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PDF LM2830 Data sheet ( Hoja de datos )
| Número de pieza | LM2830 | |
| Descripción | High Frequency 1.0A Load - Step-Down DC-DC Regulator | |
| Fabricantes | National Semiconductor | |
| Logotipo |  |
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Hay una vista previa y un enlace de descarga de LM2830 (archivo pdf) en la parte inferior de esta página. Total 24 Páginas | ||
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www.DataSheet4U.com
August 2006
LM2830
High Frequency 1.0A Load - Step-Down DC-DC
Regulator
General Description
The LM2830 regulator is a monolithic, high frequency, PWM
step-down DC/DC converter in a 5 pin SOT23 and a 6 Pin
LLP package. It provides all the active functions to provide
local DC/DC conversion with fast transient response and
accurate regulation in the smallest possible PCB area. With
a minimum of external components, the LM2830 is easy to
use. The ability to drive 1.0A loads with an internal 130 mΩ
PMOS switch using state-of-the-art 0.5 µm BiCMOS technol-
ogy results in the best power density available. The world-
class control circuitry allows on-times as low as 30ns, thus
supporting exceptionally high frequency conversion over the
entire 3V to 5.5V input operating range down to the minimum
output voltage of 0.6V. Switching frequency is internally set
to 1.6 MHz, or 3.0 MHz, allowing the use of extremely small
surface mount inductors and chip capacitors. Even though
the operating frequency is high, efficiencies up to 93% are
easy to achieve. External shutdown is included, featuring an
ultra-low stand-by current of 30 nA. The LM2830 utilizes
current-mode control and internal compensation to provide
high-performance regulation over a wide range of operating
conditions. Additional features include internal soft-start cir-
cuitry to reduce inrush current, pulse-by-pulse current limit,
thermal shutdown, and output over-voltage protection.
Features
n Space Saving SOT23-5 Package
n Input voltage range of 3.0V to 5.5V
n Output voltage range of 0.6V to 4.5V
n 1.0A output current
n High Switching Frequencies
1.6MHz (LM2830X)
3.0MHz (LM2830Z)
n 130mΩ PMOS switch
n 0.6V, 2% Internal Voltage Reference
n Internal soft-start
n Current mode, PWM operation
n Thermal Shutdown
n Over voltage protection
Applications
n Local 5V to Vcore Step-Down Converters
n Core Power in HDDs
n Set-Top Boxes
n USB Powered Devices
n DSL Modems
Typical Application Circuit
20197464
20197481
© 2006 National Semiconductor Corporation DS201974
www.national.com
1 page  
Electrical Characteristics VIN = 5V unless otherwise indicated under the Conditions column. Limits in
standard type are for TJ = 25˚C only; limits in boldface type apply over the junction temperature (TJ) range of -40˚C to
+125˚C. Minimum and Maximum limits are guaranteed through test, design, or statistical correlation. Typical values represent
the most likely parametric norm at TJ = 25˚C, and are provided for reference purposes only. (Continued)
Symbol
θJA
θJC
TSD
Parameter
Junction to Ambient
0 LFPM Air Flow (Note 3)
Junction to Case (Note 3)
Thermal Shutdown Temperature
Conditions
LLP-6 Package
SOT23-5 Package
LLP-6 Package
SOT23-5 Package
Min Typ Max Units
80
˚C/W
118
18
˚C/W
80
165 ˚C
Note 1: Absolute maximum ratings indicate limits beyond which damage to the device may occur. Operating Range indicates conditions for which the device is
intended to be functional, but does not guarantee specfic performance limits. For guaranteed specifications and test conditions, see the Electrical Characteristics.
Note 2: Thermal shutdown will occur if the junction temperature exceeds the maximum junction temperature of the device.
Note 3: Applies for packages soldered directly onto a 3” x 3” PC board with 2oz. copper on 4 layers in still air.
