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February 2000
LM2655
2.5A High Efficiency Synchronous Switching Regulator
LM2655 2.5A High Efficiency Synchronous Switching Regulator
General Description
The LM2655 is a current-mode controlled PWM step-down
switching regulator. It has the unique ability to operate in
synchronous or asynchronous mode. This gives the designer flexibility to choose between the high efficiency of
synchronous operation, or the low solution cost of asynchronous operation. Along with flexibility, the LM2655 offers high
power density with the small footprint of a TSSOP-16 package.
High efficiency (
ternal low ON-resistance (33mΩ) MOSFET, and an external
N-Channel MOSFET. This feature, together with its low quiescent current, makesthe LM2655 an ideal fit in portable applications.
Integrated in the LM2655 are all the power,control, and drive
functions for asynchronous operation. In addition, a low-side
driver output allows easy synchronous operation. The IC
uses patented current sensing circuitry that eliminates the
external current sensing resistor required by other currentmode DC-DC converters. A programmable soft-start feature
limits start up current surges and provides a means of sequencing multiple power supplies.
>
90%) is obtained through the use of an in-
Typical Application
Features
n Ultra-high efficiency up to 96
n 4V to 14V input voltage range
n Internal high-side MOSFET with low R
n 300 kHz fixed frequency internal oscillator
n Low-side drive for synchronous operation
n Guaranteed less than 12 µA shutdown current
n Patented current sensing for current mode control
n Programmable soft-start
n Input undervoltage lockout
n Output overvoltage shutdown protection
n Output undervoltage shutdown protection
n Thermal Shutdown
n 16-pin TSSOP package
%
= 0.033Ω
DS(ON)
Applications
n Hard disk drives
n Internet appliances
n TFT monitors
n Computer peripherals
n Battery powered devices
DS101284-29
© 2000 National Semiconductor Corporation DS101284 www.national.com
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Connection Diagram
LM2655
Block Diagram
16-Lead TSSOP (MTC)
DS101284-3
Top View
Order Number LM2655MTC-ADJ
See NS Package Number MTC16
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DS101284-4
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Pin Description
Pin Name Function
1-2 SW Switched-node connection, which is connected to the source of the internal high-side
MOSFET.
3-5 PV
6V
7AV
IN
CB
IN
8 SD(SS)
Main power supply input pin. Connected to the drain of the internal high-side MOSFET.
Bootstrap capacitor connection for high-side gate drive.
Input voltage for control and drive circuits.
Shutdown control input, active low. This pin can also function as soft-start control pin.
Connect a capacitor from this pin to ground.
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 L
DELAY
A capacitor between this pin to ground sets the delay from when the output voltage
reaches 80%of its nominal to when the undervoltage latch protection is enabled.
12 LDR Low-side FET gate drive pin.
13 GND Power ground.
14-16 PV
IN
Main power supply input pin. Connected to the drain of the internal high-side MOSFET.
Ordering Information
LM2655
Supplied as 1000 units
Tape and Reel
Supplied as 3000 units,
Tape and Reel
LM2655MTC-3.3 LM2655MTCX-3.3
LM2655MTC-ADJ LM2655MTCX-ADJ
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Absolute Maximum Ratings (Note 1)
If Military/Aerospace specified devices are required,
LM2655
please contact the National Semiconductor Sales Office/
Distributors for availability and specifications.
Supply Voltage (PV
Supply Voltage (AV
) 3.8V ≤ VIN≤ 14V
IN
) 4.0V ≤ VIN≤ 14V
IN
Feedback Pin Voltage -0.4V ≤ V
V
Voltage, (Note 7) 7V
CB
C
Voltage 2.5V
SS
Comp Voltage 2.5V
L
Voltage 2.5V
DELAY
LDR Voltage 5V
V
, (Note 8) 14V
SW
LM2655-3.3 Electrical Characteristics
Specifications with standard typeface are for T
Range.V
=
10V unless otherwise specified.
IN
Symbol Parameter Conditions
V
OUT
V
OUT
Output Voltage I
Output Voltage Line
Regulation
Output Voltage Load
Regulation
V
INUV
VINUndervoltage Lockout
Threshold Voltage
V
UV_HYST
Hysteresis for the Input
Undervoltage Lockout
I
(Note 9) Average Output Current
CL
Limit
=
J
LOAD
V
I
LOAD
I
LOAD
V
Rising Edge 3.8
V
V
=
Power Dissipation (T
A
25˚C),
(Note 2)
TSSOP-16 Package θ
JA
140˚C/W
Power Dissapation 893mW
Lead Temperature
Vapor Phase (60 sec.) 215˚C
≤ 5V
FB
Infrared (15 sec.) 220˚C
ESD Susceptibility(Note 3)
Human Body Model(Note 4) 1kV
Machine Model 200V
Operating Ratings (Note 1)
Storage Temperature Range −65˚C ≤ T
Junction Temperature
Range −40˚C ≤ T
25˚C, and those in boldface type apply over full Operating Temperature
=
1.5 A 3.3
Typical
(Note 5)
Limit
(Note 6)
3.235/3.185
3.392/3.416
=
IN
=
IN
5V to 14V
=
=
10V
1.5 A
100 mA to 2.5A
0.5
0.7
0.6
1.7
3.95
210 mV
IN
OUT
=
5V
=
3.3V
3.3
≤ +150˚C
J
≤ +125˚C
J
Units
V(min)
V(max)
%
%
V(max)
V
%
(max)
%
(max)
V
A
LM2655-ADJ Electrical Characteristics
Specifications with standard typeface are for T
Range.V
=
10V unless otherwise specified.
