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National Semiconductor
National Semiconductor

LM20123 Datasheet

Synchronous Buck Regulator


LM20123 Datasheet Preview


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 mintegrated 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
Page 1

www.DataShCeeot4Un.cnomection Diagram
Ordering Information
Order Number
LM20123MH
LM20123MHE
LM20123MHX
Package Type
eTSSOP-16
30030102
Top View
eTSSOP-16 Package
NSC Package Drawing
MXA16A
Package Marking
20123MH
Supplied As
92 Units of Rail
250 Units of Tape and Reel
2500 Units of Tape and Reel
Pin Descriptions
Pin #
1
2
3
4
5,16
6,7
8,9
10,11
12
13
14
15
EP
Name
SS/TRK
FB
PGOOD
COMP
NC
PVIN
SW
PGND
EN
VCC
AVIN
AGND
Exposed Pad
Description
Soft-Start or Tracking control input. An internal 5 µA current source charges an external capacitor to
set the Soft-Start ramp rate. If driven by a external source less than 800 mV, this pin overrides the
internal reference that sets the output voltage. If left open, an internal 1ms Soft-Start ramp is activated.
Feedback input to the error amplifier from the regulated output. This pin is connected to the inverting
input of the internal transconductance error amplifier. An 800 mV reference connected to the non-
inverting input of the error amplifier sets the closed loop regulation voltage at the FB pin.
Power good output signal. Open drain output indicating the output voltage is regulating within tolerance.
A pull-up resistor of 10 kto 100 kis recommend for most applications.
External compensation pin. Connect a resistor and capacitor to this pin to compensate the device.
These pins must be connected to GND to ensure proper operation.
Input voltage to the power switches inside the device. These pins should be connected together at the
device. A low ESR capacitor should be placed near these pins to stabilize the input voltage.
Switch pin. The PWM output of the internal power switches.
Power ground pin for the internal power switches.
Precision enable input for the device. An external voltage divider can be used to set the device turn-
on threshold. If not used the EN pin should be connected to PVIN.
Internal 2.7V sub-regulator. This pin should be bypassed with a 1 µF ceramic capacitor.
Analog input supply that generates the internal bias. Must be connected to VIN through a low pass RC
filter.
Quiet analog ground for the internal bias circuitry.
Exposed metal pad on the underside of the package with a weak electrical connection to ground. It is
recommended to connect this pad to the PC board ground plane in order to improve heat dissipation.
www.national.com
2
Page 2

wwAwb.DsatoaSlhueette4UM.coamximum Ratings (Note 1)
If Military/Aerospace specified devices are required,
please contact the National Semiconductor Sales Office/
Distributors for availability and specifications.
Voltages from the indicated pins to GND
AVIN, PVIN, EN, PGOOD, SS/
TRK, COMP, FB, SW
Storage Temperature
Junction Temperature
-0.3V to +6V
-65°C to 150°C
150°C
Power Dissipation (Note 2)
Lead Temperature (Soldering,
10 sec)
Minimum ESD Rating (Note
3)
Operating Ratings
PVIN, AVIN to GND
Junction Temperature
2.6W
260°C
±2kV
2.95V to 5.5V
−40°C to + 125°C
Electrical Characteristics Unless otherwise stated, the following conditions apply: AVIN = PVIN = VIN = 5V.
Limits in standard type are for TJ = 25°C only, limits in bold face 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.
Symbol
Parameter
Conditions
Min Typ Max Unit
VFB
ΔVOUTIOUT
ICL
RDS_ON
Feedback pin voltage
Load Regulation
Switch Current Limit Threshold
High-Side Switch On Resistance
VIN = 2.95V to 5.5V
IOUT = 100 mA to 3A
VIN = 3.3V
ISW = 3.5A
0.788 0.8 0.812
0.08
4.3 4.8 5.3
36 55
V
%/A
A
m
RDS_ON
Low-Side Switch On Resistance
ISW = 3.5A
32 52 m
IQ
ISD
VUVLO
VUVLO_HYS
VVCC
ISS
VTRACK
Oscillator
Operating Quiescent Current
Shutdown Quiescent current
VIN Under Voltage Lockout
VIN Under Voltage Lockout Hysteresis
VCC Voltage
Soft-Start Pin Source Current
SS/TRK Accuracy, VSS - VFB
Non-switching, VFB = VCOMP
VEN = 0V
Rising VIN
Falling VIN
IVCC = 0 µA
VSS/TRK = 0V
VSS/TRK = 0.4V
2.45
2.45
2
-10
3.5 6
90 180
2.7 2.95
45 100
2.7 2.95
4.5 7
3 15
mA
µA
V
mV
V
µA
mV
FOSC
Oscillator Frequency
DCMAX
Maximum Duty Cycle
TON_TIME
Minimum On Time
TCL_BLANK
Current Sense Blanking Time
Error Amplifier and Modulator
ILOAD = 0A
After Rising VSW
1350
1500
85
100
80
1650
kHz
%
ns
ns
IFB
ICOMP_SRC
ICOMP_SNK
gm
AVOL
Power Good
Feedback pin bias current
COMP Output Source Current
COMP Output Sink Current
Error Amplifier Transconductance
Error Amplifier Voltage Gain
VFB = 0.8V
VFB = VCOMP = 0.6V
VFB = 1.0V, VCOMP = 0.6V
ICOMP = ± 50 µA
1 100 nA
80 100
µA
80 100
µA
450 510 600 µmho
2000
V/V
VOVP
VOVP_HYS
VPGTH
VPGHYS
TPGOOD
IOL
IOH
Over Voltage Protection Rising Threshold
Over Voltage Protection Hysteresis
PGOOD Rising Threshold
PGOOD Falling Hysteresis
PGOOD deglitch time
PGOOD Low Sink Current
PGOOD High Leakage Current
With respect to VFB
With respect to VFB
VPGOOD = 0.4V
VPGOOD = 5V
105 108 111
23
92 94 96
23
16
0.6 1
5 100
%
%
%
%
µs
mA
nA
3 www.national.com
Page 3
Part Number LM20123
Manufactur National Semiconductor
Description Synchronous Buck Regulator
Total Page 20 Pages
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