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参数资料
| 型号： | MAX1857EUA47 |
| 厂商： | MAXIM INTEGRATED PRODUCTS INC |
| 元件分类： | 基准电压源/电流源 |
| 英文描述： | 500mA, Low-Dropout, Ripple-Rejecting LDO in MAX |
| 中文描述： | FIXED/ADJUSTABLE POSITIVE LDO REGULATOR, 0.175 V DROPOUT, PDSO8 |
| 封装： | MICRO MAX PACKAGE-8 |
| 文件页数： | 7/10页 |
| 文件大小： | 245K |
| 代理商： | MAX1857EUA47 |
Detailed Description
The MAX1857 is a low-dropout, low-quiescent-current
ripple rejector designed primarily for audio and video
applications. The device supplies loads up to 500mA
and is available with a preset output voltage of 4.75V.
As shown in Figure 1, the MAX1857 consists of a 1.25V
reference, error amplifier, P-channel pass transistor,
and internal feedback voltage-divider.
The 1.25V reference is connected to the error amplifier,
which compares this reference with the feedback volt-
age and amplifies the difference. If the feedback volt-
age is lower than the reference voltage, the
pass-transistor gate is pulled lower, which allows more
current to pass to the output and increases the output
voltage. If the feedback voltage is too high, the pass-
transistor gate is pulled up, allowing less current to
pass to the output.
The output voltage is fed back through either an inter-
nal resistive divider connected to OUT or an external
resistor network connected to SET. The dual-mode
comparator examines V
SET
and selects the feedback
path. If V
SET
is below 50mV, the internal feedback path
is used and the output is regulated to the factory-preset
voltage.
Additional blocks include an output current limiter,
reset comparator, thermal sensor, and shutdown logic.
Internal P-Channel Pass Transistor
The MAX1857 features a 0.25
P-channel MOSFET
pass transistor. Unlike similar designs using PNP pass
transistors, P-channel MOSFETs require no base drive,
which reduces quiescent current. PNP-based regula-
tors also waste considerable current in dropout when
the pass transistor saturates, and use high base-drive
currents under large loads. The MAX1857 does not suf-
fer from these problems and consumes only 175μA of
quiescent current under heavy loads as well as in
dropout.
Output Voltage Selection
The MAX1857
’
s dual-mode operation allows operation
in either a preset voltage mode or an adjustable mode.
Connect SET to GND to select the preset output volt-
age. The two-digit part number suffix identifies the out-
put voltage (see
Selector Guide
). For example, the
MAX1857EUA47 has a preset 4.75V output voltage.
The output voltage may also be adjusted by connecting
a voltage-divider from OUT to SET (Figure 2). Select R2
in the 25k
to 100k
range. Calculate R1 with the fol-
lowing equation:
R1 = R2 [(V
OUT
/ V
SET
)
–
1]
where V
SET
= 1.25V, and V
OUT
may range from 1.25V
to 5.0V.
Shutdown
Pull
SHDN
low to enter shutdown. During shutdown, the
output is disconnected from the input and supply current
drops to 0.1μA. When in shutdown,
RST
pulls low and
OUT is discharged through an internal 5k
resistor. The
capacitance and load at OUT determine the rate at
which V
OUT
decays.
SHDN
can be pulled as high as 6V,
regardless of the input and output voltage.
Reset Output
The reset output (
RST
) pulls low when OUT is less than
86% of the nominal regulation voltage. Once OUT
exceeds 86% of the nominal voltage,
RST
goes high
impedance after 4.5ms.
RST
is an open-drain N-channel
output. To obtain a voltage at
RST
, connect a pullup
resistor from
RST
to OUT. A 100k
resistor works well for
most applications.
RST
can be used as a power-on-reset
(POR) signal to a microcontroller (μC), or drive an exter-
nal LED to indicate power failure. When the MAX1857 is
M
500mA, Low-Dropout,
Ripple-Rejecting LDO in μMAX
_______________________________________________________________________________________
7
OUT
OUT
SET
GND
IN
IN
SHDN
RST
C
OUT
3.3
μ
F
V
OUT
V
OUT
1.25V
C
IN
1
μ
F
ON
OFF
V
IN
= +2.5V TO +5.5V
R
2
R1 = R2
- 1
MAX1857
R
1
Figure 2. Adjustable Output Using External Feedback
Resistors
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相关代理商/技术参数 |
参数描述 |
|---|---|
| MAX1857EUA47+ | 功能描述:低压差稳压器 - LDO 500mA Ripple-Rejecting RoHS:否 制造商:Texas Instruments 最大输入电压:36 V 输出电压:1.4 V to 20.5 V 回动电压（最大值）:307 mV 输出电流:1 A 负载调节:0.3 % 输出端数量: 输出类型:Fixed 最大工作温度:+ 125 C 安装风格:SMD/SMT 封装 / 箱体:VQFN-20 |
| MAX1857EUA47+T | 功能描述:低压差稳压器 - LDO 500mA Ripple-Rejecting RoHS:否 制造商:Texas Instruments 最大输入电压:36 V 输出电压:1.4 V to 20.5 V 回动电压（最大值）:307 mV 输出电流:1 A 负载调节:0.3 % 输出端数量: 输出类型:Fixed 最大工作温度:+ 125 C 安装风格:SMD/SMT 封装 / 箱体:VQFN-20 |
| MAX1857EUA47-T | 功能描述:低压差稳压器 - LDO 500mA Ripple-Rejecting RoHS:否 制造商:Texas Instruments 最大输入电压:36 V 输出电压:1.4 V to 20.5 V 回动电压（最大值）:307 mV 输出电流:1 A 负载调节:0.3 % 输出端数量: 输出类型:Fixed 最大工作温度:+ 125 C 安装风格:SMD/SMT 封装 / 箱体:VQFN-20 |
| MAX1858AEEG | 功能描述:DC/DC 开关控制器 RoHS:否 制造商:Texas Instruments 输入电压:6 V to 100 V 开关频率: 输出电压:1.215 V to 80 V 输出电流:3.5 A 输出端数量:1 最大工作温度:+ 125 C 安装风格: 封装 / 箱体:CPAK |
| MAX1858AEEG+ | 功能描述:电压模式 PWM 控制器 Dual 180 Out Buck Controllers RoHS:否 制造商:Texas Instruments 输出端数量:1 拓扑结构:Buck 输出电压:34 V 输出电流: 开关频率: 工作电源电压:4.5 V to 5.5 V 电源电流:600 uA 最大工作温度:+ 125 C 最小工作温度:- 40 C 封装 / 箱体:WSON-8 封装:Reel |
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