LM2651
1.5A High Efficiency Synchronous Switching Regulator
General Description
The LM2651 switching regulator provides high efficiency
power conversion over a 100:1 load range (1.5A to 15mA).
This
feature
makes
the
LM2651
an
ideal
fit
in
battery-powered applications that demand long battery life in
both run and standby modes.
Synchronous rectification is used to achieve up to 97% effi-
ciency. At light loads, the LM2651 enters a low power hyster-
etic or "sleep" mode to keep the efficiency high. In many ap-
plications, the efficiency still exceeds 80% at 15mA load. A
shutdown pin is available to disable the LM2651 and reduce
the supply current to less than 10A.
The LM2651 contains a patented current sensing circuitry for
current mode control. This feature eliminates the external
current sensing resistor required by other current-mode
DC-DC converters.
The LM2651 has a 300 kHz fixed frequency internal oscilla-
tor. The high oscillator frequency allows the use of extremely
small, low profile components.
A programmable soft-start feature limits current surges from
the input power supply at start up and provides a simple
means of sequencing multiple power supplies.
Other protection features include input undervoltage lockout,
current limiting, and thermal shutdown.
Features
n
Ultra high efficiency up to 97%
n
High efficiency over a 1.5A to milliamperes load range
n
4V to 14V input voltage range
n
1.8V, 2.5V, 3.3V, or ADJ output voltage
n
Internal MOSFET switch with low R
DS(on)
of 75m
n
300kHz fixed frequency internal oscillator
n
7A shutdown current
n
Patented current sensing for current mode control
n
Input undervoltage lockout
n
Adjustable soft-start
n
Current limit and thermal shutdown
n
16-pin TSSOP package
Applications
n
Personal digital assistants (PDAs)
n
Computer peripherals
n
Battery-powered devices
n
Handheld scanners
n
High efficiency 5V conversion
Typical Application
DS100925-15
Efficiency vs Load Current
(V
IN
= 5V, V
OUT
= 3.3V)
DS100925-1
February 2000
LM2651
1.5A
High
Efficiency
Synchronous
Switching
Regulator
2000 National Semiconductor Corporation
DS100925
www.national.com
Connection Diagram
Ordering Information
V
OUT
Part Number
Package Type
NSC Package
Drawing
Supplied as 94 Units, Rail
Supplied as 2.5k Units, Tape
and Reel
1.8
LM2651MTC-1.8
LM2651MTCX-1.8
TSSOP-16
MTC16
2.5
LM2651MTC-2.5
LM2651MTCX-2.5
3.3
LM2651MTC-3.3
LM2651MTCX-3.3
ADJ
LM2651MTC-ADJ
LM2651MTCX-ADJ
Pin Description
Pin
Name
Function
1, 2
SW
Switched-node connection, which is connected with the source of the internal high-side
MOSFET.
3-5
VIN
Main power supply pin.
6
VCB
Bootstrap capacitor connection for high-side gate drive.
7
AVIN
Input supply voltage for control and driver circuits.
8
SD(SS)
Shutdown control input, active low. This pin can also function as soft-start control pin. A
capacitor connected from this pin to ground sets the ramp time to full current output.
9
FB
Output voltage feedback input. Connected to the output voltage.
10
COMP
Compensation network connection. Connected to the output of the voltage error
amplifier.
11
NC
No internal connection.
12-13
AGND
Low-noise analog ground.
14-16
PGND
Power ground.
16-Lead TSSOP (MTC)
DS100925-2
LM2651
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2
Absolute Maximum Ratings
(Note 1)
If Military/Aerospace specified devices are required,
please contact the National Semiconductor Sales Office/
Distributors for availability and specifications.
Input Voltage
15V
Feedback Pin Voltage
-0.4V
V
FB
5V
Power Dissipation (T
A
=25C),
(Note 2)
893 mW
Junction Temperature Range
-40C
T
J
+125C
Storage Temperature Range
-65C to +150C
ESD Susceptibility
Human Body Model (Note 3)
1kV
Operating Ratings
(Note 1)
Supply Voltage
4V
V
IN
14V
Electrical Characteristics
Specifications in standard type face are for T
J
= 25C and those with boldface
type apply over full operating junction temperature range. V
IN
=10V unless otherwise specified.
