Datasheet

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General Description

The MAX1836/MAX1837 high-efficiency step-down

converters provide a preset 3.3V or 5V output voltage

from supply voltages as high as 24V. Using external

feedback resistors, the output voltage may be adjusted

from 1.25V to V

. An internal current-limited switching

MOSFET delivers load currents up to 125mA

(MAX1836) or 250mA (MAX1837).

The unique current-limited control scheme, operating

with duty cycles up to 100%, minimizes the dropout

voltage (120mV at 100mA). Additionally, this control

scheme reduces supply current under light loads to

12µA. High switching frequencies allow the use of tiny

surface-mount inductors and output capacitors.

The MAX1836/MAX1837 step-down converters with

internal switching MOSFETs are available in 6-pin

SOT23 and 3mm x 3mm TDFN packages, making them

ideal for low-cost, low-power, space-sensitive applica-

tions. For increased output drive capability, use the

MAX1776 step-down converter that uses an internal

24V switch to deliver up to 500mA. For even higher cur-

rents, use the MAX1626/ MAX1627 step-down con-

trollers that drive an external P-channel MOSFET to

deliver up to 20W.

Applications

9V Battery Systems

Notebook Computers

Distributed Power Systems

Backup Supplies

4mA to 20mA Loop Power Supplies

Industrial Control Supplies

Handheld Devices

____________________________Features

♦ 4.5V to 24V Input Voltage Range

♦ Preset 3.3V or 5V Output

♦ Adjustable Output from 1.25V to V

♦ Output Currents Up to 125mA (MAX1836) or

250mA (MAX1837)

♦ Efficiency Over 90%

♦ 12µA Quiescent Current

♦ 3µA Shutdown Current

♦ 100% Maximum Duty Cycle for Low Dropout

♦ Small 6-Pin SOT23 and TDFN Packages

MAX1836/MAX1837

24V Internal Switch, 100% Duty Cycle,

Step-Down Converters

________________________________________________________________ Maxim Integrated Products 1

19-1919; Rev 3; 7/06

For pricing, delivery, and ordering information, please contact Maxim/Dallas Direct! at

1-888-629-4642, or visit Maxim’s website at www.maxim-ic.com.

MAX1836

MAX1837

GND

SHDN

OUT

NOTE: HIGH-CURRENT PATHS SHOWN WITH BOLD LINES.

OUTPUT

3.3V OR 5V

INPUT

4.5V TO 24V

Typical Operating Circuit

GND

LXIN

16OUT

5 SHDN

MAX1836

MAX1837

MAX1836

MAX1837

SOT23

TDFN

TOP VIEW

GND

1FB

6 OUT

5 SHDN

Pin Configurations

PART

TEMP RANGE

PIN-

PACKAGE

TOP

MARK

MAX1836ETT33-T

-40°C to +85°C 6 TDFN-EP*

AJG

MAX1836ETT50-T

-40°C to +85°C 6 TDFN-EP*

AJE

MAX1836EUT33-T

-40°C to +85°C 6 SOT23-6

AANY

MAX1836EUT50-T

-40°C to +85°C 6 SOT23-6

AANW

MAX1837ETT33-T

-40°C to +85°C 6 TDFN-EP*

AJH

MAX1837ETT50-T

-40°C to +85°C 6 TDFN-EP*

AJF

MAX1837EUT33-T

-40°C to +85°C 6 SOT23-6

AANZ

MAX1837EUT50-T

-40°C to +85°C 6 SOT23-6

AANX

Ordering Information

Selector Guide appears at end of data sheet.

*EP = Exposed pad.

