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PDF LTM8021 Data sheet ( Hoja de datos )
| Número de pieza | LTM8021 | |
| Descripción | 500mA Step-Down DC/DC Module | |
| Fabricantes | Linear Technology | |
| Logotipo |  |
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Hay una vista previa y un enlace de descarga de LTM8021 (archivo pdf) en la parte inferior de esta página. Total 16 Páginas | ||
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LTM8021
36VIN, 500mA
Step-Down DC/DC µModule
FEATURESwww.datasheet4u.com
n Complete Switch Mode Power Supply
n Wide Input Voltage Range: 3V to 36V
n 500mA Output Current
n 0.8V to 5V Output Voltage
n Fixed 1.1MHz Switching Frequency
n Current Mode Control
n (e4) RoHS Compliant Package with Gold
Pad Finish
n Programmable Soft-Start
n Tiny, Low Profile (11.25mm × 6.25mm × 2.82mm)
Surface Mount LGA Package
APPLICATIONS
n Automotive Battery Regulation
n Power for Portable Products
n Distributed Supply Regulation
n Industrial Supplies
n Wall Transformer Regulation
DESCRIPTION
The LTM®8021 is a 36VIN 500mA, step-down DC/DC
μModuleTM. Included in the package are the switching
controller, power switches, inductor, and all support
components. Operating over an input voltage range of 3V
to 36V, the LTM8021 supports an output voltage range of
0.8V to 5V, set by a single resistor. Only an output and
bulk input capacitor are needed to finish the design.
The low profile package (2.82mm) enables utilization of
unused space on the bottom of PC boards for high den-
sity point of load regulation. A built-in soft-start timer is
adjustable with just a resistor and capacitor.
The LTM8021 is packaged in a thermally enhanced,
compact (11.25mm × 6.25mm) and low profile (2.82mm)
overmolded Land Grid Array (LGA) package suitable
for automated assembly by standard surface mount
equipment. The LTM8021 is RoHS compliant.
, LT, LTC and LTM are registered trademarks of Linear Technology Corporation.
μModule is a trademark of Linear Technology Corporation. All other trademarks are the
property of their respective owners.
TYPICAL APPLICATION
7VIN to 36VIN, 5V/500mA μModule Regulator
VIN*
7V TO
36V
LTM8021
IN OUT
RUN/SS
GND
1μF
BIAS
ADJ
19.1k
VOUT
5V AT 500mA
2.2μF
8021 TA01a
*RUNNING VOLTAGE RANGE. PLEASE REFER TO THE
APPLICATIONS INFORMATION SECTION FOR START-UP DETAILS.
Efficiency and Power Loss
90 450
80
EFFICIENCY
70
400
350
300
250
60
200
50 150
POWER
40
LOSS
100
50
30
1.00
10.00
100.00
LOAD CURRENT (mA)
0
1000.00
8021 TA01b
8021fb
1
1 page  
LTM8021
TYPICAL PERFORMANCE CHARACTERISTICS TA = 25°C, unless otherwise noted
Input Current vs Output Current
www.data40s0heet4u.com
VIN = 5V
350
VOUT = 3.3V
300
250
200 VOUT = 2.5V
150 VOUT = 1.8V
100
50
0
0 50 100 150 200 250 300 350 400 450 500
OUTPUT CURRENT (mA)
8021 G09
Input Quiescent Current
vs Input Voltage
3000
VO = 3.3V
2500
2000
1500
1000
500
0
0 5 10 15 20 25 30 35 40
INPUT VOLTAGE (V)
8021 G12
Input Current vs Output Current
300
VIN = 12V
250
VOUT = 5V
200 VOUT = 3.3V
150 VOUT = 2.5V
100
50 VOUT = 1.8V
0
0 50 100 150 200 250 300 350 400 450 500
OUTPUT CURRENT (mA)
8021 G10
Minimum Input Running Voltage
vs Output Voltage
7
IOUT = 500mA
6
5
4
3
2
1
0
0123 4 56
OUTPUT VOLTAGE (V)
8021 G13
Input Current vs Output Current
140
VIN = 24V
120 VOUT = 5V
100 VOUT = 3.3V
80
VOUT = 2.5V
60
40
VOUT = 1.8V
20
0
0 50 100 150 200 250 300 350 400 450 500
OUTPUT CURRENT (mA)
8021 G11
Output Short-Circuit Current
vs Input Voltage
900
VOUT = 3.3V
880
860
840
820
800
780
760
740
720
4
8 12 16 20 24 28 32 36
INPUT VOLTAGE (V)
8021 G14
8021fb
5
5 Page 
LTM8021
APPLICATIONS INFORMATION
PCB Layout
Most of the problems associated with the PCB layout
wwwh.daavtaeshbeeeet4nu.caolmleviated or eliminated by the high level of
integration of the LTM8021. The LTM8021 is nevertheless
a switching power supply, and care must be taken to
minimize EMI and ensure proper operation. Even with the
high level of integration, one may fail to achieve a specified
operation with a haphazard or poor layout. See Figure 4
for a suggested layout.
Ensure that the grounding and heatsinking are acceptable.
A few rules to keep in mind are:
1. Place the CIN capacitor as close as possible to the VIN
and GND connection of the LTM8021.
2. Place the COUT capacitor as close as possible to the
VOUT and GND connection of the LTM8021.
3. Place the CIN and COUT capacitors such that their ground
currents flow directly adjacent to, or underneath, the
LTM8021.
4. Connect all of the GND connections to as large a
copper pour or plane area as possible on the top layer.
Avoid breaking the ground connection between the
external components and the LTM8021.
VIN GND PLANE VOUT
CIN COUT
RADJ
RUN/SS
FB
Hot-Plugging Safely
The small size, robustness and low impedance of ceramic
capacitors make them an attractive option for the input
bypass capacitor of LTM8021. However, these capacitors
can cause problems if the LTM8021 is plugged into a live
supply (see the Linear Technology Application Note 88 for
a complete discussion). The low loss ceramic capacitor
combined with stray inductance in series with the power
source forms an under damped tank circuit, and the volt-
age at the VIN pin of the LTM8021 can ring to twice the
nominal input voltage, possibly exceeding the LTM8021’s
rating and damaging the part. If the input supply is poorly
controlled or the user will be plugging the LTM8021 into
an energized supply, the input network should be designed
to prevent this overshoot. Figure 5 shows the waveforms
that result when an LTM8021 circuit is connected to a 24V
supply through six feet of 24-gauge twisted pair. The first
plot is the response with a 2.2μF ceramic capacitor at the
input. The input voltage rings as high as 35V and the input
current peaks at 20A. One method of damping the tank
circuit is to add another capacitor with a series resistor to
the circuit. In Figure 5b an aluminum electrolytic capacitor
has been added. This capacitor’s high equivalent series
resistance damps the circuit and eliminates the voltage
overshoot. The extra capacitor improves low frequency
ripple filtering and can slightly improve the efficiency of
the circuit, though it is likely to be the largest component
in the circuit. An alternative solution is shown in Figure
5c. A 0.7Ω resistor is added in series with the input to
eliminate the voltage overshoot (it also reduces the peak
input current). A 0.1μF capacitor improves high frequency
filtering. This solution is smaller and less expensive than
the electrolytic capacitor. For high input voltages its impact
on efficiency is minor, reducing efficiency less than one half
percent for a 5V output at full load operating from 24V.
8021 F04
Figure 4. Layout Showing Suggested External Components,
GND Plane and Thermal Vias
8021fb
11
11 Page | ||
| Páginas | Total 16 Páginas | |
| PDF Descargar | [ Datasheet LTM8021.PDF ] | |
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