National LM3500TL-16, LM3500TL-21 Schematic [ru]

February 2005

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

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

General Description

The LM3500 is a fixed-frequency step-up DC/DC converter
that is ideal for driving white LEDs for display backlighting and
other lighting functions. With fully intergrated synchronous
switching (no external schottky diode required) and a low
feedback voltage (500mV), power efficiency of the LM3500
circuit has been optimized for lighting applications in wireless
phones and other portable products (single cell Li-Ion or 3­cell NiMH battery supplies). The LM3500 operates with a fixed
1MHz switching frequency. When used with ceramic input
and output capacitors, the LM3500 provides a small, low­noise, low-cost solution.

Two LM3500 options are available with different output volt­age capabilities. The LM3500-21 has a maximum output
voltage of 21V and is typically suited for driving 4 or 5 white
LEDs in series. The LM3500-16 has a maximum output volt­age of 16V and is typically suited for driving 3 or 4 white LEDs
in series (maximum number of series LEDs dependent on
LED forward voltage). If the primary white LED network
should be disconnected, the LM3500 uses internal protection
circuitry on the output to prevent a destructive over-voltage
event.

A single external resistor is used to set the maximum LED
current in LED-drive applications. The LED current can easily
be adjusted using a pulse width modulated (PWM) signal on
the shutdown pin. In shutdown, the LM3500 completely dis­connects the input from output, creating total isolation and
preventing any leakage currents from trickling into the LEDs.

Features

Synchronous rectification, high efficiency and no external

■

schottky diode required
Uses small surface mount components

■

Can drive 2-5 white LEDs in series

■

(may function with more low-VF LEDs)

2.7V to 7V input range

■

Internal output over-voltage protection (OVP) circuitry,

■

with no external zener diode required
LM3500-16: 15.5V OVP; LM3500-21: 20.5V OVP.

True shutdown isolation

■

Input undervoltage lockout

■

Requires only small ceramic capacitors at the input and

■

output
Thermal Shutdown

■

0.1µA shutdown current

■

Small 8-bump thin micro SMD package

■

Applications

LCD Bias Supplies

■

White LED Backlighting

■

Handheld Devices

■

Digital Cameras

■

Portable Applications

■

Typical Application Circuit

20065701

© 2007 National Semiconductor Corporation 200657 www.national.com

Connection Diagram

LM3500

Top View

8-bump micro SMD

20065702

Ordering Information

Maximum

Output Voltage

16V LM3500TL-16 micro SMD TL08SSA S18 250 Units, Tape and Reel

16V LM3500TLX-16 micro SMD TL08SSA S18 3000 Units, Tape and Reel

21V LM3500TL-21 micro SMD TL08SSA S23 250 Units, Tape and Reel

21V LM3500TLX-21 micro SMD TL08SSA S23 3000 Units, Tape and Reel

Order Number Package Type NSC Package

Drawing

Top Mark Supplied As

Pin Description/Functions

Pin Name Function

A1 AGND Analog ground.

B1 V

C1 V

C2 V

C3 GND Power Ground.

B3 FB Output voltage feedback connection.

A3 NC No internal connection made to this pin.

A2 SHDN Shutdown control pin.

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

VIN(pin B1): Analog and Power supply pin. Bypass this pin
with a capacitor, as close to the device as possible, connected
between the VIN and GND pins.

V

(pin C1): Source connection of internal PMOS power

OUT

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

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

IN

OUT

SW

Analog and Power supply input.

PMOS source connection for synchronous rectification.

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

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.

www.national.com 2

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

(LM3500-16)(Note 2)

OUT

V

(LM3500-21)(Note 2)

OUT

VSW(Note 2) −0.3V to V

FB, SHDN, and NC Voltages −0.3V to 7.5V

−0.3V to 7.5V

−0.3V to 16V

−0.3V to 21V
+0.3V

OUT

Operating Conditions

Ambient Temperature
(Note 5) −40°C to +85°C

Junction Temperature −40°C to +125°C
Supply Voltage 2.7V to 7V

Thermal Properties

Junction to Ambient Thermal
Resistance (θJA)(Note 6)

75°C/W

Maximum Junction Temperature 150°C
Lead Temperature

(Note 3) 300°C
ESD Ratings (Note 4)
Human Body Model 2kV
Machine Model 200V

Electrical Characteristics

Specifications in standard type face are for TA = 25°C and those in boldface type apply over the Operating Temperature Range
of TA = −10°C to +85°C. Unless otherwise specified VIN =2.7V and specification apply to both LM3500-16 and LM3500-21.

