19-1919; Rev 2; 8/04
24V Internal Switch, 100% Duty Cycle,
Step-Down Converters
MAX1836/MAX1837
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
IN
. 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.
____________________________Features
♦
4.5V to 24V Input Voltage Range
♦
Preset 3.3V or 5V Output
♦
Adjustable Output from 1.25V to V
IN
♦
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
Ordering Information
PART
MAX1836ETT33-T
MAX1836ETT50-T
MAX1836EUT33-T
MAX1836EUT50-T
MAX1837ETT33-T
MAX1837ETT50-T
MAX1837EUT33-T
MAX1837EUT50-T
TEMP RANGE
-40°C to +85°C
-40°C to +85°C
-40°C to +85°C
-40°C to +85°C
-40°C to +85°C
-40°C to +85°C
-40°C to +85°C
-40°C to +85°C
PIN-
PACKAGE
6 TDFN-EP*
6 TDFN-EP*
6 SOT23-6
6 SOT23-6
6 TDFN-EP*
6 TDFN-EP*
6 SOT23-6
6 SOT23-6
TOP
MARK
AJG
AJE
AANY
AANW
AJH
AJF
AANZ
AANX
Applications
9V Battery Systems
Notebook Computers
Distributed Power Systems
Backup Supplies
4mA to 20mA Loop Power Supplies
Industrial Control Supplies
Hand-Held Devices
Selector Guide appears at end of data sheet.
Typical Operating Circuit
INPUT
4.5V TO 24V
OUTPUT
3.3V OR 5V
IN
SHDN
OUT
MAX1836
MAX1837
GND
FB
LX
Pin Configurations
TOP VIEW
FB
1
6
OUT
FB
1
GND
2
5
SHDN
IN
3
IN
3
4
LX
6
OUT
SHDN
LX
GND
2
MAX1836
MAX1837
MAX1836
MAX1837
5
4
TDFN
NOTE:
HIGH-CURRENT PATHS SHOWN WITH BOLD LINES.
SOT23
________________________________________________________________
Maxim Integrated Products
1
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.
24V Internal Switch, 100% Duty Cycle,
Step-Down Converters
MAX1836/MAX1837
ABSOLUTE MAXIMUM RATINGS
IN,
SHDN
to GND ...................................................-0.3V to +25V
LX to GND.......................................................-2V to (V
IN
+ 0.3V)
OUT, FB to GND.......................................................-0.3V to +6V
Continuous Power Dissipation (T
A
= +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) .........1951mW
Operating Temperature Range ...........................-40°C to +85°C
Junction Temperature ......................................................+150°C
Storage Temperature Range .............................-65°C to +150°C
Lead Temperature (soldering, 10s) .................................+300°C
Note 1:
Thermal properties are specified with product mounted on PC board with 1in
2
of copper area and still air.
Stresses beyond those listed under “Absolute Maximum Ratings” may cause permanent damage to the device. These are stress ratings only, and functional
operation of the device at these or any other conditions beyond those indicated in the operational sections of the specifications is not implied. Exposure to
absolute maximum rating conditions for extended periods may affect device reliability.
ELECTRICAL CHARACTERISTICS
(Circuits of Figures 1 (MAX1836) and 2 (MAX1837), V
IN
= 12V,
SHDN
= IN,
T
A
= 0°C to +85°C.
Typical values are at T
A
= +25°C,
unless otherwise noted.)
PARAMETER
Input Supply Range
Input Undervoltage Lockout
Threshold
Input Supply Current
Input Supply Current in Dropout
Input Shutdown Current
SYMBOL
V
IN
V
UVLO
I
IN
I
IN(DROP)
V
IN
= 5V
SHDN
= GND
FB = GND,
I
LOAD
= 0 to 125mA
(MAX1836) or
250mA (MAX1837)
(Note 2)
MAX183_EUT50,
MAX183_ETT50
MAX183_EUT33,
MAX183_ETT33
4.80
3.168
1.25
1.200
V
OUT
= 5V
I
FB
Threshold
t
OFF(MIN)
t
ON(MAX)
R
LX
I
LIM
V
FB
= 1.3V
V
IN
= 6V
MAX1836
MAX1837
250
500
-75
V
FB
= 0 or 1.25V, T
A
= +25°C
V
FB
rising or falling
-25
50
0.2
7
100
0.4
10
1.1
312
625
1.25
2.5
V
IN
rising
V
IN
falling
CONDITIONS
MIN
4.5
3.55
3.45
4.0
3.9
12
18
3
5.00
3.30
7
5.20
V
3.432
V
IN
1.300
7.4
+25
150
0.6
13
2
450
850
+75
V
V
µA
nA
mV
µs
µs
Ω
mA
mV
TYP
MAX
24
4.4
4.3
25
UNITS
V
V
µA
µA
µA
Output Voltage (Preset Mode)
V
OUT
Output Voltage Range
(Adjustable Mode)
Feedback Set Voltage
(Adjustable Mode)
OUT Bias Current
FB Bias Current
FB Dual Mode
TM
V
OUT
V
FB
LX Switch Minimum Off-Time
LX Switch Maximum On-Time
LX Switch On-Resistance
LX Current Limit
LX Zero-Crossing Threshold
Dual Mode is a trademark of Maxim Integrated Products, Inc.
