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参数资料
| 型号： | MAX1837EUT50#TG16 |
| 厂商： | Maxim Integrated Products |
| 文件页数： | 9/15页 |
| 文件大小： | 0K |
| 描述： | IC REG BUCK 5V 0.25A SOT23-6 |
| 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： | 5V |
| 输入电压： | 4.5 V ~ 24 V |
| 电流 - 输出： | 250mA |
| 同步整流器： | 无 |
| 工作温度： | -40°C ~ 85°C |
| 安装类型： | 表面贴装 |
| 封装/外壳： | SOT-23-6 |
| 包装： | 带卷 (TR) |
| 供应商设备封装： | SOT-6 |
24V Internal Switch, 100% Duty Cycle,
Step-Down Converters
R1 = R2 ? ? OUT ? - 1 ?
Input-Output (Dropout) Voltage
A step-down converter’s minimum input-to-output volt-
age differential (dropout voltage) determines the lowest
useable input supply voltage. In battery-powered sys-
tems, this limits the useful end-of-life battery voltage. To
maximize battery life, the MAX1836/MAX1837 operate
with duty cycles up to 100%, which minimizes the input-
to-output voltage differential. When the supply voltage
approaches the output voltage, the P-channel MOSFET
remains on continuously to supply the load.
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. For a
step-down converter with 100% duty cycle, the dropout
voltage depends on the MOSFET drain-to-source on-
resistance (R DS(ON) ) and inductor series resistance;
therefore, it is proportional to the load current:
(see the Selector Guide ). For example, the
MAX1836EUT33 has a preset 3.3V output voltage.
The MAX1836/MAX1837 output voltage may be adjust-
ed by connecting a voltage divider from the output to
FB (Figure 5). When externally adjusting the output volt-
age, connect OUT to GND. Select R2 in the 10k ? to
100k ? range. Calculate R1 with the following equation:
? ? V ? ?
? ?
? ? V FB ? ?
where V FB = 1.25V, and V OUT may range from 1.25V to
V IN . When setting output voltages above 5.5V, the shut-
down feature cannot be used, so SHDN must be per-
manently connected to IN.
Inductor Selection
V DROPOUT = I OUT × ( R DS(ON) + R INDUCTOR
)
When selecting the inductor, consider these four para-
meters: inductance value, saturation current rating,
series resistance, and size. The MAX1836/MAX1837
Shutdown ( SHDN )
A logic-level low voltage on SHDN shuts down the
MAX1836/MAX1837. When shut down, the supply current
drops to 3μA to maximize battery life, and the internal P-
operate with a wide range of inductance values. For
most applications, values between 10μH and 100μH
work best with the controller ’s switching frequency.
Calculate the minimum inductance value as follows:
channel MOSFET turns off to isolate the output from the
input. The output capacitance and load current determine
the rate at which the output voltage decays. A logic-level
high voltage on SHDN activates the MAX1836/MAX1837.
L (MIN) =
(V IN(MAX) - V OUT ) t ON(MIN)
I LIM
Do not leave SHDN floating. If unused, connect SHDN to
IN. When setting output voltages above 5.5V, the shut-
down feature cannot be used, so SHDN must be perma-
nently connected to IN. The SHDN input voltage slew rate
must be greater than 10V/ms.
Thermal-Overload Protection
Thermal-overload protection limits total power dissipa-
tion in the MAX1836/MAX1837. When the junction tem-
perature exceeds T J = +160°C, a thermal sensor turns
where t ON(MIN) = 1.0μs. Inductor values up to six times
L (MIN) are acceptable. Low-value inductors may be
smaller in physical size and less expensive, but they
result in higher peak-current overshoot due to current-
sense comparator propagation delay (300ns). Peak-
current overshoot reduces efficiency and could exceed
the current ratings of the internal switching MOSFET
and external components.
off the pass transistor, allowing the IC to cool. The ther-
mal sensor turns the pass transistor on again after the
INPUT
4.5V OR 24V
L1
OUTPUT
1.25V TO V IN
IC’s junction temperature cools by 10°C, resulting in
a pulsed output during continuous thermal-overload
conditions.
C IN
IN
SHDN
LX
D1
R1
C OUT
Design Information
MAX1836
FB
Output Voltage Selection
The feedback input features dual-mode operation.
Connect the output to OUT and FB to GND for the pre-
set output voltage. The MAX1836/MAX1837 are sup-
GND
MAX1837
OUT
R2
plied with factory-set output voltages of 3.3V or 5V. The
NOTE: HIGH-CURRENT PATHS SHOWN WITH BOLD LINES.
two-digit part number suffix identifies the output voltage
Figure 5. Adjustable Output Voltage
_______________________________________________________________________________________
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