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參數(shù)資料
| 型號： | MAX1921EUT |
| 廠商： | Maxim Integrated Products, Inc. |
| 英文描述： | PLASTIC ENCAPSULATED DEVICES |
| 中文描述： | 塑封器件 |
| 文件頁數(shù)： | 5/9頁 |
| 文件大?。?/td> | 370K |
| 代理商： | MAX1921EUT |
Detailed Description
The MAX1920/MAX1921 step-down DC-DC converters
deliver over 400mA to outputs as low as 1.25V. They use
a unique proprietary current-limited control scheme that
maintains extremely low quiescent supply current (50μA),
and their high 1.2MHz (max) operating frequency permits
small, low-cost external components.
Control Scheme
The MAX1920/MAX1921 use a proprietary, current-limited
control scheme to ensure high-efficiency, fast transient
response, and physically small external components. This
control scheme is simple: when the output voltage is out
of regulation, the error comparator begins a switching
cycle by turning on the high-side switch. This switch
remains on until the minimum on-time of 400ns expires
and the output voltage regulates or the current-limit
threshold is exceeded. Once off, the high-side switch
remains off until the minimum off-time of 400ns expires
and the output voltage falls out of regulation. During this
period, the low-side synchronous rectifier turns on and
remains on until either the high-side switch turns on again
or the inductor current approaches zero. The internal syn-
chronous rectifier eliminates the need for an external
Schottky diode.
This control scheme allows the MAX1920/MAX1921 to
provide excellent performance throughout the entire
load-current range. When delivering light loads, the
high-side switch turns off after the minimum on-time to
reduce peak inductor current, resulting in increased effi-
ciency and reduced output voltage ripple. When deliver-
ing medium and higher output currents, the
MAX1920/MAX1921 extend either the on-time or the off-
time, as necessary to maintain regulation, resulting in
nearly constant frequency operation with high-efficiency
and low-output voltage ripple.
Shutdown Mode
Connecting
SHDN
to GND places the MAX1920/
MAX1921 in shutdown mode and reduces supply cur-
rent to 0.1μA. In shutdown, the control circuitry, internal
switching MOSFET, and synchronous rectifier turn off
and LX becomes high impedance. Connect
SHDN
to
IN for normal operation.
Soft-Start
The MAX1920/MAX1921 have internal soft-start circuitry
that limits current draw at startup, reducing transients
on the input source. Soft-start is particularly useful for
higher impedance input sources, such as Li+ and alka-
line cells. Soft-start is implemented by starting with the
current limit at 25% of its full current value and gradual-
ly increasing it in 25% steps until the full current limit is
reached. See Soft-Start and Shutdown Response in the
Typical Operating Characteristics
.
M
Low-Voltage, 400mA Step-Down
DC-DC Converters in SOT23
_______________________________________________________________________________________
5
Pin Description
PIN
NAME
FUNCTION
1
IN
Supply voltage input for MAX1921EUT15 and MAX1921EUT18 is 2V to 5.5V. Supply voltage input for
MAX1920 and other voltage versions of MAX1921 is 2.5V to 5.5V. Bypass IN to GND with a 2.2μF ceramic
capacitor as close to IN as possible.
2
AGND
Analog Ground. Connect to PGND.
3
SHDN
Active-Low Shutdown Input. Connect
SHDN
to IN for normal operation. In shutdown, LX becomes
high-impedance and quiescent current drops to 0.1μA.
OUT
MAX1921 Voltage Sense Input. OUT is connected to an internal voltage-divider.
4
FB
MAX1920 Voltage Feedback Input. FB regulates to 1.25V nominal. Connect FB to an external resistive
voltage-divider between the output voltage and GND.
5
6
PGND
LX
Power Ground. Connect to AGND.
Inductor Connection
MAX1921
AGND
IN
SHDN
LX
PGND
OUT
OFF
ON
R1
C
OUT
L
C
FF
OUTPUT
UP TO 400mA
INPUT
2V TO 5.5V
C
IN
1
2
3
4
5
6
Figure 1. Typical Output Application Circuit (MAX1921)
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PDF描述 |
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| MAX1920EUT-T | Low-Voltage, 400mA Step-Down DC-DC Converters in SOT23 |
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| MAX1922 | 1A Current-Limited Switch for 2 USB Ports |
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相關(guān)代理商/技術(shù)參數(shù) |
參數(shù)描述 |
|---|---|
| MAX1921EUT15 | 制造商:Maxim Integrated Products 功能描述:LOW-VOLTAGE 400MA STEP-DOWN DC-DC - Cut Tape Product |
| MAX1921EUT15+ | 制造商:Maxim Integrated Products 功能描述:LOW-VOLTAGE 400MA STEP-DOWN DC-DC - Rail/Tube |
| MAX1921EUT15+T | 功能描述:直流/直流開關(guān)轉(zhuǎn)換器 400mA Step-Down DC/DC Converter 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 |
| MAX1921EUT15-T | 功能描述:直流/直流開關(guān)轉(zhuǎn)換器 400mA Step-Down DC/DC Converter 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 |
| MAX1921EUT18 | 制造商:Maxim Integrated Products 功能描述:LOW-VOLTAGE 400MA STEP-DOWN DC-DC - Rail/Tube |
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