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PDF LM3100 Data sheet ( Hoja de datos )
| Número de pieza | LM3100 | |
| Descripción | Voltage Regulator | |
| Fabricantes | National Semiconductor | |
| Logotipo |  |
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February 2006
LM3100
SIMPLE SWITCHER® Synchronous 1MHz 1.5A
Step-Down Voltage Regulator
General Description
The LM3100 Synchronously Rectified Buck Converter fea-
tures all functions needed to implement a highly efficient,
cost effective buck regulator capable of supplying 1.5A to
loads with voltages as low as 0.8V. Dual 40V N-Channel
synchronous MOSFET switches allow for low external com-
ponent thus reducing complexity and minimizing board
space. The LM3100 is designed to work exceptionally well
with ceramic and other very low ESR output capacitors. The
Constant ON-Time (COT) regulation scheme requires no
loop compensation, results in fast load transient response,
and simplifies circuit implementation. Through the use of a
unique design the regulator does not rely on output capacitor
ESR for stability, as do most other COT regulators. The
operating frequency remains nearly constant with line and
load variations due to the inverse relationship between the
input voltage and the on-time. The oprating frequency can
be externally programmed up to 1MHz. Protection features
include VCC under-voltage lockout, thermal shutdown and
gate drive under-voltage lockout. The part is available in a
thermally enhanced eTSSOP-20 package
Features
n Input voltage range 4.5V - 36V
n 1.5A output current
n 0.8V, ±1.5% reference
n Integrated 40V, dual N-Channel buck synchronous
switches
n Low component count and small solution size
n No loop compensation required
n Ultra-fast transient response
n Stable with ceramic and other low ESR capacitors
n Programmable switching frequency up to 1MHz
n Max. duty cycle limited during start-up
n Valley current limit
n Precision Internal Reference for adjustable output
voltage down to 0.8V
n Thermal shutdown
n Thermally enhanced eTSSOP-20 package
Typical Applications
n 5VDC, 12VDC, 24VDC, 12VAC, and 24VAC systems
n Embedded Systems
n Industrial Controls
n Automotive Telematics and Body Electronics
n Point of Load Regulators
n Storage Systems
n Broadband Infrastructure
n Direct Conversion from 2/3/4 Cell Lithium Batteries
Systems
Typical Application
SIMPLE SWITCHER® is a registered trademark of National Semiconductor Corporation
© 2006 National Semiconductor Corporation DS201747
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20174702
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1 page  
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Electrical Charateristics Specifications with standard type are for TJ = 25˚C only; limits in boldface type apply
over the full Operating Junction Temperature (TJ) range. 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. Unless otherwise stated the following conditions apply: VIN = 18V, VOUT = 3.3V. (Continued)
Symbol
TSD-HYS
Parameter
Thermal shutdown temperature
hysteresis
Conditions
TJ falling
Min Typ Max Units
20 ˚C
Note 1: Absolute Maximum Ratings are limits beyond which damage to the device may occur. Operating Ratings are conditions under which operation of the device
is intended to be functional. For guaranteed specifications and test conditions, see the Electrical Characteristics.
Note 2: The human body model is a 100pF capacitor discharged through a 1.5kΩ resistor into each pin.
Note 3: θJC measurements are performed in general accordance with Mil-Std 883B, Method 1012.1 and utilizes the copper heat sink technique. Copper Heat Sink
@ 60˚C.
Note 4: VCC provides self bias for the internal gate drive and control circuits. Device thermal limitations limit external loading.
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ON-Time Timer, Shutdown (Continued)
(5)
The LM3100 can be remotely shut down by taking the EN pin
below 1.1V. Refer to Figure 1. In this mode the SS pin is
internally grounded, the on-timer is disabled, and bias cur-
rents are reduced. Releasing the EN pin allows normal
operation to resume. The voltage at the EN pin is between
1.5V and 3.0V, depending on VIN and the pull-up resistor.
20174704
FIGURE 1. Shutdown Implementation
Current Limit
Current limit detection occurs during the off-time by monitor-
ing the re-circulating current through the low-side synchro-
nous switch. Referring to Functional Block Diagram, when
the buck switch is turned off, inductor current flows through
the load, into PGND, and through the internal low-side syn-
chronous switch. If that current exceeds 1.9A the current
limit comparator toggles, forcing a delay to the start of the
next on-time period. The next cycle starts when the re-
circulating current falls back below 1.9A and the voltage at
FB is below 0.8V. The inductor current is monitored during
the low-side switch on-time. As long as the overload condi-
tion persists and the inductor current exceeds 1.9A, the
high-side switch will remain inhibited. The operating fre-
quency is lower during an over-current due to longer than
normal off-times.
Figure 2 illustrates the inductor current waveform. During
normal operation the load current is low, the average of the
ripple waveform. When an overload occurs the current ratch-
ets up until it exceeds 1.9A. During the Current Limited
portion of Figure 2, the current ramps down to 1.9A during
each off-time, initiating the next on-time (assuming the volt-
age at FB is <0.8V). During each on-time the current ramps
up an amount equal to:
(6)
During this time the LM3100 is in a constant current mode,
with an average load current (IOCL) equal to 1.9A +∆I/2.
FIGURE 2. Inductor Current - Current Limit Operation
20174705
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| PDF Descargar | [ Datasheet LM3100.PDF ] | |
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