Interseal LM2703MF SERVICE MANUAL X7

February 2002

LM2703
Micropower Step-up DC/DC Converter with 350mA Peak
Current Limit

LM2703 Micropower Step-up DC/DC Converter with 350mA Peak Current Limit

General Description

The LM2703 is a micropower step-up DC/DC in a small
5-lead SOT-23 package. A current limited, fixed off-time
control scheme conserves operating current resulting in high
efficiency over a wide range of load conditions. The 21V
switch allows for output voltages as high as 20V. The low
400ns off-time permits the use of tiny, low profile inductors
and capacitors to minimize footprint and cost in
space-conscious portable applications. The LM2703 is ideal
for LCD panels requiring low current and high efficiency as
well as white LED applications for cellular phone
back-lighting. The LM2703 can drive up to 4 white LEDs
from a single Li-Ion battery.

Typical Application Circuit

Features

n 350mA, 0.7Ω, internal switch
n Uses small surface mount components
n Adjustable output voltage up to 20V
n 2.2V to 7V input range
n Input undervoltage lockout
n 0.01µA shutdown current
n Small 5-Lead SOT-23 package

Applications

n LCD Bias Supplies
n White LED Back-Lighting
n Handheld Devices
n Digital Cameras
n Portable Applications

20030601

FIGURE 1. Typical 20V Application

© 2002 National Semiconductor Corporation DS200306 www.national.com

Connection Diagram

LM2703

Top View

SOT23-5

T

= 125˚C, θJA= 220˚C/W (Note 2)

Jmax

20030602

Ordering Information

Order Number Package Type NSC Package Drawing Supplied As

LM2703MF-ADJ SOT23-5 MA05B 1000 Units, Tape and Reel

LM2703MFX-ADJ SOT23-5 MA05B 3000 Units, Tape and Reel

Pin Description/Functions

Pin Name Function

1 SW Power Switch input.
2 GND Ground.
3 FB Output voltage feedback input.
4 SHDN
5V

SW(Pin 1): Switch Pin. This is the drain of the internal
NMOS power switch. Minimize the metal trace area con­nected to this pin to minimize EMI.

GND(Pin 2): Ground Pin. Tie directly to ground plane.
FB(Pin 3): FeedbackPin.Set the output voltage by selecting

values for R1 and R2 using:

IN

Shutdown control input, active low.
Analog and Power input.

Connect the ground of the feedback network to an AGND
plane which should be tied directly to the GND pin.

SHDN(Pin 4): Shutdown Pin. The shutdown pin is an active
low control. Tie this pin above 1.1V to enable the device. Tie
this pin below 0.3V to turn off the device.

V

IN

as close to the device as possible.

(Pin 5): Input Supply Pin. Bypass this pin with a capacitor

www.national.com 2

LM2703

Absolute Maximum Ratings (Note 1)

If Military/Aerospace specified devices are required,
please contact the National Semiconductor Sales Office/
Distributors for availability and specifications.

V

IN

7.5V

Infrared
(15 sec.) 220˚C

ESD Ratings (Note 3)

Human Body Model
Machine Model (Note 4)

200V

SW Voltage 21V
FB Voltage 2V
SHDN Voltage
Maximum Junction Temp. T

J

7.5V

150˚C

(Note 2)
Lead Temperature

(Soldering 10 sec.) 300˚C

Operating Conditions

Junction Temperature
(Note 5) −40˚C to +125˚C

Supply Voltage 2.2V to 7V
SW Voltage Max. 20.5V

Vapor Phase
(60 sec.) 215˚C

Electrical Characteristics

Specifications in standard type face are for TJ= 25˚C and those in boldface type apply over the full Operating Temperature
Range (T

Symbol Parameter Conditions

I

Q

V

FB

I

CL

I

B

V

IN

R

DSON

T

OFF

I

SD

I

L

UVP Input Undervoltage Lockout ON/OFF Threshold 1.8 V
V

FB

Hysteresis
SHDN

Threshold

θ

JA

Note 1: Absolute maximum ratings are limits beyond which damage to the device may occur. Operating Ratings are conditions for which the device is intended to
be functional, but device parameter specifications may not be guaranteed. For guaranteed specifications and test conditions, see the Electrical Characteristics.

Note 2: The maximum allowable power dissipation is a function of the maximum junction temperature, T
and the ambient temperature, T
temperature is calculated using: P

Note 3: The human body model is a 100 pF capacitor discharged through a 1.5 kΩ resistor into each pin. The machine model is a 200 pF capacitor discharged
directly into each pin.

Note 4: ESD susceptibility using the machine model is 150V for SW pin.
Note 5: All limits guaranteed at room temperature (standard typeface) and at temperature extremes (bold typeface). All room temperature limits are 100%

production tested or guaranteed through statistical analysis. 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).

Note 6: Typical numbers are at 25˚C and represent the most likely norm.
Note 7: Feedback current flows into the pin.

= −40˚C to +125˚C). Unless otherwise specified. VIN=2.2V.

