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| 型号： | MAX1774EEI+T |
| 厂商： | Maxim Integrated Products |
| 文件页数： | 14/21页 |
| 文件大小： | 0K |
| 描述： | IC REG BUCK SYNC ADJ DL 28QSOP |
| 产品培训模块： | Lead (SnPb) Finish for COTS Obsolescence Mitigation Program |
| 标准包装： | 2,500 |
| 类型： | 降压（降压） |
| 输出类型： | 可调式 |
| 输出数： | 2 |
| 输出电压： | 1 V ~ 5.5 V |
| 输入电压： | 2.7 V ~ 28 V |
| 频率 - 开关： | 1.25MHz |
| 电流 - 输出： | 1.5A，2A |
| 同步整流器： | 是 |
| 工作温度： | -40°C ~ 85°C |
| 安装类型： | 表面贴装 |
| 封装/外壳： | 28-SSOP（0.154"，3.90mm 宽） |
| 包装： | 带卷 (TR) |
| 供应商设备封装： | 28-QSOP |
Dual, High-Efficiency, Step-Down
Converter with Backup Battery Switchover
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 Step-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 Step-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.
Voltage Monitors and Battery Switchover
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.
14
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相关代理商/技术参数 |
参数描述 |
|---|---|
| MAX1774EGJ | 制造商:Maxim Integrated Products 功能描述: |
| MAX1774EMJ | 功能描述:直流/直流开关转换器 RoHS:否 制造商:STMicroelectronics 最大输入电压:4.5 V 开关频率:1.5 MHz 输出电压:4.6 V 输出电流:250 mA 输出端数量:2 最大工作温度:+ 85 C 安装风格:SMD/SMT |
| MAX1774EVKIT | 功能描述:直流/直流开关转换器 Evaluation Kit for the MAX1774 RoHS:否 制造商:STMicroelectronics 最大输入电压:4.5 V 开关频率:1.5 MHz 输出电压:4.6 V 输出电流:250 mA 输出端数量:2 最大工作温度:+ 85 C 安装风格:SMD/SMT |
| MAX1775EEE | 功能描述:直流/直流开关转换器 Dual-Out Step-Down for PDA/Palmtop RoHS:否 制造商:STMicroelectronics 最大输入电压:4.5 V 开关频率:1.5 MHz 输出电压:4.6 V 输出电流:250 mA 输出端数量:2 最大工作温度:+ 85 C 安装风格:SMD/SMT |
| MAX1775EEE+ | 功能描述:直流/直流开关转换器 Dual-Out Step-Down for PDA/Palmtop RoHS:否 制造商:STMicroelectronics 最大输入电压:4.5 V 开关频率:1.5 MHz 输出电压:4.6 V 输出电流:250 mA 输出端数量:2 最大工作温度:+ 85 C 安装风格:SMD/SMT |
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