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PDF LM20123 Data sheet ( Hoja de datos )
| Número de pieza | LM20123 | |
| Descripción | Synchronous Buck Regulator | |
| Fabricantes | National Semiconductor | |
| Logotipo |  |
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Hay una vista previa y un enlace de descarga de LM20123 (archivo pdf) en la parte inferior de esta página. Total 20 Páginas | ||
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www.DataSheet4U.com
January 16, 2008
LM20123
3A, 1.5MHz PowerWise® Synchronous Buck Regulator
General Description
The LM20123 is a full featured 1.5 MHz synchronous buck
regulator capable of delivering up to 3A of continuous output
current. The current mode control loop can be compensated
to be stable with virtually any type of output capacitor. For
most cases, compensating the device only requires two ex-
ternal components, providing maximum flexibility and ease of
use. The device is optimized to work over the input voltage
range of 2.95V to 5.5V making it suited for a wide variety of
low voltage systems.
The device features internal over voltage protection (OVP)
and over current protection (OCP) circuits for increased sys-
tem reliability. A precision enable pin and integrated UVLO
allows the turn on of the device to be tightly controlled and
sequenced. Start-up inrush currents are limited by both an
internally fixed and externally adjustable Soft-Start circuit.
Fault detection and supply sequencing is possible with the
integrated power good circuit.
The LM20123 is designed to work well in multi-rail power
supply architectures. The output voltage of the device can be
configured to track a higher voltage rail using the SS/TRK pin.
If the output of the LM20123 is pre-biased at startup it will not
sink current to pull the output low until the internal soft-start
ramp exceeds the voltage at the feedback pin.
The LM20123 is offered in a 16-pin eTSSOP package with an
exposed pad that can be soldered to the PCB, eliminating the
need for bulky heatsinks.
Features
■ Input voltage range 2.95V to 5.5V
■ Accurate current limit minimizes inductor size
■ 96% efficiency with 1.5 MHz switching frequency
■ 32 mΩ integrated FET switches
■ Starts up into pre-biased loads
■ Output voltage tracking
■ Peak current mode control
■ Adjustable output voltage down to 0.8V
■ Adjustable Soft-Start with external capacitor
■ Precision enable pin with hysteresis
■ Integrated OVP, UVLO, power good and thermal
shutdown
■ eTSSOP-16 exposed pad package
Applications
■ Simple to design, high efficiency point of load regulation
from a 5V or 3.3V bus
■ High Performance DSPs, FPGAs, ASICs and
microprocessors
■ Broadband, Networking and Optical Communications
Infrastructure
Typical Application Circuit
PowerWise® is a registered trademark of National Semiconductor Corporation.
© 2008 National Semiconductor Corporation 300301
30030101
www.national.com
1 page  
www.DataSheetE4rUr.ocromAmplifier Gain vs. Frequency
Line Regulation
Load Regulation
30030136
30030137
Feedback Pin Voltage vs. Temperature
30030138
Switching Frequency vs. Temperature
30030151
Quiescent Current vs. VIN (Not Switching)
30030139
5
30030140
www.national.com
5 Page 
the junction cools to approximately 150°C, the part starts up
wwuwsi.nDgathaeShneoertm4Ual.csotamrt up routine. This feature is provided to
prevent catastrophic failures from accidental device over-
heating.
LIGHT LOAD OPERATION
The LM20123 offers increased efficiency when operating at
light loads. Whenever the load current is reduced to a point
where the peak to peak inductor ripple current is greater than
two times the load current, the part will enter the diode emu-
lation mode preventing significant negative inductor current.
The point at which this occurs is the critical conduction bound-
ary and can be calculated by the following equation:
Several diagrams are shown in Figure 1 illustrating continu-
ous conduction mode (CCM), discontinuous conduction
mode, and the boundary condition.
It can be seen that in diode emulation mode, whenever the
inductor current reaches zero the SW node will become high
impedance. Ringing will occur on this pin as a result of the LC
tank circuit formed by the inductor and the parasitic capaci-
tance at the node. If this ringing is of concern an additional
RC snubber circuit can be added from the switch node to
ground.
At very light loads, usually below 100 mA, several pulses may
be skipped in between switching cycles, effectively reducing
the switching frequency and further improving light-load effi-
ciency.
FIGURE 1. Modes of Operation for LM20123
30030105
11
www.national.com
11 Page | ||
| Páginas | Total 20 Páginas | |
| PDF Descargar | [ Datasheet LM20123.PDF ] | |
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