MAX1836ETT33+T [MAXIM]
Switching Regulator, 0.45A, BICMOS, PDSO6, 3 X 3 MM, 0.80 MM HEIGHT, LEAD FREE, MO-229WEEA, TDFN-6;
| 型号： | MAX1836ETT33+T |
| 厂家： | 
MAXIM INTEGRATED PRODUCTS |
| 描述： | Switching Regulator, 0.45A, BICMOS, PDSO6, 3 X 3 MM, 0.80 MM HEIGHT, LEAD FREE, MO-229WEEA, TDFN-6 信息通信管理 开关 光电二极管 |
| 文件： | 总15页 (文件大小：1963K) |
| 中文： | 中文翻译 | 下载： | 下载PDF数据表文档文件 |
EVALUATION KIT AVAILABLE
MAX1836/MAX1837
24V Internal Switch, 100% Duty Cycle,
Step-Down Converters
General Description
Features
● 4.5V to 24V Input Voltage Range
The MAX1836/MAX1837 high-efficiency step-down con-
verters provide a preset 3.3V or 5V output voltage from
supply voltages as high as 24V. Using external feedback
resistors, the output voltage can be adjusted from 1.25V
● Preset 3.3V or 5V Output
● Adjustable Output from 1.25V to V
IN
● Output Currents Up to 125mA (MAX1836) or
to V . An internal current-limited switching MOSFET
delivers load currents up to 125mA (MAX1836) or 250mA
(MAX1837).
IN
250mA (MAX1837)
● Efficiency Over 90%
The unique current-limited control scheme, operating
with duty cycles up to 100%, minimizes the dropout volt-
age (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.
● 12μA Quiescent Current
● 3μA Shutdown Current
● 100% Maximum Duty Cycle for Low Dropout
● Small 6-Pin SOT23 and TDFN Packages
The MAX1836/MAX1837 step-down converters with inter-
nal switching MOSFETs are available in 6-pin SOT23
and 3mm x 3mm TDFN packages, making them ideal
for low-cost, low-power, space-sensitive applications.
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 currents, use the
MAX1626/MAX1627 step-down controllers that drive an
external P-channel MOSFET to deliver up to 20W.
Ordering Information
PIN-
PACKAGE
TOP
PART
TEMP RANGE
MARK
MAX1836ETT33-T -40°C to +85°C 6 TDFN-EP*
MAX1836ETT50-T -40°C to +85°C 6 TDFN-EP*
MAX1836EUT33-T -40°C to +85°C 6 SOT23
MAX1836EUT50-T -40°C to +85°C 6 SOT23
MAX1837ETT33-T -40°C to +85°C 6 TDFN-EP*
MAX1837ETT50-T -40°C to +85°C 6 TDFN-EP*
MAX1837EUT33-T -40°C to +85°C 6 SOT23
MAX1837EUT50-T -40°C to +85°C 6 SOT23
*EP = Exposed pad.
AJG
AJE
AANY
AANW
AJH
Applications
● 9V Battery Systems
AJF
AANZ
AANX
● Notebook Computers
● Distributed Power Systems
● Backup Supplies
● 4mA to 20mA Loop Power Supplies
● Industrial Control Supplies
● Handheld Devices
T = Tape and reel.
Selector Guide appears at end of data sheet.
Typical Operating Circuit
Pin Configurations
OUTPUT
3.3V OR 5V
INPUT
4.5V TO 24V
TOP VIEW
IN
LX
OUT
FB
FB
GND
IN
1
2
3
6
5
4
OUT
SHDN
LX
FB
GND
IN
1
2
3
6
5
4
OUT
SHDN
LX
SHDN
MAX1836
MAX1837
MAX1836
MAX1837
MAX1836
MAX1837
GND
TDFN
SOT23
NOTE: HIGH-CURRENT PATHS SHOWN WITH BOLD LINES.
19-1919; Rev 3; 7/06
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 (V + 0.3V)
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
IN
OUT, FB to GND.......................................................-0.3V to +6V
Continuous Power Dissipation (T = +70°C) (Note 1)
A
6-Pin SOT23 (derate 8.7mW/°C above +70°C)...........696mW
6-Pin TDFN (derate 24.4mW/°C above +70°C).........1951mW
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.
