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PDF MAX1837 Data sheet ( Hoja de datos )
| Número de pieza | MAX1837 | |
| Descripción | Step-Down Converters | |
| Fabricantes | Maxim Integrated | |
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Hay una vista previa y un enlace de descarga de MAX1837 (archivo pdf) en la parte inferior de esta página. Total 15 Páginas | ||
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MAX1836/MAX1837
EVALUATION KIT AVAILABLE
24V Internal Switch, 100% Duty Cycle,
Step-Down Converters
General Description
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
to VIN. 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 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.
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.
Applications
●● 9V Battery Systems
●● Notebook Computers
●● Distributed Power Systems
●● Backup Supplies
●● 4mA to 20mA Loop Power Supplies
●● Industrial Control Supplies
●● Handheld Devices
Typical Operating Circuit
INPUT
4.5V TO 24V
IN LX
SHDN
MAX1836
MAX1837 OUT
OUTPUT
3.3V OR 5V
GND FB
NOTE: HIGH-CURRENT PATHS SHOWN WITH BOLD LINES.
Features
●● 4.5V to 24V Input Voltage Range
●● Preset 3.3V or 5V Output
●● Adjustable Output from 1.25V to VIN
●● 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
TEMP RANGE
PIN-
PACKAGE
MAX1836ETT33-T
MAX1836ETT50-T
MAX1836EUT33-T
MAX1836EUT50-T
MAX1837ETT33-T
MAX1837ETT50-T
MAX1837EUT33-T
MAX1837EUT50-T
*EP = Exposed pad.
T = Tape and reel.
-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
6 TDFN-EP*
6 TDFN-EP*
6 SOT23
6 SOT23
6 TDFN-EP*
6 TDFN-EP*
6 SOT23
6 SOT23
Selector Guide appears at end of data sheet.
TOP
MARK
AJG
AJE
AANY
AANW
AJH
AJF
AANZ
AANX
Pin Configurations
TOP VIEW
FB 1
GND 2
IN 3
6 OUT
FB 1
MAX1836
GND 2
MAX1837 5 SHDN
IN 3
4 LX
MAX1836
MAX1837
TDFN
6 OUT
5 SHDN
4 LX
SOT23
19-1919; Rev 3; 7/06
1 page  
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.)
MAX1837EUT33
EFFICIENCY vs. INPUT VOLTAGE
100
FIGURE 2
95
VOUT = 3.3V
L1 = 47µH
90
85 IOUT = 200mA
80
MAX1837EUT33
SWITCHING FREQUENCY vs. INPUT VOLTAGE
100
IOUT = 200mA
MAX1837EUT33
PEAK INDUCTOR CURRENT vs. INPUT VOLTAGE
1000
FIGURE 2
VOUT = 3.3V
800 L1 = 47µH
IOUT = 200mA
IOUT = 10mA
FIGURE 2
600
10 VOUT = 3.3V
L1 = 47µH
400
75
70
0
IOUT = 10mA
4 8 12 16 20
INPUT VOLTAGE (V)
24
1
0
MAX1837EUT50
OUTPUT VOLTAGE vs. LOAD CURRENT
5.04
VIN = 12V TO 24V
VIN = 9V
5.02
5.00
IOUT = 10mA
4 8 12 16 20
INPUT VOLTAGE (V)
24
200
LIMITED BY
tON(MIN)
0
04
8
LIMITED BY
ILIM
12 16
INPUT VOLTAGE (V)
20
24
MAX1837EUT50
EFFICIENCY vs. LOAD CURRENT
100
FIGURE 6
95 VOUT = 5V
VIN = 7V
VIN = 9V
90 VIN = 12V
85
4.98 VIN = 7V
FIGURE 6
4.96
0 50 100 150 200
LOAD CURRENT (mA)
250
300
MAX1837EUT50
DROPOUT VOLTAGE vs. LOAD CURRENT
400
FIGURE 6
350 VOUT = 5V
300
250
200
150
100
50
0
0
100 200
LOAD CURRENT (mA)
300
80
75
VIN = 24V
VIN = 18V
70
0.1
15
1 10 100
LOAD CURRENT (mA)
1000
NO-LOAD SUPPLY CURRENT
vs. INPUT VOLTAGE
14
13
12
11
10
0
4 8 12 16 20
INPUT VOLTAGE (V)
24
www.maximintegrated.com
Maxim Integrated │ 5
5 Page 
MAX1836/MAX1837
24V Internal Switch, 100% Duty Cycle,
Step-Down Converters
Table 1. Component Suppliers
SUPPLIER
INDUCTORS
Coilcraft
Coiltronics
Sumida USA
Toko
CAPACITORS
AVX
Kemet
Panasonic
Sanyo
Taiyo Yuden
DIODES
Central Semiconductor
International Rectifier
Nihon
On Semiconductor
Zetex
PHONE
847-639-6400
561-241-7876
847-956-0666
847-297-0070
803-946-0690
408-986-0424
847-468-5624
619-661-6835
408-573-4150
516-435-1110
310-322-3331
847-843-7500
602-303-5454
516-543-7100
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.
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
power components (CIN, COUT, L1, and D1) should be
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
FAX
WEBSITE
847-639-1469
561-241-9339
847-956-0702
847-699-1194
www.coilcraft.com
www.coiltronics.com
www.sumida.com
www.tokoam.com
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
www.t-yuden.com
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
www.onsemi.com
www.zetex.com
coupling. The MAX1837 evaluation kit shows the recom-
mended layout.
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-
tor’s voltage rating exceeds VIN(MAX) and that the induc-
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.
www.maximintegrated.com
Maxim Integrated │ 11
11 Page | ||
| Páginas | Total 15 Páginas | |
| PDF Descargar | [ Datasheet MAX1837.PDF ] | |
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