MAX1837 데이터 시트보기 (PDF) - Maxim Integrated

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MAX1837

24V Internal Switch, 100% Duty Cycle, Step-Down Converters

Maxim Integrated 

MAX1836/MAX1837

24V Internal Switch, 100% Duty Cycle,

Step-Down Converters

Pin Description

PIN NAME

FUNCTION

Dual-Mode Feedback Input. Connect to GND for the preset 3.3V (MAX183_EUT33) or 5.0V (MAX183_

1

FB

EUT50) output. Connect to a resistive divider between the output and FB to adjust the output voltage between

1.25V and VIN, and connect the OUT pin to GND. When setting output voltages above 5.5V, permanently

connect SHDN to IN.

2

GND Ground

3

IN

Input Voltage. 4.5V to 24V input range. Connected to the internal p-channel power MOSFET’s source.

4

LX

Inductor Connection. Connected to the internal p-channel power MOSFET’s drain.

Shutdown Input. A logic-low shuts down the MAX1836/MAX1837 and reduces supply current to 3µA. LX is

5

SHDN high impedance in shutdown. Connect to IN for normal operation. When setting output voltages above 5.5V,

permanently connect SHDN to IN.

Regulated Output Voltage High-Impedance Sense Input. Internally connected to a resistive divider. Connect to

6

OUT the output when using the preset output voltage. Connect to GND when using an external resistive divider to

adjust the output voltage.

—

EP

Exposed Metal Pad. Connect to GND. This pad is internally connected to GND through a soft connect. For

proper grounding and good thermal dissipation. Connect the exposed pad to GND.

INPUT

4.5V OR 12V

CIN

10µF

25V

IN

LX

SHDN

MAX1836

OUT

L1

47µH

D1

OUTPUT

3.3V OR 5V

COUT

100µF

6.3V

INPUT

4.5V OR 12V

CIN

10µF

25V

IN

LX

SHDN

MAX1837

OUT

L1

22µH

D1

OUTPUT

3.3V OR 5V

COUT

150µF

6.3V

GND

FB

GND

FB

CIN = TAIYO YUDEN TMK432BJ106KM

L1 = SUMIDA CDRH5D28-470

COUT = SANYO POSCAP 6TPC100M (SMALLER CAPACITORS CAN BE USED FOR 5V)

D1 = NIHON EP05Q03L

NOTE: HIGH-CURRENT PATHS SHOWN WITH BOLD LINES.

Figure 1. Typical MAX1836 Application Circuit

Detailed Description

The MAX1836/MAX1837 step-down converters are

designed primarily for battery-powered devices, notebook

computers, and industrial control applications. A unique

current-limited control scheme provides high efficiency

over a wide load range. Operation up to 100% duty cycle

allows the lowest possible dropout voltage, increasing

the useable supply voltage range. Under no-load, the

MAX1836/MAX1837 draw only 12μA, and in shutdown

mode, they draw only 3μA to further reduce power con-

sumption and extend battery life. Additionally, an internal

24V switching MOSFET, internal current sensing, and a

CIN = TAIYO YUDEN TMK432BJ106KM

L1 = SUMIDA CDRH5D28-220

COUT = SANYO OS-CON 6SA150M (SMALLER CAPACITORS CAN BE USED FOR 5V)

D1 = NIHON ED05Q03L

NOTE: HIGH-CURRENT PATHS SHOWN WITH BOLD LINES.

Figure 2. Typical MAX1837 Application Circuit

high switching frequency minimize PC board space and

component cost.

Current-Limited Control Architecture

The MAX1836/MAX1837 use a proprietary current-limited

control scheme that operates with duty cycles up to 100%.

These DC-DC converters pulse as needed to maintain

regulation, resulting in a variable switching frequency that

increases with the load. This eliminates the high supply

currents associated with conventional constant-frequency

pulse-width-modulation (PWM) controllers that switch the

MOSFET unnecessarily.

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