2
Note 1: Thermal properties are specified with product mounted on PC board with 1in of copper area and still air.
Electrical Characteristics
(Circuits of Figures 1 (MAX1836) and 2 (MAX1837), V = 12V, SHDN = IN, T = 0°C to +85°C. Typical values are at T = +25°C,
IN
A
A
unless otherwise noted.)
PARAMETER
SYMBOL
CONDITIONS
MIN
4.5
TYP
MAX
24
UNITS
Input Supply Range
V
V
IN
V
V
rising
falling
3.55
3.45
4.0
3.9
12
18
3
4.4
4.3
25
Input Undervoltage Lockout
Threshold
IN
V
V
UVLO
IN
Input Supply Current
I
µA
µA
µA
IN
Input Supply Current in Dropout
Input Shutdown Current
I
V
= 5V
IN(DROP)
IN
SHDN = GND
7
MAX183_EUT50,
MAX183_ETT50
FB = GND,
4.80
3.168
1.25
5.00
3.30
5.20
I
= 0 to 125mA
LOAD
Output Voltage (Preset Mode)
V
V
V
OUT
(MAX1836) or
250mA (MAX1837)
MAX183_EUT33,
MAX183_ETT33
3.432
Output Voltage Range
(Adjustable Mode)
(Note 2)
V
V
V
OUT
IN
Feedback Set Voltage
(Adjustable Mode)
V
1.200
1.25
2.5
1.300
FB
OUT Bias Current
V
V
V
= 5V
7.4
+25
150
0.6
13
µA
nA
mV
µs
µs
Ω
OUT
FB Bias Current
I
= 0 or 1.25V, T = +25°C
A
-25
50
0.2
7
FB
FB
FB
FB Dual ModeTM Threshold
LX Switch Minimum Off-Time
LX Switch Maximum On-Time
LX Switch On-Resistance
rising or falling
100
0.4
10
t
OFF(MIN)
t
V
V
= 1.3V
= 6V
ON(MAX)
FB
R
1.1
312
625
2
LX
IN
MAX1836
MAX1837
250
500
-75
450
850
+75
LX Current Limit
I
mA
mV
LIM
LX Zero-Crossing Threshold
Dual Mode is a trademark of Maxim Integrated Products, Inc.
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MAX1836/MAX1837
24V Internal Switch, 100% Duty Cycle,
Step-Down Converters
Electrical Characteristics (continued)
(Circuits of Figures 1 (MAX1836) and 2 (MAX1837), V = 12V, SHDN = IN, T = 0°C to +85°C. Typical values are at T = +25°C,
IN
A
A
unless otherwise noted.)
PARAMETER
Zero-Crossing Timeout
LX Switch Leakage Current
Dropout Voltage
SYMBOL
CONDITIONS
LX does not rise above the threshold
MIN
TYP
MAX
UNITS
µs
30
V
= 18V, LX = GND, T = +25°C
1
µA
IN
A
V
I
= 100mA, V = 5V
IN
120
mV
%
DROPOUT
OUT
Line Regulation
V
= 5V to 24V
0.05
IN
I
= 0 to 125mA (MAX1836) or 250mA
OUT
Load Regulation
0.3
%
(MAX1837)
Shutdown Input Threshold
Shutdown Leakage Current
Thermal Shutdown
V
V
V
= 4.5V to 24V (Note 3)
0.8
-1
2.4
+1
V
SHDN
IN
I
= 0 or 24V
µA
°C
SHDN
SHDN
10°C hysteresis (typ)
160
Electrical Characteristics
(Circuits of Figures 1 (MAX1836) and 2 (MAX1837), V = 12V, SHDN = IN, T = -40°C to +85°C, unless otherwise noted.) (Note 4)
IN
A
PARAMETER
SYMBOL
CONDITIONS
MIN
4.5
TYP
MAX
24
UNITS
Input Supply Range
V
V
IN
V
V
rising
falling
3.55
3.45
4.4
4.3
25
Input Undervoltage Lockout
