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參數(shù)資料
| 型號(hào)： | 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(shù)： | 16/21頁 |
| 文件大?。?/td> | 398K |
| 代理商： | MAX1774EEI |
Place 1M
pullup resistors from the main output to
ACO
,
LBO,
and
BKUP
. Use a 1M
pullup resistor from
MDRV
to IN.
When not in backup mode, the backup regulator is iso-
lated from the main output by an internal switch. When
the MAX1774 is in backup mode, the main converter is
disabled, and the output of the backup regulator is
connected to the main output. The core converter is still
operable while in backup mode. The backup step-up
converter cannot drive the typical main load current.
The load at main must be reduced before entering
backup mode.
If
BKUP
is de-asserted (goes high), the MAX1774 exits
backup mode and resumes operation from the main
battery or the AC adapter input. If
BKOFF
goes low, or
the backup battery discharges where it cannot sustain
the main output load, the backup converter shuts off.
To restart the main converter, apply power to V
IN
_
AC
or
MAIN_BATT.
The backup converter uses an external Schottky diode
and internal power NMOS switch. Since this converter
shares the same output as the main buck converter, it
shares the same feedback network. This automatically
sets the backup converter output voltage to that of the
main converter. The backup converter generates an
output between +1.25V and +5.5V from a +0.9V to
+5.5V input, and provides a load current up to 20mA.
When the MAX1774 is in backup mode, the main cur-
rent- sense circuit is turned off to conserve power.
When the output is out of regulation, the maximum
inductor current limit and zero-current detectors regu-
late switching. The N-channel MOSFET is turned on
until the maximum inductor current limit is reached, and
shuts off until the inductor current reaches zero. When
the output is within regulation, switching is controlled
by the maximum pulse width, LXB, switch current limit,
zero crossing, and the feedback voltage.
Internal Linear Regulators
There are two internal linear regulators in the MAX1774.
A high-voltage linear regulator accepts inputs up to
+28V, reducing it to +2.8V at CVL to provide power to
the MAX1774. If the voltage at CS- is greater than
+2.47V, CVL is switched to CS-, allowing it to be driven
from the main converter, improving efficiency. CVL sup-
plies the internal bias to the IC and power for the NDRV
gate driver.
The CVH regulator output provides the low-side voltage
for the main regulator
’
s PDRV output. The voltage at
CVH is regulated at 4.2V below V
IN
to limit the voltage
swing on PDRV, reducing gate charge and improving
efficiency (Figure 3).
Referenc e
The MAX1774 has a trimmed internal +1.25V reference
at REF. REF can source no more than 50μA. Bypass
REF to GND with a 0.22μF capacitor.
Design Proc edure
Low-V oltage Configuration
To improve efficiency and conserve board space, the
core regulator operates from low input voltages, taking
advantage of internal low-voltage, low-on-resistance
MOSFETs. When the input voltage remains below 5.5V,
run the core converter directly from the input by con-
necting INC to IN (Figure 1). This configuration takes
advantage of the core
’
s low-voltage design and
improves efficiency.
High-V oltage Configuration
For input voltages greater than 5.5V, cascade the main
and core converters by connecting INC to the main out-
put voltage (Figure 4). In this configuration, the core
converter is powered from the main output. Ensure that
the main output can simultaneously supply its load and
the core input current.
Bac kup Converter Configuration
The MAX1774 provides a backup step-up converter to
power the device and provide the main output voltage
when other power fails. The backup converter operates
from a +0.9V to +5.5V battery. For most rechargeable
batteries, such as NiCd or NiMH, the simple circuit of
Figure 5 can be used to recharge the backup battery.
In this circuit, the backup battery is charged through
R1 and D10. Consult the battery manufacturer for
charging requirements. To prevent the backup battery
from overdischarging, connect a resistive voltage-
divider from the backup battery to
BKOFF
. Resistor val-
ues can be calculated through the following equation:
R12 = R13
[(V
BU
/ V
BKOFF
) - 1]
where V
BKOFF
= 0.5V, and V
BU
is the minimum accept-
able backup battery voltage. Choose R13 to be less
than 150k
.
S etting the Output V oltages
The main output voltage is set from +1.25V and +5.5V
with two external resistors connected as a voltage-
divider to FBM (Figure 1). Resistor values can be calcu-
lated by the following equation:
R10 = R11
[(V
OUTM
/ V
FBM
) - 1]
where V
FBM
= +1.25V. Choose R11 to be 40k
or less.
The core regulator output is adjustable from +1.0V to
+5.0V through two external resistors connected as a
M
Dual, High-Effic ienc y, S tep-Down
Converter with Bac kup Battery S witc hover
16
______________________________________________________________________________________
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相關(guān)代理商/技術(shù)參數(shù) |
參數(shù)描述 |
|---|---|
| MAX1774EEI+ | 功能描述:直流/直流開關(guān)轉(zhuǎn)換器 Dual Step-Down w/Switchover 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 |
| MAX1774EEI+T | 功能描述:直流/直流開關(guān)轉(zhuǎn)換器 Dual Step-Down w/Switchover 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 |
| MAX1774EEI-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 |
| MAX1774EGJ | 制造商:Maxim Integrated Products 功能描述: |
| MAX1774EMJ | 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 |
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