J

Min

(Note 5)

Typ

(Note 6)

Max

(Note 5)

Device Disabled FB = 1.3V 40 70

Shutdown SHDN = 0V

0.01 2.5
FeedbackTrip Point 1.189 1.237 1.269 V
Switch Current Limit 275

260

350 400

400

FB Pin Bias Current FB = 1.23V (Note 7) 30 120 nA
Input Voltage Range 2.2 7.0 V
Switch R

DSON

0.7 1.6 Ω
Switch Off Time 400 ns
SHDN Pin Current SHDN = VIN,TJ= 25˚C 080

= 125˚C 15

IN,TJ

SHDN = GND

0

Switch Leakage Current VSW= 20V 0.05 5 µA

Feedback Hysteresis 8 mV

SHDN low
SHDN High

1.1 0.7

0.7 0.3

Thermal Resistance 220 ˚C/W

(MAX), the junction-to-ambient thermal resistance, θJA,

. See the Electrical Characteristics table for the thermal resistance. The maximum allowable power dissipation at any ambient

A

(MAX) = (T

D

J(MAX)−TA

)/θJA. Exceeding the maximum allowable power dissipation will cause excessive die temperature.

J

Units

mA

2kV

µADevice Enabled FB = 1.2V 235 300

nASHDN = V

V

www.national.com3

Typical Performance Characteristics

LM2703

Enable Current vs V

IN

(Part Switching)

20030605 20030606

Efficiency vs Load Current Efficiency vs Load Current

Disable Current vs V

(Part Not Switching)

IN

20030610

Efficiency vs Load Current SHDN Threshold vs V

20030612

20030611

IN

20030613

www.national.com 4

Typical Performance Characteristics (Continued)

LM2703

Switch Current Limit vs V

IN

20030614 20030615

Switch R

DSON

vs V

IN

FB Trip Point and FB Pin Current vs Temperature Output Voltage vs Load Current

Step Response Start-Up/Shutdown

V

= 20V, VIN= 2.5V

OUT

1) Load, 1mA to 10mA to 1mA, DC

2) V

, 200mV/div, AC

OUT

3) I

, 200mA/div, DC

L

T = 50µs/div

20030623

20030616

V

= 20V, VIN= 2.5V

OUT

1) SHDN, 1V/div, DC

2) IL, 200mA/div, DC

3) V

, 20V/div, DC

OUT

T = 400µs/div
R

= 1.8kΩ

L

20030622

20030617

www.national.com5

Operation

LM2703

V

= 20V, VIN= 2.5V

OUT

1) V

, 20V/div, DC

SW

2) Inductor Current, 200mA/div, DC

3) V

, 200mV/div, AC

OUT

T = 4µs/div

20030604

FIGURE 2. LM2703 Block Diagram

20030618

FIGURE 3. Typical Switching Waveform

www.national.com 6

Operation (Continued)

The LM2703 features a constant off-time control scheme.
Operation can be best understood by referring to
and

Figure 3

R4 of

. Transistors Q1 and Q2 and resistors R3 and

Figure 2

form a bandgap reference used to control the

Figure 2

output voltage. When the voltage at the FB pin is less than

1.237V, the Enable Comp in

Figure 2

enables the device and
the NMOS switch is turned on pulling the SW pin to ground.
When the NMOS switch is on, current begins to flow through
inductor L while the load current is supplied by the output
capacitor C

. Once the current in the inductor reaches the

OUT

current limit, the CL Comp trips and the 400ns One Shot
turns off the NMOS switch.The SW voltage will then rise to
the output voltage plus a diode drop and the inductor current
will begin to decrease as shown in
the energy stored in the inductor is transferred to C

Figure 3

. During this time

and

OUT

the load. After the 400ns off-time the NMOS switch is turned
on and energy is stored in the inductor again. This energy
transfer from the inductor to the output causes a stepping
effect in the output ripple as shown in

Figure 3

.

This cycle is continued until the voltage at FB reaches

1.237V. When FB reaches this voltage, the enable compara­tor then disables the device turning off the NMOS switch and
reducing the Iq of the device to 40uA. The load current is
then supplied solely by C
decreasing slope at the output as shown in

indicated by the gradually

OUT

Figure 3

. When
the FB pin drops slightly below 1.237V, the enable compara­tor enables the device and begins the cycle described pre­viously. The SHDN pin can be used to turn off the LM2703
and reduce the Iqto 0.01µA. In shutdown mode the output
voltage will be a diode drop lower than the input voltage.

Application Information

Inductor Selection

The appropriate inductor for a given application is calculated
using the following equation:

where VDis the schottky diode voltage, ICLis the switch
current limit found in the

tics

section, and T
equation be sure to use the minimum input voltage for the
application, such as for battery powered applications. For
the LM2703 constant-off time control scheme, the NMOS
power switch is turned off when the current limit is reached.
There is approximately a 200ns delay from the time the
current limit is reached in the NMOS power switch and when
the internal logic actually turns off the switch. During this
200ns delay, the peak inductor current will increase. This
increase in inductor current demands a larger saturation
current rating for the inductor. This saturation current can be
approximated by the following equation:

Typical Performance Characteris-

is the switch off time. When using this

OFF

Choosing inductors with low ESR decrease power losses
and increase efficiency.

