max, select
feedback resistor R4 in the 100k
to 1M
range.
Damping S witc h
The MAX1678 is designed with an internal damping
switch to minimize ringing at the LX node. The damping
switch (Figure 4) connects the LX node to BATT, effec-
tively depleting the inductor’s remaining energy. When
the energy in the inductor is insufficient to supply cur-
rent to the output, the capacitance and inductance at
LX form a resonant circuit that causes ringing. The
damping switch supplies a path to quickly dissipate
this energy, suppressing the ringing at LX. This does
not reduce the output ripple, but does reduce EMI.
Figures 5 and 6 show the LX node voltage waveform
without and with the damping switch.
R3 = R4 x
V
V
TH
PFI
1
M
1-Cell to 2-Cell, Low-Noise,
High-Effic ienc y, S tep-Up DC-DC Converter
_______________________________________________________________________________________
9
MAX1678
PDRV
DAMP
NDRV
TIMING
CIRCUIT
OUT
V
OUT
V
IN
BATT
LX
DAMPING
SWITCH
GND
P
P
N
Figure 4. Simplified Diagram of Damping Switch
2
μ
s/div
1
V
BATT
= 2.5V
V
OUT
= 3.3V
L1 = 47
μ
H
Figure 5. LX Ringing Without Damping Switch (example only)
2
μ
s/div
1
V
BATT
= 1.8V
V
OUT
= 3.3V
L1 = 47
μ
H
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相關(guān)代理商/技術(shù)參數(shù) |
參數(shù)描述 |
|---|---|
| MAX1678ESA | 制造商:Rochester Electronics LLC 功能描述: 制造商:Maxim Integrated Products 功能描述: |
| MAX1678EUA | 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 |
| MAX1678EUA+ | 功能描述:直流/直流開關(guān)轉(zhuǎn)換器 1-2 Cell Step-Up DC/DC Converter 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 |
| MAX1678EUA+T | 功能描述:直流/直流開關(guān)轉(zhuǎn)換器 1-2 Cell Step-Up DC/DC Converter 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 |
| MAX1678EUAT | 制造商:Maxim Integrated Products 功能描述: |
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