Threshold
IN
V
V
UVLO
IN
Input Supply Current
I
µA
µA
IN
Input Shutdown Current
SHDN = GND
7
MAX183_EUT50,
MAX183_ETT50
FB = GND,
4.80
3.168
1.25
5.20
I
= 0 to 125mA
LOAD
Output Voltage (Preset Mode)
V
V
OUT
(MAX1836) or
250mA (MAX1837)
MAX183_EUT33,
MAX183_ETT33
3.432
Output Voltage Range
(Adjustable Mode)
V
(Note 2)
V
V
V
OUT
IN
Feedback Set Voltage
(Adjustable Mode)
V
1.200
1.300
FB
OUT Bias Current
V
V
= 5V
7.4
150
0.6
13
µA
mV
µs
µs
Ω
OUT
FB Dual Mode Threshold
LX Switch Minimum Off-Time
LX Switch Maximum On-Time
LX Switch On-Resistance
rising or falling
50
0.2
7
FB
t
OFF(MIN)
t
V
V
= 1.3V
= 6V
ON(MAX)
FB
R
2
LX
IN
MAX1836
MAX1837
250
500
450
900
LX Current Limit
I
mA
LIM
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MAX1836/MAX1837
24V Internal Switch, 100% Duty Cycle,
Step-Down Converters
Electrical Characteristics (continued)
(Circuits of Figures 1 (MAX1836) and 2 (MAX1837), V = 12V, SHDN = IN, T = -40°C to +85°C, unless otherwise noted.) (Note 4)
IN
A
PARAMETER
SYMBOL
CONDITIONS
MIN
-75
0.8
-1
TYP
MAX
+75
2.4
UNITS
mV
V
LX Zero-Crossing Threshold
Shutdown Input Threshold
Shutdown Leakage Current
V
V
V
= 4.5V to 24V (Note 3)
SHDN
IN
I
= 0 or 24V
+1
µA
SHDN
SHDN
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 = 12V, SHDN = IN, T = +25°C.)
IN
A
MAX1836EUT33
OUTPUT VOLTAGE vs. LOAD CURRENT
MAX1836EUT33
EFFICIENCY vs. LOAD CURRENT
MAX1837EUT33
OUTPUT VOLTAGE vs. LOAD CURRENT
100
95
3.33
3.32
3.31
3.30
3.29
3.28
3.27
3.33
3.32
3.31
3.30
3.29
3.28
3.27
FIGURE 1
= 3.3V
FIGURE 2
FIGURE 1
V
OUT
V
= 5V
IN
V
IN
= 5V
V
= 9V
IN
90
85
80
V
IN
= 5V
V
IN
= 9V
V
= 12V
IN
V
IN
= 9V to 12V
V
IN
= 12V
100
75
70
0
50
100
150
200
0.1
1
10
1000
0
50 100 150 200 250 300 350
LOAD CURRENT (mA)
LOAD CURRENT (mA)
LOAD CURRENT (mA)
MAX1837EUT33
SWITCHING FREQUENCY vs. LOAD CURRENT
MAX1837EUT33
OUTPUT VOLTAGE vs. INPUT VOLTAGE
MAX1837EUT33
EFFICIENCY vs. LOAD CURRENT
100
95
3.33
3.32
3.31
3.30
3.29
3.28
3.27
180
FIGURE 2
= 3.3V
FIGURE 2
= 3.3V
I
= 10mA
OUT
160
140
120
100
80
V
OUT
V
OUT
V
IN
= 9V
V
IN
= 12V
V
= 5V
IN
90
85
80
I
= 200mA
OUT
V
= 9V
IN
60
40
FIGURE 2
= 3.3V
L1 = 47µH
75
70
V
IN
= 5V
20
V
OUT
V
IN
= 12V
100
0
0.1
1
10
1000
0
50 100 150 200 250 300 350
LOAD CURRENT (mA)
0
4
8
12
16
20
24
LOAD CURRENT (mA)
INPUT VOLTAGE (V)
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MAX1836/MAX1837
24V Internal Switch, 100% Duty Cycle,
Step-Down Converters
Typical Operating Characteristics (continued)
(Circuits of Figures 1 (MAX1836) and 2 (MAX1837), V = 12V, SHDN = IN, T = +25°C.)
