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参数资料
| 型号： | MAX1837EUT50-T |
| 厂商： | MAXIM INTEGRATED PRODUCTS INC |
| 元件分类： | 稳压器 |
| 英文描述： | 24V Internal Switch, 100% Duty Cycle, Step-Down Converters |
| 中文描述： | 0.9 A SWITCHING REGULATOR, PDSO6 |
| 封装： | MO-178AB, SOT-23, 6 PIN |
| 文件页数： | 9/13页 |
| 文件大小： | 394K |
| 代理商： | MAX1837EUT50-T |
M
24V Internal Switch, 100% Duty Cycle,
Step-Down Converters
_______________________________________________________________________________________
9
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:
(
Shutdown (
SHDN
)
A logic-level low voltage on
SHDN
shuts down the
MAX1836/MAX1837. When shut down, the supply cur-
rent drops to 3μA to maximize battery life, and the inter-
nal P-channel MOSFET turns off to isolate the output
from the input. The output capacitance and load cur-
rent determine the rate at which the output voltage
decays. A logic-level high voltage on
SHDN
activates
the MAX1836/MAX1837. Do not leave
SHDN
floating. If
unused, connect
SHDN
to IN. When setting output volt-
ages above 5.5V, the shutdown feature cannot be
used, so
SHDN
must be permanently 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
off the pass transistor, allowing the IC to cool. The ther-
mal sensor turns the pass transistor on again after the
IC
’
s junction temperature cools by 10
°
C, resulting in
a pulsed output during continuous thermal-overload
conditions.
Design Information
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-
plied with factory-set output voltages of 3.3V or 5V. The
two-digit part number suffix identifies the output voltage
(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:
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
When selecting the inductor, consider these four para-
meters: inductance value, saturation current rating,
series resistance, and size. The MAX1836/MAX1837
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:
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.
L
(V
-V
)
I
(MIN)
IN(MAX)
OUT
ON(MIN)
LIM
=
t
R1 R2
V
V
-
OUT
FB
1
V
DROPOUT
OUT
I
DS(ON)
R
INDUCTOR
R
=
×
+
)
MAX1836
MAX1837
IN
GND
LX
SHDN
FB
OUT
NOTE:
HIGH-CURRENT PATHS SHOWN WITH BOLD LINES.
OUTPUT
1.25V TO V
IN
INPUT
4.5V OR 24V
C
IN
D1
L1
C
OUT
R1
R2
Figure 5. Adjustable Output Voltage
相关PDF资料 |
PDF描述 |
|---|---|
| MAX1836EUT33 | COIL 330UH 240MA CHOKE SMD |
| MAX1836EUT50 | COIL 39UH 650MA CHOKE SMD |
| MAX1836EUT50-T | COIL 390UH 210MA CHOKE SMD |
| MAX1837EUT33 | CHOKE COIL 100UH 600MA SMD |
| MAX1836-MAX1837 | 24V Internal Switch, 100% Duty Cycle, Step-Down Converters |
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