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參數資料
| 型號： | MAX1774EEI |
| 廠商： | MAXIM INTEGRATED PRODUCTS INC |
| 元件分類： | 穩(wěn)壓器 |
| 英文描述： | Dual, High-Efficiency, Step-Down Converter with Backup Battery Switchover |
| 中文描述： | 3 A SWITCHING CONTROLLER, 1250 kHz SWITCHING FREQ-MAX, PDSO28 |
| 封裝： | 0.150 INCH, 0.025 INCH PITCH, QSOP-28 |
| 文件頁數： | 13/21頁 |
| 文件大?。?/td> | 398K |
| 代理商： | MAX1774EEI |
M
Dual, High-Effic ienc y, S tep-Down
Converter with Bac kup Battery S witc hover
______________________________________________________________________________________
13
100% duty cycle fail. Dropout voltage is defined as the
difference between the input and output voltages when
the input is low enough for the output to drop out of
regulation. Dropout depends on the MOSFET drain-to-
source on-resistance, current-sense resistor, and
inductor series resistance, and is proportional to the
load current:
V
DROPOUT
= I
OUT
[R
DS(ON)
+ R
SENSE
+ R
L
]
Regulation Control S c heme
The MAX1774 has a unique operating scheme that
allows PWM operation at medium and high current,
automatically switching to pulse-skipping mode at
lower currents to improve light-load efficiency. Figure 2
shows a simplified block diagram.
Under medium and heavy load operation, the inductor
current is continuous and the part operates in PWM
mode. In this mode, depending on the duty cycle,
either the minimum on-time or the minimum off-time
sets the switching frequency. The duty cycle is approxi-
mately the output voltage divided by the input voltage.
If the duty cycle is less than 50%, the minimum on-time
controls the frequency, and the frequency is approxi-
mately f
≈
2.5MHz
D, where D is the duty cycle. If the
duty cycle is greater than 50%, the minimum off-time
sets the frequency, and the frequency is approximately
f
≈
2.5MHz
(1 - D).
In both cases, the error comparator regulates the volt-
age. For low duty cycles (<50%), the P-channel MOS-
FET is turned on for the minimum on-time, causing
fixed-on-time operation. During the MOSFET on-time,
the output voltage rises. Once the MOSFET is turned
off, the voltage drops to the regulation threshold, when
another cycle is initiated. For high duty cycles (>50%),
the MOSFET remains off for the minimum off-time,
causing fixed-off-time operation. In this case, the MOS-
FET remains on until the output voltage rises to the reg-
ulation threshold. Then the MOSFET turns off for the
minimum off-time, initiating another cycle.
By switching between fixed-on-time and fixed-off-time
operation, the MAX1774 can operate at high input-out-
put ratios and still operate up to 100% duty cycle for
low dropout. When operating from fixed-on-time opera-
tion, the minimum output voltage is regulated, but in
fixed-off-time operation, the maximum output voltage is
regulated. Thus, as the input voltage drops below
approximately twice the output voltage, a decrease in
line regulation can be expected. The drop in voltage is
approximately V
DROP
≈
V
RIPPLE.
At light output loads,
the inductor current is discontinuous, causing the
MAX1774 to operate at lower frequencies, reducing the
MOSFET gate drive and switching losses. In discontin-
uous mode, under most circumstances, the on-time will
be a fixed minimum on-time of 400ns.
PSW
NON
PON
V
O
NSW
NONOVERLAP
PROTECTION
Q
S
R
S
R
Q
TONMIN
TOFFMIN
V
CLM
V
ZERO
FB
REF
CS+
CS-
V
VALLEY
V
MIN
V
IN
PON
Figure 2. Simplified Control System Block Diagram
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相關代理商/技術參數 |
參數描述 |
|---|---|
| MAX1774EEI+ | 功能描述:直流/直流開關轉換器 Dual Step-Down w/Switchover RoHS:否 制造商:STMicroelectronics 最大輸入電壓:4.5 V 開關頻率:1.5 MHz 輸出電壓:4.6 V 輸出電流:250 mA 輸出端數量:2 最大工作溫度:+ 85 C 安裝風格:SMD/SMT |
| MAX1774EEI+T | 功能描述:直流/直流開關轉換器 Dual Step-Down w/Switchover RoHS:否 制造商:STMicroelectronics 最大輸入電壓:4.5 V 開關頻率:1.5 MHz 輸出電壓:4.6 V 輸出電流:250 mA 輸出端數量:2 最大工作溫度:+ 85 C 安裝風格:SMD/SMT |
| MAX1774EEI-T | 功能描述:直流/直流開關轉換器 RoHS:否 制造商:STMicroelectronics 最大輸入電壓:4.5 V 開關頻率:1.5 MHz 輸出電壓:4.6 V 輸出電流:250 mA 輸出端數量:2 最大工作溫度:+ 85 C 安裝風格:SMD/SMT |
| MAX1774EGJ | 制造商:Maxim Integrated Products 功能描述: |
| MAX1774EMJ | 功能描述:直流/直流開關轉換器 RoHS:否 制造商:STMicroelectronics 最大輸入電壓:4.5 V 開關頻率:1.5 MHz 輸出電壓:4.6 V 輸出電流:250 mA 輸出端數量:2 最大工作溫度:+ 85 C 安裝風格:SMD/SMT |
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