Summary of content (15 pages)

PAGE 1
9-1919; Rev 3; 7/06 24V Internal Switch, 100% Duty Cycle, Step-Down Converters The MAX1836/MAX1837 high-efficiency step-down converters provide a preset 3.3V or 5V output voltage from supply voltages as high as 24V. Using external feedback resistors, the output voltage may be adjusted from 1.25V to VIN. An internal current-limited switching MOSFET delivers load currents up to 125mA (MAX1836) or 250mA (MAX1837).
PAGE 2
MAX1836/MAX1837 24V Internal Switch, 100% Duty Cycle, Step-Down Converters ABSOLUTE MAXIMUM RATINGS IN, SHDN to GND ...................................................-0.3V to +25V LX to GND.......................................................-2V to (VIN + 0.3V) OUT, FB to GND.......................................................-0.3V to +6V Continuous Power Dissipation (TA = +70°C) (Note 1) 6-Pin SOT23 (derate 8.7mW/°C above +70°C)............696mW 6-Pin TDFN (derate 24.4mW/°C above +70°C) .........
PAGE 3
24V Internal Switch, 100% Duty Cycle, Step-Down Converters (Circuits of Figures 1 (MAX1836) and 2 (MAX1837), VIN = 12V, SHDN = IN, TA = 0°C to +85°C. Typical values are at TA = +25°C, unless otherwise noted.) PARAMETER SYMBOL CONDITIONS Zero-Crossing Timeout LX does not rise above the threshold LX Switch Leakage Current VIN = 18V, LX = GND, TA = +25°C Dropout Voltage VDROPOUT MIN TYP MAX UNITS 1 µA 30 µs IOUT = 100mA, VIN = 5V 120 mV Line Regulation VIN = 5V to 24V 0.
PAGE 4
ELECTRICAL CHARACTERISTICS (continued) (Circuits of Figures 1 (MAX1836) and 2 (MAX1837), VIN = 12V, SHDN = IN, TA = -40°C to +85°C, unless otherwise noted.) (Note 4) PARAMETER SYMBOL CONDITIONS MIN LX Zero-Crossing Threshold MAX UNITS -75 TYP +75 mV Shutdown Input Threshold V SHDN VIN = 4.5V to 24V (Note 3) 0.8 2.4 V Shutdown Leakage Current ISHDN V SHDN = 0 or 24V -1 +1 µA Note 2: When using the shutdown input, the maximum output voltage allowed with external feedback is 5.5V.
PAGE 5
24V Internal Switch, 100% Duty Cycle, Step-Down Converters (Circuits of Figures 1 (MAX1836) and 2 (MAX1837), VIN = 12V, SHDN = IN, TA = +25°C.) 80 FIGURE 2 VOUT = 3.3V L1 = 47µH 10 IOUT = 10mA 75 IOUT = 10mA 70 1000 800 8 12 16 20 24 IOUT = 10mA 400 200 LIMITED BY tON(MIN) 0 0 4 INPUT VOLTAGE (V) 8 12 16 20 0 24 4 VIN = 12V TO 24V VIN = 9V 100 5.00 VIN = 7V VIN = 9V VIN = 7V 4.98 FIGURE 6 VOUT = 5V 95 EFFICIENCY (%) 5.02 8 12 16 20 24 MAX1837EUT50 EFFICIENCY vs.
PAGE 6
MAX1836/MAX1837 24V Internal Switch, 100% Duty Cycle, Step-Down Converters Typical Operating Characteristics (continued) (Circuits of Figures 1 (MAX1836) and 2 (MAX1837), VIN = 12V, SHDN = IN, TA = +25°C.) MAX1837EUT50 LINE TRANSIENT MAX1837EUT50 LOAD TRANSIENT MAX1836/7 toc15 MAX1836/7 toc14 20V 400mA 200mA A 0 0 5.02V 5.1V 5.00V B 4.9V 750mA 500mA C B 5.0V 4.
PAGE 7
24V Internal Switch, 100% Duty Cycle, Step-Down Converters 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 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.
PAGE 8
