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| 型号： | MAX1774EEI+T |
| 厂商： | Maxim Integrated Products |
| 文件页数： | 13/21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
TOFFMIN
V MIN
CS+
TONMIN
CS-
V VALLEY
FB
S
Q
PON
PON
V IN
PSW
REF
R
V O
V CLM
S
Q
NON
NSW
R
V ZERO
NONOVERLAP
PROTECTION
Figure 2. Simplified Control System Block Diagram
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 Scheme
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.
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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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