IN
A
MAX1837EUT33
PEAK INDUCTOR CURRENT vs. INPUT VOLTAGE
MAX1837EUT33
SWITCHING FREQUENCY vs. INPUT VOLTAGE
MAX1837EUT33
EFFICIENCY vs. INPUT VOLTAGE
100
1000
100
95
90
85
80
75
70
FIGURE 2
= 3.3V
L1 = 47µH
I
= 200mA
FIGURE 2
OUT
V
OUT
V
= 3.3V
OUT
I
= 200mA
OUT
L1 = 47µH
800
I
= 10mA
OUT
600
400
FIGURE 2
= 3.3V
10
V
OUT
I
= 200mA
OUT
L1 = 47µH
I
= 10mA
12
200
0
OUT
I
= 10mA
20
OUT
LIMITED BY
LIMITED BY
t
I
ON(MIN)
LIM
1
0
4
8
12
16
24
0
4
8
12
16
20
24
0
4
8
16
20
24
INPUT VOLTAGE (V)
INPUT VOLTAGE (V)
INPUT VOLTAGE (V)
MAX1837EUT50
OUTPUT VOLTAGE vs. LOAD CURRENT
MAX1837EUT50
EFFICIENCY vs. LOAD CURRENT
5.04
5.02
5.00
4.98
100
95
FIGURE 6
V
= 12V TO 24V
IN
V
OUT
= 5V
V
= 9V
V
= 7V
IN
IN
V
= 9V
IN
V
IN
= 12V
90
85
80
V
= 7V
IN
V
= 24V
IN
75
70
V
= 18V
10
IN
FIGURE 6
50
4.96
0.1
1
100
1000
0
100
150
200
250
300
LOAD CURRENT (mA)
LOAD CURRENT (mA)
NO-LOAD SUPPLY CURRENT
vs. INPUT VOLTAGE
MAX1837EUT50
DROPOUT VOLTAGE vs. LOAD CURRENT
15
14
13
12
11
10
400
350
300
250
200
150
100
FIGURE 6
V
OUT
= 5V
50
0
0
100
200
300
0
4
8
12
16
20
24
LOAD CURRENT (mA)
INPUT VOLTAGE (V)
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MAX1836/MAX1837
24V Internal Switch, 100% Duty Cycle,
Step-Down Converters
Typical Operating Characteristics (continued)
(Circuits of Figures 1 (MAX1836) and 2 (MAX1837), V = 12V, SHDN = IN, T = +25°C.)
IN
A
MAX1837EUT50
LOAD TRANSIENT
MAX1837EUT50
LINE TRANSIENT
MAX1836/7 toc14
MAX1836/7 toc15
400mA
20V
10V
A
200mA
0
A
0
5.1V
5.0V
5.02V
5.00V
4.98V
B
C
B
C
4.9V
500mA
0
750mA
250mA
0
100µs/div
400µs/div
A: I
B: V
= 10mA to 250mA, 200mA/div
= 5V, 20mV/div
A: V = 9V to 18V, 10V/div
OUT
IN
B: V
= 5V, R
= 100Ω, 100mV/div
OUT
OUT
OUT
C: I , 500mA/div
L
C: I , 500mA/div
L
V
= 12V, FIGURE 6
FIGURE 6
IN
MAX1837EUT50
STARTUP WAVEFORM
MAX1837EUT50
LINE TRANSIENT NEAR DROPOUT
MAX1836/7 toc17
MAX1836/7 toc16
15V
10V
2V
A
A
B
0
5V
5.1V
5.0V
4V
2V
B
C
0
500mA
0
4.9V
500mA
0
C
200µs/div
= 0 to 2V, 2V/div
400µs/div
A: V = 5V to 12V, 5V/div
A: V
B: V
SHDN
OUT
IN
= 5V, R
= 100Ω, 2V/div
B: V
= 5V, R
= 100Ω, 100mV/div
OUT
OUT
OUT
C: I , 500mA/div
L
C: I , 500mA/div
L
V
= 12V, FIGURE 6
FIGURE 6
IN
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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_
EUT50) output. Connect to a resistive divider between the output and FB to adjust the output voltage between
1
FB
1.25V and V , and connect the OUT pin to GND. When setting output voltages above 5.5V, permanently
IN
connect SHDN to IN.
2
3
4
GND
IN
Ground
Input Voltage. 4.5V to 24V input range. Connected to the internal p-channel power MOSFET’s source.
Inductor Connection. Connected to the internal p-channel power MOSFET’s drain.
LX
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.
5
SHDN
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.
6
OUT
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.