Care should be taken when choosing an inductor. For appli­cations that require an input voltage that approaches the
output voltage, such as when converting a Li-Ion battery
voltage to 5V, the 400ns off time may not be enough time to
discharge the energy in the inductor and transfer the energy
to the output capacitor and load. This can cause a ramping
effect in the inductor current waveform and an increased
ripple on the output voltage. Using a smaller inductor will
cause the I

to increase and will increase the output voltage

PK

ripple further. This can be solved by adding a 4.7pF capaci­tor across the R

feedback resistor (

F1

Figure 2

) and slightly
increasing the output capacitor. A smaller inductor can then
be used to ensure proper discharge in the 400ns off time.

Diode Selection

To maintain high efficiency, the average current rating of the
schottky diode should be larger than the peak inductor cur­rent, I

. Schottky diodes with a low forward drop and fast

PK

switching speeds are ideal for increasing efficiency in por­table applications. Choose a reverse breakdown of the
schottky diode larger than the output voltage.

Capacitor Selection

Choose low ESR capacitors for the output to minimize output
voltage ripple. Multilayer ceramic capacitors are the best
choice. For most applications, a 1µF ceramic capacitor is
sufficient. For some applications a reduction in output volt­age ripple can be achieved by increasing the output capaci­tor.

Local bypassing for the input is needed on the LM2703.
Multilayer ceramic capacitors are a good choice for this as
well.A 4.7µF capacitor is sufficient for most applications. For
additional bypassing, a 100nF ceramic capacitor can be
used to shunt high frequency ripple on the input.

Layout Considerations

The input bypass capacitor C

, as shown in

IN

Figure 1

, must
be placed close to the IC. This will reduce copper trace
resistance which effects input voltage ripple of the IC. For
additional input voltage filtering, a 100nF bypass capacitor
can be placed in parallel with C
quency noise to ground. The output capacitor, C

to shunt any high fre-

IN

OUT

, should
also be placed close to the IC.Any copper trace connections
for the Cout capacitor can increase the series resistance,
which directly effects output voltage ripple. The feedback
network, resistors R1 and R2, should be kept close to the FB
pin to minimize copper trace connections that can inject
noise into the system. The ground connection for the feed­back resistor network should connect directly to an analog
ground plane. The analog ground plane should tie directly to
the GND pin. If no analog ground plane is available, the
ground connection for the feedback network should tie di­rectly to the GND pin. Trace connections made to the induc­tor and schottky diode should be minimized to reduce power
dissipation and increase overall efficiency.

LM2703

www.national.com7

Application Information (Continued)

LM2703

20030609

FIGURE 4. White LED Application

FIGURE 5. Li-Ion 5V Application

FIGURE 6. Li-Ion 12V Application

www.national.com 8

20030619

20030620

Application Information (Continued)

FIGURE 7. 5V to 12V Application

LM2703

20030621

www.national.com9

Physical Dimensions inches (millimeters)

unless otherwise noted

5-Lead Small Outline Package (M5)

For Ordering, Refer to Ordering Information Table

NS Package Number MA05B

LIFE SUPPORT POLICY

NATIONAL’S PRODUCTS ARE NOT AUTHORIZED FOR USE AS CRITICAL COMPONENTS IN LIFE SUPPORT
DEVICES OR SYSTEMS WITHOUT THE EXPRESS WRITTEN APPROVAL OF THE PRESIDENT AND GENERAL
COUNSEL OF NATIONAL SEMICONDUCTOR CORPORATION. As used herein:

LM2703 Micropower Step-up DC/DC Converter with 350mA Peak Current Limit

1. Life support devices or systems are devices or
systems which, (a) are intended for surgical implant
into the body, or (b) support or sustain life, and
whose failure to perform when properly used in
accordance with instructions for use provided in the

2. A critical component is any component of a life
support device or system whose failure to perform
can be reasonably expected to cause the failure of
the life support device or system, or to affect its
safety or effectiveness.

labeling, can be reasonably expected to result in a
significant injury to the user.

National Semiconductor
Corporation

Americas
Email: [e-mail]

www.national.com

National does not assume any responsibility for use of any circuitry described, no circuit patent licenses are implied and National reserves the right at any time without notice to change said circuitry and specifications.

National Semiconductor
Europe

Fax: [phone]

Email: [e-mail]
Deutsch Tel: [phone]
English Tel: [phone]
Français Tel: [phone]

National Semiconductor
Asia Pacific Customer
Response Group

Tel: [phone]
Fax: [phone]
Email: [e-mail]

National Semiconductor
Japan Ltd.

Tel: [phone]
Fax: [phone]