5 www.national.com
5 Page 
Design Guide (Continued)
FIGURE 3. Inductor Current
20197405
INPUT CAPACITOR
An input capacitor is necessary to ensure that VIN does not
drop excessively during switching transients. The primary
specifications of the input capacitor are capacitance, volt-
age, RMS current rating, and ESL (Equivalent Series Induc-
tance). The recommended input capacitance is 22 µF.The
input voltage rating is specifically stated by the capacitor
manufacturer. Make sure to check any recommended derat-
ings and also verify if there is any significant change in
capacitance at the operating input voltage and the operating
temperature. The input capacitor maximum RMS input cur-
rent rating (IRMS-IN) must be greater than:
Neglecting inductor ripple simplifies the above equation to:
In general,
∆iL = 0.1 x (IOUT) → 0.2 x (IOUT)
If ∆iL = 20% of 1A, the peak current in the inductor will be
1.2A. The minimum guaranteed current limit over all operat-
ing conditions is 1.2A. One can either reduce ∆iL, or make
the engineering judgment that zero margin will be safe
enough. The typical current limit is 1.75A.
The LM2830 operates at frequencies allowing the use of
ceramic output capacitors without compromising transient
response. Ceramic capacitors allow higher inductor ripple
without significantly increasing output ripple. See the output
capacitor section for more details on calculating output volt-
age ripple. Now that the ripple current is determined, the
inductance is calculated by:
Where
When selecting an inductor, make sure that it is capable of
supporting the peak output current without saturating. Induc-
tor saturation will result in a sudden reduction in inductance
and prevent the regulator from operating correctly. Because
of the speed of the internal current limit, the peak current of
the inductor need only be specified for the required maxi-
mum output current. For example, if the designed maximum
output current is 1.0A and the peak current is 1.25A, then the
inductor should be specified with a saturation current limit of
> 1.25A. There is no need to specify the saturation or peak
current of the inductor at the 1.75A typical switch current
limit. The difference in inductor size is a factor of 5. Because
of the operating frequency of the LM2830, ferrite based
inductors are preferred to minimize core losses. This pre-
sents little restriction since the variety of ferrite-based induc-
tors is huge. Lastly, inductors with lower series resistance
(RDCR) will provide better operating efficiency. For recom-
mended inductors see Example Circuits.
It can be shown from the above equation that maximum
RMS capacitor current occurs when D = 0.5. Always calcu-
late the RMS at the point where the duty cycle D is closest to
0.5. The ESL of an input capacitor is usually determined by
the effective cross sectional area of the current path. A large
leaded capacitor will have high ESL and a 0805 ceramic chip
capacitor will have very low ESL. At the operating frequen-
cies of the LM2830, leaded capacitors may have an ESL so
large that the resulting impedance (2πfL) will be higher than
that required to provide stable operation. As a result, surface
mount capacitors are strongly recommended.
Sanyo POSCAP, Tantalum or Niobium, Panasonic SP, and
multilayer ceramic capacitors (MLCC) are all good choices
for both input and output capacitors and have very low ESL.
For MLCCs it is recommended to use X7R or X5R type
capacitors due to their tolerance and temperature character-
istics. Consult capacitor manufacturer datasheets to see
how rated capacitance varies over operating conditions.
OUTPUT CAPACITOR
The output capacitor is selected based upon the desired
output ripple and transient response. The initial current of a
load transient is provided mainly by the output capacitor. The
output ripple of the converter is:
When using MLCCs, the ESR is typically so low that the
capacitive ripple may dominate. When this occurs, the out-
put ripple will be approximately sinusoidal and 90˚ phase
shifted from the switching action. Given the availability and
quality of MLCCs and the expected output voltage of designs
using the LM2830, there is really no need to review any other
capacitor technologies. Another benefit of ceramic capaci-
tors is their ability to bypass high frequency noise. A certain
amount of switching edge noise will couple through parasitic
capacitances in the inductor to the output. A ceramic capaci-
tor will bypass this noise while a tantalum will not. Since the
output capacitor is one of the two external components that
control the stability of the regulator control loop, most appli-
cations will require a minimum of 22 µF of output capaci-
tance. Capacitance often, but not always, can be increased
11 www.national.com
11 Page | ||
| Páginas | Total 24 Páginas | |
| PDF Descargar | [ Datasheet LM2830.PDF ] | |
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