Datasheet

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
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.
Figure 1. Typical MAX1836 Application Circuit Figure 2. Typical MAX1837 Application Circuit
PIN NAME FUNCTION
1 FB
Dual-Mode Feedback Input. Connect to GND for the preset 3.3V (MAX183_EUT33) or 5.0V (MAX183_
EUT50) output. Connect to a resistive divider between the output and FB to adjust the output voltage between
1.25V and V
IN
, 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.
5 SHDN
Shutdown Input. A logic-low shuts down the MAX1836/MAX1837 and reduces supply current to 3µA. LX is
high impedance in shutdown. Connect to IN for normal operation. When setting output voltages above 5.5V,
permanently connect SHDN to IN.
6 OUT
Regulated Output Voltage High-Impedance Sense Input. Internally connected to a resistive divider. Connect to
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.
MAX1836
IN
GND
LX
FB
OUT
OUTPUT
3.3V OR 5V
INPUT
4.5V OR 12V
C
IN
10µF
25V
D1
L1
47µH
C
OUT
100µF
6.3V
C
IN
= TAIYO YUDEN TMK432BJ106KM
L1 = SUMIDA CDRH5D28-470
C
OUT
= SANYO POSCAP 6TPC100M (SMALLER CAPACITORS CAN BE USED FOR 5V)
D1 = NIHON EP05Q03L
NOTE: HIGH-CURRENT PATHS SHOWN WITH BOLD LINES.
SHDN
MAX1837
IN
GND
LX
SHDN
FB
OUT
OUTPUT
3.3V OR 5V
INPUT
4.5V OR 12V
C
IN
10µF
25V
D1
L1
22µH
C
OUT
150µF
6.3V
C
IN
= TAIYO YUDEN TMK432BJ106KM
L1 = SUMIDA CDRH5D28-220
C
OUT
= SANYO OS-CON 6SA150M (SMALLER CAPACITORS CAN BE USED FOR 5V)
D1 = NIHON ED05Q03L
NOTE: HIGH-CURRENT PATHS SHOWN WITH BOLD LINES.
MAX1836/MAX1837 24V Internal Switch, 100% Duty Cycle,
Step-Down Converters
www.maximintegrated.com
Maxim Integrated │ 7
Pin Description