National Semiconductor LM3500 Technical data

December 2003

LM3500
Synchronous Step-up DC/DC Converter for White LED
Applications

Synchronous Step-up DC/DC Converter for White LED Applications

General Description

The LM3500 is a fixed frequency synchronous step-up
DC/DC converter in a small 8-bump thin micro SMD pack­age. The LM3500 is ideal for white LED applications for
cellular phone back-lighting requiring low current and high
efficiency. Its fixed 1MHz operating frequency allows the use
of small, low ESR capacitors as well as a more predictable
frequency spectrum, which is important in cellular phone
applications. The LM3500 can drive 2 to 4 white LEDs in
series from a single Li-Ion battery or 3 cell NiMH with no
external rectification diode. For white LED applications, a
single external resistor is used to set the maximum LED
current. The white LED current can easily be adjusted using
a pulse width modulated (PWM) signal on the shutdown pin.
The LM3500 uses special protection circuitry on the output
to prevent an overvoltage event if the primary white LED
network should be disconnected eliminating the need of an
extra protection Zener diode. In shutdown, the LM3500 dis­connects the input and output creating a true isolation pre­venting any LED light from emitting over the full input oper­ating voltage range and temperature.

Typical Application Circuit

Features

n Synchronous rectification, high efficiency and no

external schottky diode required

n Uses small surface mount components
n Can drive up to 3 (or 4 low V
n 2.7V to 7V input range
n True shutdown isolation
n Input undervoltage lockout
n Output overvoltage protection, no external zener diode

required

n Requires only a small 16V ceramic capacitor at the

output

n Thermal Shutdown
n 0.1µA shutdown current
n Small 8-bump thin micro SMD package

) white LEDs in series

F

Applications

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

20065701

FIGURE 1. Typical 3 LED Application

© 2003 National Semiconductor Corporation DS200657 www.national.com

Connection Diagram

LM3500

Top View

8-bump micro SMD

20065702

T

= 125˚C, θJA= 220˚C/W (Note 3)

J(MAX)

Ordering Information

Order Number Package Type NSC Package Drawing Top Mark Supplied As

LM3500TL-16 micro SMD TL08SSA C18 250 Units, Tape and Reel

LM3500TLX-16 micro SMD TL08SSA C18 3000 Units, Tape and Reel

Pin Description/Functions

Pin Name Function

A1 AGND Analog ground.

B1 V

C1 V

C2 V

IN

OUT

SW

C3 GND Power Ground.

B3 FB Output voltage feedback connection.

A3 NC No internal connection made to this pin.

A2 SHDN

AGND(pin A1): Analog ground pin. The analog ground pin
should tie directly to the GND pin.

V

(pin B1): Analog and Power supply pin. Bypass this pin

IN

with a capacitor, as close to the device as possible, con­nected between the V

(pin C1): Source connection of internal PMOS power

V

OUT

and GND pins.

IN

device. Connect the output capacitor between the V
GND pins as close as possible to the device.

(pin C2): Drain connection of internal NMOS and PMOS

V

SW

switch devices. Keep the inductor connection close to this
pin to minimize EMI radiation.

GND(pin C3): Power ground pin. Tie directly to ground
plane.

Analog and Power supply input.

PMOS source connection for synchronous rectification.

Switch pin. Drain connections of both NMOS and PMOS power devices.

Shutdown control pin.

FB(pin B3): Output voltage feedback connection. Set the
primary White LED network current with a resistor from the
FB pin to GND. Keep the current setting resistor close to the
device and connected between the FB and GND pins.

NC(pin A3): No internal connection is made to this pin. The
maximum allowable voltage that can be applied to this pin is

OUT

and

7.5V.
SHDN(pin A2): Shutdown control pin. Disable the device

with a voltage less than 0.3V and enable the device with a
voltage greater than 1.1V. The white LED current can be
controlled using a PWM signal at this pin. There is an
internal pull down on the SHDN pin, the device is in a
normally off state.

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LM3500

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

V

(Note 2) −0.3V to 16V

OUT

V

(Note 2) −0.3V to V

SW

FB Voltage −0.3V to 7.5V

SHDN Voltage

−0.3V to 7.5V

+0.3V

OUT

−0.3V to 7.5V

ESD Ratings (Note 4)

Human Body Model 2kV

Machine Model 200V

Operating Conditions

Junction Temperature
(Note 3) −40˚C to +125˚C

Supply Voltage 2.7V to 7V

NC −0.3V to 7.5V

Maximum Junction Temperature 150˚C

Lead Temperature
(Soldering 10 sec.) 300˚C

Vapor Phase

Thermal Properties

Junction to Ambient Thermal
Resistance (θ
SMD package (Note 3)

), 8-pin micro

JA

220˚C/W

(60 sec.) 215˚C

Infrared
(15 sec.) 220˚C

Electrical Characteristics

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

Symbol Parameter Conditions

I

Q

V

FB

∆V

FB

I

CL

I

B

V

IN

R

DSON

D

Limit

F

SW

I

SD

I

L

UVP Input Undervoltage Lockout ON Threshold 2.4 2.5 2.6

OVP Output Overvoltage

I

Vout

I

VL

= −10˚C to +85˚C. Unless otherwise specified VIN=2.7V.

