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 V
CC
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
20174702
SIMPLE SWITCHER
®
is a registered trademark of National Semiconductor Corporation
February 2006
LM3100
SIMPLE
SWITCHER
®
Synchronous
1MHz
1.5A
Step-Down
V
oltage
Regulator
© 2006 National Semiconductor Corporation
DS201747
www.national.com
Connection Diagram
20174703
20-lead Plastic
eTSSOP (MXA20A)
Ordering Information
Order Number
Package Type
NSC Package Drawing
Supplied As
LM3100MH
Exposed Pad
TSSOP-20
MXA0020
73 units per Anti-Static Tube
LM3100MHX
2500 Units on Tape and Reel
LM3100
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2
Pin Descriptions
Pin
Name
Description
Application Information
1,9,10,12,19,20
N/C
No Connection
These pins must be left unconnected.
2, 3
SW
Switching Node
Internally connected to the buck switch source.
Connect to output inductor.
4, 5
VIN
Input supply voltage
Supply pin to the device. Nominal input range is
4.5V to 36V.
6
BST
Connection for bootstrap capacitor
Connect a 0.033µF capacitor from SW pin to this
pin. An internal diode charges the capacitor during
the high-side switch off-time.
7
GND
Analog Ground
Ground for all internal circuitry other than the
synchronous switches.
8
SS
Soft-start
An internal 8µA current source charges an external
capacitor to provide the soft- start function.
11
TST
Test mode enable pin
Force the device into test mode. Must be connected
to ground for normal operation.
13
FB
Feedback
Internally connected to the regulation and
over-voltage comparators. The regulation setting is
0.8V at this pin. Connect to feedback divider.
14
EN
Enable pin
Connect a voltage higher than 1.26V to enable the
regulator.
15
RON
On-time Control
An external resistor from VIN to this pin sets the
high-side switch on-time.
16
VCC
Start-up regulator Output
Nominally regulated to 6V. Connect a capacitor of
not less than 680nF between VCC and GND for
stable operation.
17, 18
PGND
Power Ground
Synchronous rectifier MOSFET source connection.
Tie to power ground plane.
DAP
EP
Exposed Pad
Thermal connection pad, connect to GND.
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3
Absolute Maximum Ratings
(Note 1)
If Military/Aerospace specified devices are required,
please contact the National Semiconductor Sales Office/
Distributors for availability and specifications.
VIN, RON to GND
-0.3V to 40V
SW to GND
-0.3V to 40V
SW to GND (Transient)
-2V (
<
100ns)
VIN to SW
-0.3V to 40V
BST to SW
-0.3V to 7V
All Other Inputs to GND
-0.3V to 7V
ESD Rating (Note 2)
Human Body Model
±
2kV
Storage Temperature Range
-65°C to +150°C
Junction Temperature (T
J
)
150°C
Operating Ratings
(Note 1)
Supply Voltage Range (VIN)
4.5V to 36V
Junction Temperature Range (T
J
)
-40°C to + 125°C
Thermal Resistance (
JC
) (Note 3)
6.5°C/W
Electrical Charateristics
Specifications with standard type are for T
J
= 25°C only; limits in boldface type ap-
ply over the full Operating Junction Temperature (T
J
) range. Minimum and Maximum limits are guaranteed through test, de-
sign, or statistical correlation. Typical values represent the most likely parametric norm at T
J
= 25°C, and are provided for ref-
erence purposes only. Unless otherwise stated the following conditions apply: V
IN
= 18V, V
OUT
= 3.3V.
Symbol
Parameter
Conditions
Min
Typ
Max
Units
Start-Up Regulator, V
CC
V
CC
V
CC
output voltage
C
CC
= 680nF, no load
5.0
6.0
7.2
V
V
IN
- V
CC
V
IN
- V
CC
dropout voltage
I
CC
= 2mA
50
140
mV
I
CC
= 20mA
350
570
I
VCCL
V
CC
current limit (Note 4)
V
CC
= 0V
40
65
mA
V
CC-UVLO
V
CC
under-voltage lockout threshold
(UVLO)
V
IN
increasing
3.6
3.75
3.85
V
V
CC-UVLO-HYS
V
CC
UVLO hysteresis
V
IN
decreasing
130
mV
t
VCC-UVLO-D
V
CC
UVLO filter delay
3
µs
I
IN
I
IN
operating current
No switching, V
FB
= 1V
0.7
1
mA
I
IN-SD
I
IN
operating current, Device shutdown V
EN
= 0V
17
30
µA
Switching Characteristics
R
DS-UP-ON
Main MOSFET Rds(on)
0.18
0.35
R
DS- DN-ON
Syn. MOSFET Rds(on)
0.11
0.2
V
G-UVLO
Gate drive voltage UVLO
V
BST
- V
SW
increasing
3.3
4
V
Soft-start
I
SS
SS pin source current
V
SS
= 0.5V
6
8
9.8
µA
Current Limit
I
CL
Syn. MOSFET current limit threshold
1.9
A
ON/OFF Timer
t
ON
ON timer pulse width
V
IN
= 10V, R
ON
= 100 k
1.38
µs
V
IN
= 30V, R
ON
= 100 k
0.47
t
ON-MIN
ON timer minimum pulse width
200
ns
t
OFF
OFF timer pulse width
260
ns
Enable Input
V
EN
EN Pin input threshold
V
EN
rising
1.236
1.26
1.285
V
V
EN-HYS
Enable threshold hysteresis
V
EN
falling
90
mV
Regulation and Over-Voltage Comparator
V
FB
In-regulation feedback voltage
V
SS
0.8V
T
J
= -40°C to + 125°C
0.784
0.8
0.816
V
V
SS
0.8V
T
J
= 0°C to + 125°C
0.788
0.812
V
FB-OV
Feedback over-voltage threshold
0.894
0.920
0.940
V
I
FB
5
100
nA
Thermal Shutdown
T
SD
Thermal shutdown temperature
T
J
rising
165
°C
LM3100
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4
Electrical Charateristics
Specifications with standard type are for T
J
= 25°C only; limits in boldface type apply
over the full Operating Junction Temperature (T
J
) range. Minimum and Maximum limits are guaranteed through test, design, or
statistical correlation. Typical values represent the most likely parametric norm at T
J
= 25°C, and are provided for reference
purposes only. Unless otherwise stated the following conditions apply: V
IN
= 18V, V
OUT
= 3.3V. (Continued)
Symbol
Parameter
Conditions
Min
Typ
Max
Units
T
SD-HYS
Thermal shutdown temperature
hysteresis
T
J
falling
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 1.5k
resistor into each pin.
Note 3:
JC
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: V
CC
provides self bias for the internal gate drive and control circuits. Device thermal limitations limit external loading.
LM3100
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