2
_______________________________________________________________________________________
24V Internal Switch, 100% Duty Cycle,
Step-Down Converters
ELECTRICAL CHARACTERISTICS (continued)
(Circuits of Figures 1 (MAX1836) and 2 (MAX1837), V
IN
= 12V,
SHDN
= IN,
T
A
= 0°C to +85°C.
Typical values are at T
A
= +25°C,
unless otherwise noted.)
PARAMETER
Zero-Crossing Timeout
LX Switch Leakage Current
Dropout Voltage
Line Regulation
Load Regulation
Shutdown Input Threshold
Shutdown Leakage Current
Thermal Shutdown
V
SHDN
I
SHDN
V
DROPOUT
SYMBOL
CONDITIONS
LX does not rise above the threshold
V
IN
= 18V, LX = GND, T
A
= +25°C
I
OUT
= 100mA, V
IN
= 5V
V
IN
= 5V to 24V
I
OUT
= 0 to 125mA (MAX1836) or 250mA
(MAX1837)
V
IN
= 4.5V to 24V (Note 3)
V
SHDN
= 0 or 24V
10°C hysteresis (typ)
0.8
-1
160
120
0.05
0.3
2.4
+1
MIN
TYP
30
1
MAX
UNITS
µs
µA
mV
%
%
V
µA
°C
MAX1836/MAX1837
ELECTRICAL CHARACTERISTICS
(Circuits of Figures 1 (MAX1836) and 2 (MAX1837), V
IN
= 12V,
SHDN
= IN,
T
A
= -40°C to +85°C,
unless otherwise noted.) (Note 4)
PARAMETER
Input Supply Range
Input Undervoltage Lockout
Threshold
Input Supply Current
Input Shutdown Current
SYMBOL
V
IN
V
UVLO
I
IN
SHDN
= GND
FB = GND,
I
LOAD
= 0 to 125mA
(MAX1836) or
250mA (MAX1837)
(Note 2)
MAX183_EUT50,
MAX183_ETT50
MAX183_EUT33,
MAX183_ETT33
4.80
3.168
1.25
1.200
V
OUT
= 5V
V
FB
rising or falling
t
OFF(MIN)
t
ON(MAX)
R
LX
I
LIM
V
FB
= 1.3V
V
IN
= 6V
MAX1836
MAX1837
250
500
50
0.2
7
V
IN
rising
V
IN
falling
CONDITIONS
MIN
4.5
3.55
3.45
TYP
MAX
24
4.4
4.3
25
7
5.20
V
3.432
V
IN
1.300
7.4
150
0.6
13
2
450
900
V
V
µA
mV
µs
µs
Ω
mA
UNITS
V
V
µA
µA
Output Voltage (Preset Mode)
V
OUT
Output Voltage Range
(Adjustable Mode)
Feedback Set Voltage
(Adjustable Mode)
OUT Bias Current
FB Dual Mode Threshold
LX Switch Minimum Off-Time
LX Switch Maximum On-Time
LX Switch On-Resistance
LX Current Limit
V
OUT
V
FB
_______________________________________________________________________________________
3
24V Internal Switch, 100% Duty Cycle,
Step-Down Converters
MAX1836/MAX1837
ELECTRICAL CHARACTERISTICS (continued)
(Circuits of Figures 1 (MAX1836) and 2 (MAX1837), V
IN
= 12V,
SHDN
= IN,
T
A
= -40°C to +85°C,
unless otherwise noted.) (Note 4)
PARAMETER
LX Zero-Crossing Threshold
Shutdown Input Threshold
Shutdown Leakage Current
V
SHDN
I
SHDN
V
IN
= 4.5V to 24V (Note 3)
V
SHDN
= 0 or 24V
SYMBOL
CONDITIONS
MIN
-75
0.8
-1
TYP
MAX
+75
2.4
+1
UNITS
mV
V
µA
Note 2:
When using the shutdown input, the maximum output voltage allowed with external feedback is 5.5V. If the output voltage is
set above 5.5V, connect shutdown to the input.
Note 3:
Shutdown input minimum slew rate (rising or falling) is 10V/ms.
Note 4:
Specifications to -40°C are guaranteed by design, not production tested.
Typical Operating Characteristics
(Circuits of Figures 1 (MAX1836) and 2 (MAX1837), V
IN
= 12V,
SHDN
= IN, T
A
= +25°C.)
