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(yè)數(shù)： 14/21頁(yè)
文件大?。?/td> 398K
代理商： MAX1774EEI
The MAX1774 features four separate current-limit
threshold detectors and a watchdog timer for each of its
step-down converters. In addition to the more common
peak-current detector and zero-crossing detector, each
converter also provides a valley-current detector, and a
minimum-current detector. The valley-current detector is
used to force the inductor current to drop to a lower
level after hitting peak current before allowing the P-
channel MOSFET to turn on. This is a safeguard against
inductor current significantly overshooting above the
peak current when the inductor discharges too slowly
when V
OUT
/L is small. The minimum-current detector
ensures that a minimum current is built up in the induc-
tor before turning off the P-channel MOSFET. This helps
the inductor to charge the output near dropout when
the dl/dt is small (because (V
IN
- V
OUT
) / L is small) to
avoid multiple pulses and low efficiency. This feature,
however, is disabled during dropout and light-load con-
ditions where the inductor current may take too long to
reach the minimum current value. A watchdog timer
overrides the minimum current after the P-channel MOS-
FET has been on for longer than about 10μs.
Main S tep-Down Converter
The main step-down converter features adjustable
+1.25V to +5.5V output delivering up to 2A from a
+2.7V to +28V input (see
Setting the Output Voltages
).
The use of external MOSFETs and current-sense resis-
tor maximizes design flexibility. The MAX1774 offers a
synchronous-rectifier MOSFET driver that improves effi-
ciency by eliminating losses through a diode. The two
MOSFET drive outputs, PDRV and NDRV, control these
external MOSFETs. The output swing of these outputs
is limited to reduce power consumption by limiting the
amount of injected gate charge (see
Internal Linear
Regulators
section for details). Current-limit detection
for all main converter current limits is sensed through a
small-sense resistor at the converters
’
output (see
Setting the Current Limit
section ). Driving the
SHDNM
pin low puts the main converter in a low-power shut-
down mode. The core regulator, low-voltage detectors,
and backup converter are still functional when the main
converter is in shutdown. When the MAX1774 enters
backup mode, the main converter and its current sen-
sor are shut off.
Core S tep-Down Converter
The core step-down converter produces a +1.0V to
+5.0V output from a +2.6V to +5.5V input. The low-volt-
age input allows the use of internal power MOSFETs,
taking advantage of their low R
DS(ON)
, improving effi-
ciency and reducing board space. Like the main con-
verter, the core regulator makes use of a synchronous-
rectifying N-channel MOSFET, improving efficiency and
eliminating the need for an external Schottky diode.
Current sensing is internal to the device, eliminating the
need for an external sense resistor. The maximum and
minimum current limits are sensed through the P-chan-
nel MOSFET, while the valley current and zero-crossing
current are sensed through the N-channel MOSFET.
The core output voltage is measured at FBC through a
resistive voltage-divider. This divider can be adjusted
to set the output voltage level (see
Setting the Output
Voltages
). The core input can be supplied from the
main regulator or an external supply that does not
exceed +5.5V (see
High-Voltage Configuration and
Low-Voltage Configuration
sections). The core convert-
er can be shut down independent of the main converter
by driving
SHDNC
low. If the main converter output is
supplying power to the core and is shut down,
SHDNM
controls both outputs. In this configuration, the core
converter continues to operate when the MAX1774 is in
backup mode.
V oltage Monitors and Battery S witc hover
The MAX1774 offers voltage monitors ACI, LBI, DBI,
and
BKOFF
that drive corresponding outputs to indi-
cate low-voltage conditions. The AC adapter low-volt-
age detect input, ACI, is typically connected to the
output of an AC-to-DC converter. When the voltage at
ACI drops below the INS sense input plus 0.22V, the
low AC output,
ACO
, is asserted. Figure 3 shows a sim-
plified block diagram.
The low and dead battery monitors (LBI and DBI) moni-
tor the voltage at MAIN_BATT through a resistive volt-
age-divider. When the voltage at LBI falls below
+1.20V, the low-battery output flag,
LBO,
is asserted.
When both VIN_AC and MAIN_BATT are present, the
MAX1774 chooses one of the two supplies determined
by ACI. To facilitate this, the MAX1774 provides an
open-drain MOSFET driver output (
MDRV
). This drives
an external P-channel MOSFET used to switch the
MAX1774 from the AC input to the battery.
MDRV
goes
low when
ACO
is low, the main battery is not dead, and
the MAX1774 is not in backup mode.
The MAX1774 enters backup mode when the voltage at
DBI is below +1.20V and VIN_AC is not present to the
board. Under these conditions, the
BKUP
output is
asserted (low), and the device utilizes its boost convert-
er and a low-voltage backup battery to supply the main
output. The
BKUP
pin can be driven low externally,
forcing the MAX1774 to enter backup mode. If the volt-
age at
BKOFF
is less than 0.5V, the backup converter
is disabled.
BKOFF
can be driven from a digital signal,
or can be used as a low-battery detector to disable the
backup converter when the backup battery is low.
M
Dual, High-Effic ienc y, S tep-Down
Converter with Bac kup Battery S witc hover
14
______________________________________________________________________________________
相關(guān)PDF資料
PDF描述
MAX1774EMJ 32-Bit Digital Signal Controller with ROM 100-LQFP -40 to 85
MAX1775 32-Bit Digital Signal Controller with ROM 100-LQFP -40 to 125
MAX1775EEE 32-Bit Digital Signal Controller with ROM 100-LQFP -40 to 125
MAX1776 32-Bit Digital Signal Controller with ROM 100-BGA MICROSTAR -40 to 85
MAX1776EUA 24V, 600mA Internal Switch, 100% Duty Cycle, Step-Down Converter
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(kāi)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(kāi)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(kāi)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(kāi)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(kāi)關(guān)轉(zhuǎn)換器 RoHS:否 制造商:STMicroelectronics 最大輸入電壓:4.5 V 開(kāi)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(kāi)關(guān)轉(zhuǎn)換器 RoHS:否 制造商:STMicroelectronics 最大輸入電壓:4.5 V 開(kāi)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
發(fā)布緊急采購(gòu)，3分鐘左右您將得到回復(fù)。

采購(gòu)需求

(若只采購(gòu)一條型號(hào)，填寫(xiě)一行即可)

發(fā)布成功！您可以繼續(xù)發(fā)布采購(gòu)。也可以進(jìn)入我的后臺(tái)，查看報(bào)價(jià)

發(fā)布成功！您可以繼續(xù)發(fā)布采購(gòu)。也可以進(jìn)入我的后臺(tái)，查看報(bào)價(jià)

*型號(hào) *數(shù)量 廠商 批號(hào) 封裝
添加更多采購(gòu)

我的聯(lián)系方式

*
*
*