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参数资料
| 型号： | MAX1734EUK18+T |
| 厂商： | Maxim Integrated Products |
| 文件页数： | 6/8页 |
| 文件大小： | 0K |
| 描述： | IC REG BUCK SYNC 1.8V SOT23-5 |
| 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： | 固定 |
| 输出数： | 1 |
| 输出电压： | 1.8V |
| 输入电压： | 2.7 V ~ 5.5 V |
| 频率 - 开关： | 1.2MHz |
| 电流 - 输出： | 250mA |
| 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： | SC-74A，SOT-753 |
| 包装： | 带卷 (TR) |
| 供应商设备封装： | SOT-23-5 |
Low-Voltage, Step-Down DC-DC Converters
in SOT23
INPUT
+2.7V TO +5.5V
IN
LX
L1
10 μ H
V OUT
IN
C1
2.2 μ F
MAX1733
R1
C2
22 μ F
MAX1733
MAX1734
CURRENT
LIMIT
SHDN
FB
R2
GND
DIGITAL
SOFT-START
CONTROL
P
Figure 1. MAX1733 Typical Application Circuit
LOGIC
N
LX
Detailed Description
The MAX1733/MAX1734 step-down DC-DC converters
deliver over 250mA to outputs as low as 1.25V. They
use a unique proprietary current-limited control scheme
SHDN
SHUTDOWN
CONTROL
V REF
OUT (FB)
that maintains extremely low quiescent supply current
(40μA), and their high 1.2MHz (max) operating frequen-
( ) ARE FOR MAX1733 ONLY.
GND
cy permits small, low-cost external components. Figure
2 is a simplified functional diagram.
Control Scheme
The MAX1733/MAX1734 use a proprietary, current-lim-
ited control scheme to ensure high-efficiency, fast tran-
sient 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 reg-
ulation. 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 synchronous rectifier
eliminates the need for an external Schottky diode.
This control scheme allows the MAX1733/MAX1734 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
efficiency and reduced output voltage ripple. When
delivering medium and higher output currents, the
MAX1733/MAX1734 extend either the on-time or the off-
time, as necessary to maintain regulation, resulting in
Figure 2. Simplified Functional Diagram
nearly constant frequency operation with high efficien-
cy and low output voltage ripple.
Shutdown Mode
Connecting SHDN to GND places the MAX1733/
MAX1734 in shutdown mode and reduces supply cur-
rent to 0.01μA. In shutdown, the control circuitry, inter-
nal switching MOSFET, and synchronous rectifier turn
off and LX goes high impedance. Connect SHDN to IN
for normal operation.
Soft-Start
The MAX1733/MAX1734 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 alkaline cells.
Soft-start is implemented by starting with the current limit
at 25% of its full current value and gradually increasing it
in 25% steps until the full current limit is reached. See
Soft-Start and Shutdown Response in the Typical
Operating Characteristics section.
Design Information
Setting the Output Voltage (MAX1733)
Select an output voltage for the MAX1733 by connect-
ing FB to a resistive divider between the output and
6
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