MAX1836EUT33
OUTPUT VOLTAGE vs. LOAD CURRENT
MAX1836/7 toc01
MAX1836EUT33
EFFICIENCY vs. LOAD CURRENT
MAX1836/7 toc02
MAX1837EUT33
OUTPUT VOLTAGE vs. LOAD CURRENT
FIGURE 2
3.32
OUTPUT VOLTAGE (V)
3.31
V
IN
= 9V
3.30
3.29
3.28
3.27
V
IN
= 5V
V
IN
= 12V
MAX1836/7 toc03
3.33
FIGURE 1
3.32
OUTPUT VOLTAGE (V)
3.31
3.30
3.29
3.28
3.27
0
50
100
150
V
IN
= 9V to 12V
V
IN
= 5V
100
95
EFFICIENCY (%)
90
85
80
V
IN
= 12V
75
70
FIGURE 1
V
OUT
= 3.3V
V
IN
= 5V
V
IN
= 9V
3.33
200
0.1
1
10
100
1000
0
50
100
150
200
250
300
350
LOAD CURRENT (mA)
LOAD CURRENT (mA)
LOAD CURRENT (mA)
MAX1837EUT33
EFFICIENCY vs. LOAD CURRENT
MAX1836/7 toc04
MAX1837EUT33
SWITCHING FREQUENCY vs. LOAD CURRENT
MAX1836/7 toc05
MAX1837EUT33
OUTPUT VOLTAGE vs. INPUT VOLTAGE
I
OUT
= 10mA
3.32
OUTPUT VOLTAGE (V)
3.31
3.30
3.29
3.28
3.27
FIGURE 2
V
OUT
= 3.3V
L1 = 47µH
0
4
8
12
16
20
24
MAX1836/7 toc06
100
95
EFFICIENCY (%)
90
85
80
75
70
0.1
1
10
V
IN
= 12V
100
FIGURE 2
V
OUT
= 3.3V
180
160
140
FREQUENCY (kHz)
120
100
80
60
40
20
0
V
IN
= 5V
0
50
100
150
200
250
300
V
IN
= 12V
FIGURE 2
V
OUT
= 3.3V
V
IN
= 9V
3.33
V
IN
= 5V
V
IN
= 9V
I
OUT
= 200mA
1000
350
LOAD CURRENT (mA)
LOAD CURRENT (mA)
INPUT VOLTAGE (V)
4
_______________________________________________________________________________________
24V Internal Switch, 100% Duty Cycle,
Step-Down Converters
MAX1836/MAX1837
Typical Operating Characteristics (continued)
(Circuits of Figures 1 (MAX1836) and 2 (MAX1837), V
IN
= 12V,
SHDN
= IN, T
A
= +25°C.)
MAX1837EUT33
EFFICIENCY vs. INPUT VOLTAGE
MAX1836/7 toc07
MAX1837EUT33
SWITCHING FREQUENCY vs. INPUT VOLTAGE
MAX1836/7 toc08
MAX1837EUT33
PEAK INDUCTOR CURRENT vs. INPUT VOLTAGE
FIGURE 2
V
OUT
= 3.3V
L1 = 47µH
MAX1836/7 toc09
100
95
EFFICIENCY (%)
90
85
80
75
70
0
4
8
12
16
20
I
OUT
= 10mA
I
OUT
= 200mA
FIGURE 2
V
OUT
= 3.3V
L1 = 47µH
100
I
OUT
= 200mA
1000
PEAK INDUCTOR CURRENT (mA)
I
OUT
= 200mA
I
OUT
= 10mA
600
800
FREQUENCY (kHz)
10
FIGURE 2
V
OUT
= 3.3V
L1 = 47µH
400
I
OUT
= 10mA
1
24
0
4
8
12
16
20
24
200
0
0
LIMITED BY
t
ON(MIN)
LIMITED BY
I
LIM
4
8
12
16
20
24
INPUT VOLTAGE (V)
INPUT VOLTAGE (V)
INPUT VOLTAGE (V)
MAX1837EUT50
OUTPUT VOLTAGE vs. LOAD CURRENT
MAX1836/7 toc10
MAX1837EUT50
EFFICIENCY vs. LOAD CURRENT
FIGURE 6
V
OUT
= 5V
V
IN
= 9V
EFFICIENCY (%)
90
85
80
75
V
IN
= 18V
V
IN
= 24V
V
IN
= 12V
MAX1836/7 toc11
5.04
V
IN
= 12V TO 24V
OUTPUT VOLTAGE (V)
5.02
V
IN
= 9V
100
95
V
IN
= 7V
5.00
4.98
V
IN
= 7V
4.96
0
FIGURE 6
70
50
100
150
200
250
300
0.1
1
10
100
1000
LOAD CURRENT (mA)
LOAD CURRENT (mA)
MAX1837EUT50
DROPOUT VOLTAGE vs. LOAD CURRENT
MAX1836/7 toc12
NO-LOAD SUPPLY CURRENT
vs. INPUT VOLTAGE
MAX1836/7 toc13
400
350
DROPOUT VOLTAGE (mV)
300
250
200
150
100
50
0
0
FIGURE 6
V
OUT
= 5V
15
14
SUPPLY CURRENT (µA)
13
12
11
10
100
200
300
0
4
8
12
16
20
24
LOAD CURRENT (mA)
INPUT VOLTAGE (V)
_______________________________________________________________________________________
5
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