—
L1
47µH
L1
22µH
OUTPUT
3.3V OR 5V
OUTPUT
3.3V OR 5V
INPUT
4.5V OR 12V
INPUT
4.5V OR 12V
IN
LX
IN
LX
C
C
OUT
150µF
6.3V
C
10µF
25V
OUT
C
10µF
25V
IN
IN
D1
D1
SHDN
MAX1836
SHDN
100µF
6.3V
MAX1837
OUT
OUT
GND
FB
GND
FB
C
= TAIYO YUDEN TMK432BJ106KM
C = TAIYO YUDEN TMK432BJ106KM
IN
IN
L1 = SUMIDA CDRH5D28-470
= SANYO POSCAP 6TPC100M (SMALLER CAPACITORS CAN BE USED FOR 5V)
L1 = SUMIDA CDRH5D28-220
C = SANYO OS-CON 6SA150M (SMALLER CAPACITORS CAN BE USED FOR 5V)
OUT
C
OUT
D1 = NIHON EP05Q03L
D1 = NIHON ED05Q03L
NOTE: HIGH-CURRENT PATHS SHOWN WITH BOLD LINES.
NOTE: HIGH-CURRENT PATHS SHOWN WITH BOLD LINES.
Figure 1. Typical MAX1836 Application Circuit
Figure 2. Typical MAX1837 Application Circuit
high switching frequency minimize PC board space and
component cost.
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
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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MAX1836/MAX1837
24V Internal Switch, 100% Duty Cycle,
Step-Down Converters
OUTPUT
3.3V OR 5V
INPUT
4.5V OR 24V
L1
LX
IN
C
IN
SHDN
D1
C
OUT
V
SENSE
OUT
FB
R
S
Q
MAXIMUM
OFF-TIME
DELAY
Q
TRIG
100mV
V
SET
1.25V
Q
TRIG
MAXIMUM
ON-TIME
DELAY
MAX1836
MAX1837
GND
Figure 3. Functional Diagram
When the output voltage is too low, an error compara-
tor sets a flip-flop, which turns on the internal p-channel
MOSFET and begins a switching cycle (Figure 3). As
shown in Figure 4, the inductor current ramps up linearly,
charging the output capacitor and servicing the load. The
MOSFET turns off when the current limit is reached, or
when the maximum on-time is exceeded while the output
voltage is in regulation. Otherwise, the MOSFET remains
on, allowing a duty cycle up to 100% to ensure the lowest
possible dropout voltage. Once the MOSFET turns off, the
flip-flop resets, diode D1 turns on, and the current through
the inductor ramps back down, transferring the stored
energy to the output capacitor and load. The MOSFET
remains off until the 0.5μs minimum off-time expires and
the inductor current ramps down to zero, and the output
voltage drops back below the set point.
10V
A
0
B
3.3V
500mA
0
C
4µs/div
CIRCUIT OF FIGURE 2, V = 12V
IN
A. V , 5V/div
LX
B. V
= 3.3V, 20mV/div, 200mA LOAD
OUT
C. INDUCTOR CURRENT, 500mA/div
Figure 4. Discontinuous-Conduction Operation
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MAX1836/MAX1837
24V Internal Switch, 100% Duty Cycle,
Step-Down Converters
the Selector Guide. For example, the MAX1836EUT33
has a preset 3.3V output voltage.
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.
The MAX1836/MAX1837 output voltage may be adjusted
by connecting a voltage divider from the output to FB
(Figure 5). When externally adjusting the output voltage,
connect OUT to GND. Select R2 in the 10kΩ to 100kΩ
range. Calculate R1 with the following equation:
V
OUT
R1 = R2
−1
V
FB
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 con-
verter with 100% duty cycle, the dropout voltage depends
where V = 1.25V, and V
may range from 1.25V to
FB
OUT
V . When setting output voltages above 5.5V, the shut-
IN
down feature cannot be used, so SHDN must be perma-
nently connected to IN.
on the MOSFET drain-to-source on-resistance (R
)
DS(ON)
and inductor series resistance; therefore, it is proportional
to the load current:
Inductor Selection
When selecting the inductor, consider these four param-
eters: inductance value, saturation current rating, series
resistance, and size. The MAX1836/MAX1837 operate
with a wide range of inductance values. For most applica-
tions, values between 10μH and 100μH work best with
the controller’s switching frequency. Calculate the mini-
mum inductance value as follows:
V
= I
× R
+ R
DS(ON) INDUCTOR
DROPOUT
OUT
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 internal
P-channel 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.