MAX1836/MAX1837 24V Internal Switch, 100% Duty Cycle, Step-Down Converters INPUT 4.5V OR 24V CIN L1 LX IN SHDN OUTPUT 3.3V OR 5V D1 COUT VSENSE OUT R Q FB MAXIMUM OFF-TIME DELAY S Q TRIG 100mV Q TRIG MAXIMUM ON-TIME DELAY VSET 1.25V GND MAX1836 MAX1837 Figure 3. Functional Diagram When the output voltage is too low, an error comparator sets a flip-flop, which turns on the internal p-channel MOSFET and begins a switching cycle (Figure 3).
PAGE 9
24V Internal Switch, 100% Duty Cycle, Step-Down Converters ( VDROPOUT = IOUT × RDS(ON) + RINDUCTOR ) 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 Pchannel 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.
PAGE 10
MAX1836/MAX1837 24V Internal Switch, 100% Duty Cycle, Step-Down Converters The inductor’s saturation current rating must be greater than the peak switching current, which is determined by the switch current limit plus the overshoot due to the 300ns current-sense comparator propagation delay: IPEAK = ILIM + (VIN - VOUT ) 300ns L where the switch current-limit (ILIM) is typically 312mA (MAX1836) or 625mA (MAX1837).
PAGE 11
24V Internal Switch, 100% Duty Cycle, Step-Down Converters MAX1836/MAX1837 Table 1. Component Suppliers SUPPLIER PHONE FAX WEBSITE INDUCTORS Coilcraft 847-639-6400 847-639-1469 www.coilcraft.com Coiltronics 561-241-7876 561-241-9339 www.coiltronics.com Sumida USA 847-956-0666 847-956-0702 www.sumida.com Toko 847-297-0070 847-699-1194 www.tokoam.com CAPACITORS AVX 803-946-0690 803-626-3123 www.avxcorp.com Kemet 408-986-0424 408-986-1442 www.kemet.
PAGE 12
MAX1836/MAX1837 24V Internal Switch, 100% Duty Cycle, Step-Down Converters INPUT 4.5V TO 24V CIN 10µF 25V L1 47µH IN OUTPUT 5V LX COUT 68µF 10V D1 SHDN INPUT 3.6V TO 18V CIN 10µF L1 47µH IN LX OUT SHDN MAX1836 MAX1837 MAX1837 GND FB GND COUT 100µF D1 OUT OUTPUT -3.3V OR -5V FB NOTE: HIGH-CURRENT PATHS SHOWN WITH BOLD LINES. CIN = TAIYO YUDEN TMK432BJ106KM L1 = SUMIDA CDRH5D28-470 COUT = SANYO POSCAP 10TPC68M D1 = NIHON EP05Q03L Figure 7.
PAGE 13
24V Internal Switch, 100% Duty Cycle, Step-Down Converters 6LSOT.EPS PACKAGE OUTLINE, SOT 6L BODY 21-0058 G 1 1 ______________________________________________________________________________________ 13 MAX1836/MAX1837 Package Information (The package drawing(s) in this data sheet may not reflect the most current specifications. For the latest package outline information, go to www.maxim-ic.com/packages.
PAGE 14
Package Information (continued) (The package drawing(s) in this data sheet may not reflect the most current specifications. For the latest package outline information, go to www.maxim-ic.com/packages.) 6, 8, &10L, DFN THIN.EPS MAX1836/MAX1837 24V Internal Switch, 100% Duty Cycle, Step-Down Converters PACKAGE OUTLINE, 6,8,10 & 14L, TDFN, EXPOSED PAD, 3x3x0.
PAGE 15
24V Internal Switch, 100% Duty Cycle, Step-Down Converters PACKAGE VARIATIONS COMMON DIMENSIONS SYMBOL MIN. MAX. PKG. CODE N D2 E2 e JEDEC SPEC b A 0.70 0.80 T633-1 6 1.50±0.10 2.30±0.10 0.95 BSC MO229 / WEEA 0.40±0.05 1.90 REF D 2.90 3.10 T633-2 6 1.50±0.10 2.30±0.10 0.95 BSC MO229 / WEEA 0.40±0.05 1.90 REF [(N/2)-1] x e E 2.90 3.10 T833-1 8 1.50±0.10 2.30±0.10 0.65 BSC MO229 / WEEC 0.30±0.05 1.95 REF A1 0.00 0.05 T833-2 8 1.50±0.10 2.30±0.10 0.