A

Quiescent Current, Device

FB>0.54V

Not Switching

Quiescent Current, Device

FB=0V

Switching

Shutdown SHDN = 0V

Min

(Note 5)

Typ

(Note 6)

Max

(Note 5)

0.95 1.2

1.8 2.5

0.1 2 µA

FeedbackVoltage VIN= 2.7V to 7V 0.47 0.5 0.53 V

FeedbackVoltage Line
Regulation

Switch Current Limit VIN= 2.7V, Duty Cycle =

VIN= 2.7V to 7V

80%

= 3.0V, Duty Cycle =

V

IN

70%

0.1 0.4 %/V

275 400 480

255 400 530

FB Pin Bias Current FB = 0.5V (Note 7) 45 200 nA

Input Voltage Range 2.7 7.0 V

NMOS Switch R

PMOS Switch R

DSON

DSON

VIN= 2.7V, ISW= 300mA 0.43

V

= 6V, ISW= 300mA 1.1 2.3

OUT

Duty Cycle Limit FB = 0V 80 87 %

Switching Frequency 0.85 1.0 1.15 MHz

SHDN Pin Current (Note 8) SHDN = 5.5V 18 30

9 16

SHDN = GND

0.1

Switch Leakage Current VSW= 15V 0.01 0.5 µA

OFF Threshold 2.3 2.4 2.5

ON Threshold 15 15.5 16

Protection

V

Bias Current V

OUT

PMOS Switch Leakage
Current

OFF Threshold 14 14.6 15

= 15V, SHDN = V

OUT

V

= 15V, VSW=0V

OUT

IN

260 400 µA

0.01 3 µA

Units

mA

mA

Ω

µASHDN = 2.7V

V

V

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Electrical Characteristics (Continued)

Specifications in standard type face are for TA= 25˚C and those in boldface type apply over the Operating Temperature

LM3500

Range of T

Symbol Parameter Conditions

SHDN
Threshold

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

∆V

FB

I

CL

I

B

V

IN

R

DSON

D

Limit

F

SW

I

SD

I

L

UVP Input Undervoltage Lockout ON Threshold 2.4 2.5 2.6

OVP Output Overvoltage

I

Vout

I

VL

SHDN
Threshold

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: This condition applies if V

Note 3: The maximum allowable power dissipation is a function of the maximum operating junction temperature, T

resistance, θ
temperature is calculated using: P

Note 4: 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 5: All limits guaranteed at room temperature (standard typeface) and at temperature extremes (bold typeface). All room temperature limits are production
tested, guaranteed through statistical analysis or guaranteed by design. 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 out of the pin.

Note 8: Current flows into the pin.

= −10˚C to +85˚C. Unless otherwise specified VIN=2.7V.

A

SHDN low

SHDN High

= −40˚C to +125˚C). Unless otherwise specified VIN=2.7V.

J

Quiescent Current, Device

FB>0.54V

Not Switching

Quiescent Current, Device

FB=0V

Switching

Shutdown SHDN = 0V

Min

(Note 5)

1.1 0.65

Min

(Note 5)

Typ

(Note 6)

Max

(Note 5)

0.65 0.3

Typ

(Note 6)

Max

(Note 5)

0.95 1.2

1.8 2.5

0.1 2 µA

FeedbackVoltage VIN= 2.7V to 7V 0.47 0.5 0.53 V

FeedbackVoltage Line
Regulation

Switch Current Limit VIN= 3.0V, Duty Cycle =

VIN= 2.7V to 7V

70%

0.1 0.4 %/V

400 mA

FB Pin Bias Current FB = 0.5V (Note 7) 45 200 nA

Input Voltage Range 2.7 7.0 V

NMOS Switch R

PMOS Switch R

DSON

DSON

VIN= 2.7V, ISW= 300mA 0.43

V

= 6V, ISW= 300mA 1.1 2.3

OUT

Duty Cycle Limit FB = 0V 87 %

Switching Frequency 0.8 1.0 1.2 MHz

SHDN Pin Current (Note 8) SHDN = 5.5V 18 30

9 16

SHDN = GND

0.1

Switch Leakage Current VSW= 15V 0.01 0.5 µA

OFF Threshold 2.3 2.4 2.5

ON Threshold 15 15.5 16

Protection

V

Bias Current V

OUT

PMOS Switch Leakage
Current

SHDN low

SHDN High

<

V

IN

OUT

, and the ambient temperature, TA. See Thermal Properties for the thermal resistance. The maximum allowable power dissipation at any ambient

JA

(MAX) = (T

D

OFF Threshold 14 14.6 15

= 15V, SHDN = V

OUT

V

= 15V, VSW=0V

OUT

IN

260 400 µA

0.01 3 µA

0.65 0.3

1.1 0.65

>

.IfV

V

IN

J(MAX)−TA

, a voltage greater than VIN+ 0.3V should not be applied to the V

OUT

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

or VSWpins.

OUT

, the junction-to-ambient thermal

J(MAX)

Units

V

Units

mA

Ω

µASHDN = 2.7V

V

V

V

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Typical Performance Characteristics

LM3500

Switching Quiescent Current vs V

20065755 20065756

2 LED Efficiency vs LED Current

L = Coilcraft DT1608C-223,

Efficiency = 100*(P

IN

/(2V

LED*ILED

IN

Non-Switching Quiescent Current vs V

IN

2 LED Efficiency vs LED Current

L = TDK VLP4612T-220MR34,

))

Efficiency = 100*(PIN/(2V

LED*ILED

))

3 LED Efficiency vs LED Current

L = Coilcraft DT1608C-223,

Efficiency = 100*(P

IN

/(3V

LED*ILED

20065757

))

20065758

3 LED Efficiency vs LED Current

L = TDK VLP4612T-220MR34,

Efficiency = 100*(PIN/(3V

LED*ILED

20065779

))

20065780

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