LM2651-1.8 System Parameters
Symbol
Parameter
Conditions
Typical
Limit
Units
V
OUT
Output Voltage
I
LOAD
= 900 mA
1.8
1.761/1.719
1.836/1.854
V
V(min)
V(max)
V
OUT
Output Voltage Line
Regulation
V
IN
= 4V to 14V
I
LOAD
= 900 mA
0.2
%
V
OUT
Output Voltage Load
Regulation
I
LOAD
= 10 mA to 1.5A
V
IN
= 5V
1.3
%
V
OUT
Output Voltage Load
Regulation
I
LOAD
= 200 mA to 1.5A
V
IN
= 5V
0.3
%
V
HYST
Sleep Mode Output Voltage
Hysteresis
35
mV
LM2651-2.5 System Parameters
Symbol
Parameter
Conditions
Typical
Limit
Units
V
OUT
Output Voltage
I
LOAD
= 900 mA
2.5
2.43/2.388
2.574/2.575
V
V(min)
V(max)
V
OUT
Output Voltage Line
Regulation
V
IN
= 4V to 12V
I
LOAD
= 900 mA
0.2
%
V
OUT
Output Voltage Load
Regulation
I
LOAD
= 10 mA to 1.5A
V
IN
= 5V
1.3
%
V
OUT
Output Voltage Load
Regulation
I
LOAD
= 200 mA to 1.5A
V
IN
= 5V
0.3
%
V
HYST
Sleep Mode Output Voltage
Hysteresis
48
mV
LM2651-3.3 System Parameters
Symbol
Parameter
Conditions
Typical
Limit
Units
V
OUT
Output Voltage
I
LOAD
= 900 mA
3.3
3.265/3.201
3.379/3.399
V
V(min)
V(max)
V
OUT
Output Voltage Line
Regulation
V
IN
= 4V to 14V
I
LOAD
= 900 mA
0.2
%
V
OUT
Output Voltage Load
Regulation
I
LOAD
= 10 mA to 1.5A
V
IN
= 5V
1.3
%
V
OUT
Output Voltage Load
Regulation
I
LOAD
= 200 mA to 1.5A
V
IN
= 5V
0.3
%
LM2651
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3
LM2651-3.3 System Parameters
(Continued)
Symbol
Parameter
Conditions
Typical
Limit
Units
V
HYST
Sleep Mode Output Voltage
Hysteresis
60
mV
LM2651-ADJ System Parameters
(V
OUT
= 2.5V unless otherwise specified)
Symbol
Parameter
Conditions
Typical
Limit
Units
V
FB
Feedback Voltage
I
LOAD
= 900 mA
1.238
1.200
1.263
V
V(min)
V(max)
V
OUT
Output Voltage Line
Regulation
V
IN
= 4V to 14V
I
LOAD
= 900 mA
0.2
%
V
OUT
Output Voltage Load
Regulation
I
LOAD
= 10 mA to 1.5A
V
IN
= 5V
1.3
%
V
OUT
Output Voltage Load
Regulation
I
LOAD
= 200 mA to 1.5A
V
IN
= 5V
0.3
%
V
HYST
Sleep Mode Output Voltage
Hysteresis
24
mV
All Output Voltage Versions
Specifications in standard type face are for T
J
= 25C and those with boldface type apply over full operating junction tem-
perature range. V
IN
=10V unless otherwise specified.