IN
Symbol Parameter Conditions
V
FB
V
OUT
Feedback Voltage I
Output Voltage Line
Regulation
Output Voltage Load
Regulation
V
INUV
VINUndervoltage Lockout
Threshold Voltage
V
UV_HYST
Hysteresis for the Input
Undervoltage Lockout
I
(Note 9) Average Output Current
CL
Limit
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=
25˚C, and those in boldface type apply over full Operating Temperature
J
=
1.5 A 1.238
LOAD
=
V
5V to 14V
IN
=
LOAD
LOAD
IN
=
=
10V
1.5 A
100 mA to 2.5A
I
I
V
Rising Edge 3.8
=
V
5V
IN
=
OUT
3.3V
V
Typical
(Note 5)
Limit
(Note 6)
1.208/1.181
1.260/1.267
0.5
0.7
0.6
1.7
3.95
210 mV
3.3 A
Units
V
V(min)
V(max)
%
%
(max)
%
%
(max)
V
V(max)
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All Output Voltage Versions Electrical Characteristics
Specifications with standard typeface are for T
Range.V
=
10V unless otherwise specified.
IN
Symbol Parameter Conditions
I
I
Q
QSD
Quiescent Current Shutdown Pin Floating (Device On)
Quiescent Current in
Shutdown Mode
R
DS(ON)
R
SW(ON)
Switch ON Resistance I
Switch On Resistance
(MOSFET ON Resistance
+ Bonding Wire
Resistance)
I
V
L
BOOT
Switch Leakage Current 5 nA
Bootstrap Regulator
Voltage
G
M
Error Amplifier
Transconductance
A
V
Error Amplifier Voltage
Gain
I
EA_SOURCE
Error Amplifier Source
Current
I
EA_SINK
V
EAH
Error Amplifier Sink Current VIN= 4V, VFB= 1.1*V
Error Amplifier Output
Swing Upper Limit
V
EAL
Error Amplifier Output
Swing Lower Limit
F
OSC
D
I
SS
V
MAX
OUTUV
Oscillator Frequency Measured at Switch Pin
Maximum Duty Cycle VIN=4V 95
Soft-Start Current Voltage at the SS Pin = 1.4V 11
V
Undervoltage
OUT
Lockout Threshold Voltage
V
OUTOV
Hysteresis for V
V
Overvoltage Lockout
OUT
OUTUV
Threshold Voltage
Hysteresis for V
I
LDELAY__
SOURCE
I
SHUTDOWN
V
SHUTDOWN
LDELAY Pin Source
Current
Shutdown Pin Current Shutdown Pin Pulled Low 2.2
Shutdown Pin Threshold
OUTOV
Voltage
T
SD
Thermal Shutdown
Temperature
T
SD_HYST
Thermal Shutdown
Hysteresis Temperature
=
25˚C, and those in boldface type apply over full Operating Temperature
J
Device Not Switching
Shutdown Pin Pulled Low 7
= 1.5A 33
SWITCH
I
I
C
VIN= 4V, VFB= .9*V
= 1.5A 72 mΩ
SWITCH
=1mA
BOOT
=tbd
BOOT
OUT,VCOMP
=
2V
OUT,VCOMP
=
2V
VIN= 4V, VFB= .9*V
OUT,VCOMP
=
2V
VIN= 4V, VFB= .9*V
OUT,VCOMP
=
2V
=4V
V
IN
Rising Edge 0.6
LM2655
Typical
(Note 6)
1.7
6.7
1250 µmho
100
40
80
2.70
1.25
300
81
5
108
5
5µA
165 ˚C
25 ˚C
Limit
(Note 5)
3
12/20
80
6.4
7.0
32/10
53/30
2.50/2.40
1.35/1.50
280/255
330/345
92
14
76
84
106
114
3.7/4.0
0.25
0.9
Units
mA
mA(max)
µA
µA(max)
mΩ
mΩ(max)
V
V(min)
V(max)
µA
µA(min)
µA
µA(min)
V
V(min)
V
V(max)
kHz
kHz(min)
kHz(max)
%
%
(min)
µA
µA(max)
%
V
%
V
OUT
%
V
OUT
%
V
%
V
%
V
OUT
%
V
OUT
%
V
µA
µA(max)
V
V(min)
V(max)
OUT
(min)
(max)
OUT
OUT
(min)
(max)
OUT
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