Do not leave SHDN floating. If unused, connect SHDN to
IN. When setting output voltages above 5.5V, the shut-
down feature cannot be used, so SHDN must be perma-
nently connected to IN. The SHDN input voltage slew rate
must be greater than 10V/ms.
V
− V
t
(
)
IN(MAX)
OUT ON(MIN)
L
=
(MIN)
I
LIM
where t
= 1.0μs. Inductor values up to six times
ON(MIN)
L
are acceptable. Low-value inductors may be small-
(MIN)
er in physical size and less expensive, but they result in
higher peak-current overshoot due to current-sense com-
parator propagation delay (300ns). Peak-current over-
shoot reduces efficiency and could exceed the current
ratings of the internal switching MOSFET and external
components.
Thermal-Overload Protection
Thermal-overload protection limits total power dissipa-
tion in the MAX1836/MAX1837. When the junction tem-
OUTPUT
1.25V TO V
INPUT
4.5V OR 24V
perature exceeds T = +160°C, a thermal sensor turns off
L1
J
IN
IN
LX
the pass transistor, allowing the IC to cool. The thermal
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.
C
IN
D1
C
OUT
SHDN
R1
R2
FB
MAX1836
MAX1837
Design Information
GND
OUT
Output Voltage Selection
The feedback input features dual-mode operation.
Connect the output to OUT and FB to GND for the preset
output voltage. The MAX1836/MAX1837 are supplied
with factory-set output voltages of 3.3V or 5V. The two-
digit part number suffix identifies the output voltage. See
NOTE: HIGH-CURRENT PATHS SHOWN WITH BOLD LINES.
Figure 5. Adjustable Output Voltage
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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:
capacitor selection, but final values should be set by test-
ing a prototype or evaluation circuit. As a general rule, a
smaller amount of charge delivered in each pulse results
in less output ripple. Since the amount of charge deliv-
ered in each oscillator pulse is determined by the inductor
value and input voltage, the voltage ripple increases with
larger inductance but decreases with lower input voltages.
V
− V
300ns
(
+
LIM
)
IN
OUT
L
I
= I
PEAK
With low-cost aluminum electrolytic capacitors, the ESR-
induced ripple can be larger than that caused by the
current into and out of the capacitor. Consequently, high-
quality low-ESR aluminum-electrolytic, tantalum, polymer,
or ceramic filter capacitors are required to minimize out-
put ripple. Best results at reasonable cost are typically
achieved with an aluminum-electrolytic capacitor in the
100μF range, in parallel with a 0.1μF ceramic capacitor.
where the switch current-limit (I ) is typically 312mA
LIM
(MAX1836) or 625mA (MAX1837). Saturation occurs
when the inductor’s magnetic flux density reaches the
maximum level the core can support, and the inductance
starts to fall.
Inductor series resistance affects both efficiency and
dropout voltage. See the Input-Output (Dropout) Voltage
section. High series resistance limits the maximum current
available at lower input voltages and increases the drop-
out voltage. For optimum performance, select an inductor
with the lowest possible DC resistance that fits in the
allotted dimensions. Typically, the inductor’s series resis-
tance should be significantly less than that of the internal
P-channel MOSFET’s on-resistance (1.1Ω typ). Inductors
with a ferrite core, or equivalent, are recommended.
Input Capacitor
The input filter capacitor reduces peak currents drawn
from the power source and reduces noise and voltage
ripple on the input caused by the circuit’s switching. The
input capacitor must meet the ripple-current requirement
(I
) imposed by the switching currents defined by the
RMS
following equation:
The maximum output current of the MAX1836/MAX1837
current-limited converter is limited by the peak inductor
current. For the typical application, the maximum output
current is approximately:
V
V
− V
(
)
OUT IN OUT
I
= I
LOAD
RMS
V
IN
For most applications, nontantalum chemistries (ceramic,
aluminum, polymer, or OS-CON) are preferred due to
their robustness with high inrush currents typical of sys-
tems with low-impedance battery inputs. Alternatively,
two (or more) smaller-value low-ESR capacitors can be
connected in parallel for lower cost. Choose an input
capacitor that exhibits < +10°C temperature rise at the
RMS input current for optimal circuit longevity.
