National Semiconductor LM2655 Technical data

April 2005

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 (
internal low ON-resistance (33mΩ) MOSFET, and an exter­nal N-Channel MOSFET. This feature, together with its low
quiescent current, makes the 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

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

DS(ON)

= 0.033Ω

Applications

n Hard disk drives
n Internet appliances
n TFT monitors
n Computer peripherals
n Battery powered devices

10128429

© 2005 National Semiconductor Corporation DS101284 www.national.com

Connection Diagram

LM2655

16-Lead TSSOP (MTC)

Block Diagram

Top View

10128403

Order Number LM2655MTC-ADJ

See NS Package Number MTC16

www.national.com 2

10128404

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 and Soft-start control pin. Pulling this pin below 0.3V shuts off the regulator. A
capacitor connected from this pin to ground provides a control ramp of the input current.
Do not drive this pin with an external source or erroneous operation may result.

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

www.national.com3

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

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

Power Dissipation (T

) 3.8V ≤ VIN≤ 14V

IN

) 4.0V ≤ VIN≤ 14V

IN

=25˚C),

A

≤ 5V

FB

TSSOP-16 Package θ

JA

Power Dissapation 893mW

Lead Temperature

Vapor Phase (60 sec.) 215˚C

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

(Note 2)

LM2655-3.3 Electrical Characteristics

Specifications with standard typeface are for TJ= 25˚C, and those in boldface type apply over full Operating Temperature
Range.V

Symbol Parameter Conditions

V

OUT

V

OUT

V

INUV

V

UV_HYST

ICL(Note 9) Average Output Current

= 10V unless otherwise specified.

IN

Output Voltage I

Output Voltage Line
Regulation

Output Voltage Load
Regulation

VINUndervoltage Lockout
Threshold Voltage

Hysteresis for the Input
Undervoltage Lockout

Limit

Typical

(Note 5)

= 1.5 A 3.3

LOAD

VIN=5Vto14V

= 1.5 A

I

LOAD

I

= 100 mA to 2.5A

LOAD

=10V

V

IN

0.5

0.6

Rising Edge 3.8

210 mV

VIN=5V

= 3.3V

V

OUT

3.3

Limit

(Note 6)

3.235/3.185

3.392/3.416

0.7

1.7

3.95

140˚C/W

≤ +150˚C

J

≤ +125˚C

J

Units

V

V(min)

V(max)

%

%(max)

%

%(max)

V

V(max)

LM2655-ADJ Electrical Characteristics

Specifications with standard typeface are for TJ= 25˚C, and those in boldface type apply over full Operating Temperature
Range.V

Symbol Parameter Conditions

V

FB

V

OUT

V

INUV

V

UV_HYST

(Note 9) Average Output Current

I

CL

www.national.com 4

= 10V unless otherwise specified.

IN

Feedback Voltage I

Output Voltage Line
Regulation

Output Voltage Load
Regulation

VINUndervoltage Lockout
Threshold Voltage

Hysteresis for the Input
Undervoltage Lockout

Limit

Typical

(Note 5)

= 1.5 A 1.238

LOAD

VIN=5Vto14V

= 1.5 A

I

LOAD

I

= 100 mA to 2.5A

LOAD

=10V

V

IN

0.5

0.6

Rising Edge 3.8

210 mV

VIN=5V

= 3.3V

V

OUT

3.3 A

Limit

(Note 6)

1.208/1.181

1.260/1.267

0.7

1.7

3.95

Units

V

V(min)

V(max)

%

%(max)

%

%(max)

V

V(max)

All Output Voltage Versions Electrical Characteristics

Specifications with standard typeface are for TJ= 25˚C, and those in boldface type apply over full Operating Temperature
Range.V

Symbol Parameter Conditions

I

Q

I

QSD

R

DS(ON)

R

SW(ON)

I

L

V

BOOT

G

M

A

V

I

EA_SOURCE

I

EA_SINK

V

EAH

V

EAL

F

OSC

D

MAX

I

SS

V

OUTUV

V

OUTOV

I

LDELAY__

SOURCE

I

SHUTDOWN

V

SHUTDOWN

T

SD

= 10V unless otherwise specified.

IN

Quiescent Current Shutdown Pin Floating (Device

Typical

(Note 6)

1.7

Limit

(Note 5)

On)

Quiescent Current in
Shutdown Mode

Switch ON Resistance I

Device Not Switching

Shutdown Pin Pulled Low 7

= 1.5A 33

SWITCH

3

12/20

80

Switch On Resistance

I

= 1.5A 72 mΩ

SWITCH

(MOSFET ON Resistance +
Bonding Wire Resistance)

Switch Leakage Current 5 nA

Bootstrap Regulator Voltage I

BOOT

C

BOOT

=1mA

=tbd

6.7

6.4

7.0

Error Amplifier

1250 µmho

Transconductance

Error Amplifier Voltage Gain 100

Error Amplifier Source
Current

VIN= 4V, VFB= .9*V
=2V

OUT,VCOMP

Error Amplifier Sink Current VIN= 4V, VFB= 1.1*V

=2V

Error Amplifier Output Swing
Upper Limit

Error Amplifier Output Swing
Lower Limit

VIN= 4V, VFB= .9*V
=2V

VIN= 4V, VFB= .9*V
=2V

OUT,VCOMP

OUT,VCOMP

Oscillator Frequency Measured at Switch Pin

=4V

V

IN

OUT,VCOMP

40

32/10

80

53/30

2.70

2.50/2.40

1.25

1.35/1.50

300

280/255
330/345

Maximum Duty Cycle VIN=4V 95

92

Soft-Start Current Voltage at the SS Pin = 1.4V 11

14

V

Undervoltage Lockout

OUT

Threshold Voltage

81

76
84

Hysteresis for V

V

Overvoltage Lockout

OUT

OUTUV

Threshold Voltage

5%V

108

106
114

Hysteresis for V

OUTOV

5%V

LDELAY Pin Source Current 5 µA

Shutdown Pin Current Shutdown Pin Pulled Low 2.2

3.7/4.0

Shutdown Pin Threshold
Voltage

Rising Edge 0.6

0.25

0.9

Thermal Shutdown

165 ˚C

Temperature

Units

mA(max)

µA(max)

mΩ(max)

V(min)

V(max)

µA(min)

µA(min)

V(min)

V(max)

kHz

kHz(min)

kHz(max)

%(min)

µA(max)

%V

%V

OUT

%V

OUT

%V

%V

OUT

%V

OUT

µA(max)

V(min)

V(max)

LM2655

mA

µA

mΩ

V

µA

µA

V

V

%

µA

OUT

(min)

(max)

OUT

OUT

(min)

(max)

OUT

µA

V

www.national.com5