Symbol
Parameter
Conditions
Typical
Limit
Units
I
Q
Quiescent Current
1.6
2.0
mA
mA(max)
I
QSD
Quiescent Current in
Shutdown Mode
Shutdown Pin Pulled Low
7
12/20
A
A(max)
R
SW(ON)
High-Side or Low-Side
Switch On Resistance
(MOSFET On Resistance +
Bonding Wire Resistance)
I
SWITCH
= 1A
110
m
R
DS(ON)
MOSFET On Resistance
(High-Side or Low-Side)
I
SWITCH
= 1A
75
130
m
m
(max)
I
L
Switch Leakage Current -
High Side
130
nA
Switch Leakage Current -
Low Side
130
nA
V
BOOT
Bootstrap Regulator Voltage
I
BOOT
= 1 mA
6.75
6.45/6.40
6.95/7.00
V
V(min)
V(max)
G
M
Error Amplifier
Transconductance
1250
mho
V
INUV
V
IN
Undervoltage Lockout
Threshold Voltage
Rising Edge
3.8
3.95
V
V(max)
V
UV-HYST
Hysteresis for the
Undervoltage Lockout
210
mV
I
CL
Switch Current Limit
V
IN
= 5V
2
1.55
2.60
A
A(min)
A(max)
I
SM
Sleep Mode Threshold
Current
V
IN
= 5V
100
mA
A
V
Error Amplifier Voltage Gain
100
V/V
LM2651
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All Output Voltage Versions
(Continued)
Specifications in standard type face are for T
J
= 25C and those with boldface type apply over full operating junction tem-
perature range. V
IN
=10V unless otherwise specified.
Symbol
Parameter
Conditions
Typical
Limit
Units
I
EA_SOURCE
Error Amplifier Source
Current
40
25/15
A
A(min)
I
EA_SINK
Error Amplifier Sink Current
65
30
A
A(min)
V
EAH
Error Amplifier Output Swing
Upper Limit
2.70
2.50/2.40
V
V(min)
V
EAL
Error Amplifier Output Swing
Lower Limit
1.25
1.35/1.50
V
V(max)
V
D
Body Diode Voltage
I
DIODE
= 1.5A
1
V
f
OSC
Oscillator Frequency
V
IN
= 4V
300
280/255
330/345
kHz
kHz(min)
kHz(max)
D
MAX
Maximum Duty Cycle
V
IN
= 4V
95
92
%
%(min)
I
SS
Soft-Start Current
Voltage at the SS pin = 1.4V
11
7
14
A
A(min)
A(max)
I
SHUTDOWN
Shutdown Pin Current
Shutdown Pin Pulled Low
2.2
0.8/0.5
3.7/4.0
A
A(min)
A(max)
v
SHUTDOWN
Shutdown Pin Threshold
Voltage
Falling Edge
0.6
0.3
0.9
V
V(min)
V(max)
T
SD
Thermal Shutdown
Temperature
165
C
T
SD_HYST
Thermal Shutdown
Hysteresis Temperature
25
C
Note 1: Absolute maximum ratings indicate limits beyond which damage to the device may occur. Operating ratings indicate conditions for which the device is in-
tended to be functional, but device parameter specifications may not be guaranteed under these conditions. For guaranteed specifications and test conditions, see
the Electrical Characteristics.
Note 2: The maximum allowable power dissipation is calculated by using P
Dmax
= (T
Jmax
- T
A
)/
JA
, where T
Jmax
is the maximum junction temperature, T
A
is the
ambient temperature, and
JA
is the junction-to-ambient thermal resistance of the specified package. The 893 mW rating results from using 150C, 25C, and
140C/W for T
Jmax
, T
A
, and
JA
respectively. A
JA
of 140C/W represents the worst-case condition of no heat sinking of the 16-pin TSSOP package. Heat sinking
allows the safe dissipation of more power. The Absolute Maximum power dissipation must be derated by 7.14mW per C above 25C ambient. The LM2651 actively
limits its junction temperature to about 165C.
Note 3: The human body model is a 100pF capacitor discharged through a 1.5k
resistor into each pin.
Note 4: Typical numbers are at 25C and represent the most likely norm.
Note 5: All limits are guaranteed at room temperature (standard typeface) and at temperature extremes (boldface type ). All room temperature limits are 100%
production tested. All limits at temperature extremes are guaranteed via correlation using standard Statistical Quality Control (SQC) methods. All limits are used to
calculate Average Outgoing Quality Level (AOQL).
LM2651
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