I
I
PEAK
OUT(MAX)
Output Capacitor
Choose the output capacitor to supply the maximum load
current with acceptable voltage ripple. The output ripple
has two components: variations in the charge stored in
the output capacitor with each LX pulse, and the voltage
drop across the capacitor’s equivalent series resistance
(ESR) caused by the current into and out of the capacitor:
Diode Selection
The current in the external diode (D1) changes abruptly
from zero to its peak value each time the LX switch turns
off. To avoid excessive losses, the diode must have a
fast turn-on time and a low forward voltage. Use a diode
with an RMS current rating of 0.5A or greater, and with a
V
≈ V
+ V
RIPPLE
RIPPLE(ESR) RIPPLE(C)
The output voltage ripple as a consequence of the ESR
and output capacitance is:
breakdown voltage > V . Schottky diodes are preferred.
IN
For high-temperature applications, Schottky diodes may
be inadequate due to their high leakage currents. In
such cases, ultra-high-speed silicon rectifiers are recom-
mended, although a Schottky diode with a higher reverse
voltage rating can often provide acceptable performance.
V
= I
ESR
RIPPLE(ESR)
PEAK
2
L I
(
−I
)
V
IN
PEAK
OUT
V
=
RIPPLE(C)
2C
V
V
− V
OUT OUT
IN OUT
where I
is the peak inductor current. See the Inductor
PEAK
Selection section. These equations are suitable for initial
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MAX1836/MAX1837
24V Internal Switch, 100% Duty Cycle,
Step-Down Converters
Table 1. Component Suppliers
SUPPLIER
PHONE
FAX
WEBSITE
INDUCTORS
Coilcraft
847-639-6400
561-241-7876
847-956-0666
847-297-0070
847-639-1469
561-241-9339
847-956-0702
847-699-1194
www.coilcraft.com
www.coiltronics.com
www.sumida.com
www.tokoam.com
Coiltronics
Sumida USA
Toko
CAPACITORS
AVX
803-946-0690
408-986-0424
847-468-5624
619-661-6835
408-573-4150
803-626-3123
408-986-1442
847-468-5815
619-661-1055
408-573-4159
www.avxcorp.com
www.kemet.com
www.panasonic.com
www.secc.co.jp
Kemet
Panasonic
Sanyo
Taiyo Yuden
DIODES
www.t-yuden.com
Central Semiconductor
International Rectifier
Nihon
516-435-1110
310-322-3331
847-843-7500
602-303-5454
516-543-7100
516-435-1824
310-322-3332
847-843-2798
602-994-6430
516-864-7630
www.centralsemi.com
www.irf.com
www.niec.co.jp
On Semiconductor
Zetex
www.onsemi.com
www.zetex.com
coupling. The MAX1837 evaluation kit shows the recom-
mended layout.
MAX1836/MAX1837 Stability
Commonly, instability is caused by excessive noise on the
feedback signal or ground due to poor layout or improper
component selection. When seen, instability typically
manifests itself as “motorboating,” which is characterized
by grouped switching pulses with large gaps and exces-
sive low-frequency output ripple during no-load or light-
load conditions.
Applications Information
High-Voltage Step-Down Converter
The typical application circuits’ (Figure 1 and Figure 2)
components were selected for 9V battery applications.
However, the MAX1836/MAX1837 input voltage range
allows supply voltages up to 24V. Figure 6 shows a modi-
fied application circuit for high-voltage applications. When
using higher input voltages, verify that the input capaci-
PC Board Layout and Grounding
High switching frequencies and large peak currents make
PC board layout an important part of the design. Poor lay-
out may introduce switching noise into the feedback path,
resulting in jitter, instability, or degraded performance.
High-power traces, bolded in the typical application cir-
cuits (Figure 1 and Figure 2), should be as short and wide
as possible. Additionally, the current loops formed by the
tor’s voltage rating exceeds V
and that the induc-
IN(MAX)
tor value exceeds the minimum inductance recommended
in the Inductor Selection section.
Inverter Configuration
Figure 7 shows the MAX1836/MAX1837 in a floating
ground configuration. By connecting what would nor-
mally be the output to the supply-voltage ground, the IC’s
ground pin is forced to regulate to -5V (MAX183_EUT50)
or -3.3V (MAX183_EUT33). Avoid exceeding the maxi-
mum ratings of 24V between IN and GND, and 5.5V
between OUT and GND. Other negative voltages may be
generated by placing a resistive divider across the output
capacitor and connecting the tap to FB in the same man-
ner as the normal step-down configuration.
power components (C , C
, L1, and D1) should be
OUT
IN
as tight as possible to avoid radiated noise. Connect the
ground pins of these power components at a common
node in a star-ground configuration. Separate the noisy
traces, such as the LX node, from the feedback network
with grounded copper. Furthermore, keep the extra cop-
per on the board, and integrate it into a pseudoground
plane. When using external feedback, place the resistors
as close to the feedback pin as possible to minimize noise
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MAX1836/MAX1837
24V Internal Switch, 100% Duty Cycle,
Step-Down Converters
L1
47µH
OUTPUT
5V
INPUT
4.5V TO 24V
L1
47µH
INPUT
3.6V TO 18V
IN
LX
IN
LX
C
OUT
C
IN
C
D1
IN
SHDN
68µF
10V
OUT
10µF
25V
SHDN
10µF
MAX1837
C
OUT
D1
MAX1836
MAX1837
OUT
FB
100µF
OUTPUT
-3.3V OR -5V
GND
FB
GND
NOTE: HIGH-CURRENT PATHS SHOWN WITH BOLD LINES.
C
IN
= TAIYO YUDEN TMK432BJ106KM
L1 = SUMIDA CDRH5D28-470
= SANYO POSCAP 10TPC68M
D1 = NIHON EP05Q03L
C
OUT
Figure 7. MAX1836/MAX1837 Inverter Configuration
NOTE: HIGH-CURRENT PATHS SHOWN WITH BOLD LINES.
Chip Information
TRANSISTOR COUNT: 731
PROCESS: BiCMOS
Figure 6. High-Voltage Application
Selector Guide
PRESET OUTPUT
VOLTAGE (V)
LOAD CURRENT
(mA)
PART
MAX1836ETT33
MAX1836ETT50
MAX1836EUT33
MAX1836EUT50
MAX1837ETT33
MAX1837ETT50
MAX1837EUT33
MAX1837EUT50
3.3
5
125
125
125
125
250
250
250
250
3.3
5
3.3
5
3.3
5
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MAX1836/MAX1837
24V Internal Switch, 100% Duty Cycle,
Step-Down Converters
Package Information
For the latest package outline information and land patterns (footprints), go to www.maximintegrated.com/packages. Note that a “+”,
“#”, or “-” in the package code indicates RoHS status only. Package drawings may show a different suffix character, but the drawing
pertains to the package regardless of RoHS status.
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MAX1836/MAX1837
24V Internal Switch, 100% Duty Cycle,
Step-Down Converters
Package Information (continued)
For the latest package outline information and land patterns (footprints), go to www.maximintegrated.com/packages. Note that a “+”,
“#”, or “-” in the package code indicates RoHS status only. Package drawings may show a different suffix character, but the drawing
pertains to the package regardless of RoHS status.
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MAX1836/MAX1837
24V Internal Switch, 100% Duty Cycle,
Step-Down Converters
Package Information (continued)
For the latest package outline information and land patterns (footprints), go to www.maximintegrated.com/packages. Note that a “+”,
“#”, or “-” in the package code indicates RoHS status only. Package drawings may show a different suffix character, but the drawing
pertains to the package regardless of RoHS status.
Revision History
Pages changed at Rev 3: 1, 7, 8, 12
For pricing, delivery, and ordering information, please contact Maxim Direct at 1-888-629-4642, or visit Maxim Integrated’s website at www.maximintegrated.com.
Maxim Integrated cannot assume responsibility for use of any circuitry other than circuitry entirely embodied in a Maxim Integrated product. No circuit patent licenses
are implied. Maxim Integrated reserves the right to change the circuitry and specifications without notice at any time. The parametric values (min and max limits)
shown in the Electrical Characteristics table are guaranteed. Other parametric values quoted in this data sheet are provided for guidance.
©
Maxim Integrated and the Maxim Integrated logo are trademarks of Maxim Integrated Products, Inc.
2006 Maxim Integrated Products, Inc.
│ 15
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