Symbol Parameter Conditions

I

Q

Quiescent Current, Device Not
Switching

Quiescent Current, Device
Switching

FB > 0.54V

FB = 0V

Min

(Note 7)

Shutdown SHDN = 0V 0.1 2 µA

V

ΔV

FB

FB

Feedback Voltage VIN = 2.7V to 7V 0.47 0.5 0.53

Feedback Voltage Line

VIN = 2.7V to 7V

Regulation

I

CL

I

B

V

R

D

IN

DSON

Limit

Switch Current Limit
(LM3500-16)

Switch Current Limit
(LM3500-21)

VIN = 2.7V,
Duty Cycle = 80%

VIN = 3.0V,
Duty Cycle = 70%

VIN = 2.7V,
Duty Cycle = 70%

VIN = 3.0V,
Duty Cycle = 63%

275 400 480

255 400 530

420 640 770

450 670 800

FB Pin Bias Current FB = 0.5V (Note 9)

Input Voltage Range 2.7 7.0 V

NMOS Switch R

PMOS Switch R

DSON

DSON

VIN = 2.7V, ISW = 300mA

V

= 6V, ISW = 300mA

OUT

Duty Cycle Limit (LM3500-16) FB = 0V 80 87

Duty Cycle Limit (LM3500-21) FB = 0V 85 94

F

SW

I

SD

Switching Frequency

0.85 1.0 1.15 MHz

SHDN Pin Current (Note 10) SHDN = 5.5V 18 30

SHDN = GND 0.1

I

L

Switch Leakage Current

VSW = 15V 0.01 0.5 µA

(LM3500-16)

Switch Leakage Current

VSW = 20V 0.01 2.0

(LM3500-21)

UVP Input Undervoltage Lockout ON Threshold 2.4 2.5 2.6

OFF Threshold 2.3 2.4 2.5

Typ

(Note 8)

Max

(Note 7)

0.95 1.2

1.8 2.5

0.1 0.4 %/V

45 200 nA

0.43

1.1 2.3

Units

mA

V

mA

Ω

%

µASHDN = 2.7V 9 16

V

3 www.national.com

Symbol Parameter Conditions

LM3500

OVP Output Overvoltage Protection

(LM3500-16)

Output Overvoltage Protection
(LM3500-21)

I

Vout

V

Bias Current

OUT

ON Threshold 15 15.5 16

OFF Threshold 14 14.6 15

ON Threshold 20 20.5 21

OFF Threshold 19 19.5 20

V

= 15V, SHDN = V

OUT

(LM3500-16)

V

Bias Current

OUT

V

= 20V, SHDN = V

OUT

(LM3500-21)

I

VL

PMOS Switch Leakage

V

= 15V, VSW = 0V

OUT

Current (LM3500-16)

PMOS Switch Leakage

V

= 20V, VSW = 0V

OUT

Current (LM3500-21)

SHDN
Threshold

SHDN Low 0.65 0.3

SHDN High 1.1 0.65

Min

(Note 7)

IN

IN

Typ

(Note 8)

260 400

300 460

0.01 3

0.01 3

Max

(Note 7)

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

Range (TJ = −40°C to +125°C). Unless otherwise specified VIN =2.7V and specification apply to both LM3500-16 and LM3500-21.

Symbol Parameter Conditions

I

Q

Quiescent Current, Device Not
Switching

Quiescent Current, Device
Switching

FB > 0.54V

FB = 0V

Min

(Note 7)

Typ

(Note 8)

0.95 1.2

1.8 2.5

Max

(Note 7)

Shutdown SHDN = 0V 0.1 2 µA

V

ΔV

I

CL

I

B

V

R

D

FB

FB

IN

DSON

Limit

Feedback Voltage VIN = 2.7V to 7V 0.47 0.5 0.53

Feedback Voltage Line
Regulation

Switch Current Limit
(LM3500-16)

Switch Current Limit
(LM3500-21)

FB Pin Bias Current FB = 0.5V (Note 9)

VIN = 2.7V to 7V

VIN = 3.0V, Duty Cycle = 70%

VIN = 3.0V, Duty Cycle = 63%

0.1 0.4 %/V

400

670

45 200 nA

Input Voltage Range 2.7 7.0 V

NMOS Switch R

PMOS Switch R

DSON

DSON

VIN = 2.7V, ISW = 300mA

V

= 6V, ISW = 300mA

OUT

0.43

1.1 2.3

Duty Cycle Limit (LM3500-16) FB = 0V 87

Duty Cycle Limit (LM3500-21) FB = 0V 94

F

SW

I

SD

Switching Frequency

0.8 1.0 1.2 MHz

SHDN Pin Current (Note 10) SHDN = 5.5V 18 30

SHDN = GND 0.1

I

L

Switch Leakage Current

VSW = 15V 0.01 0.5 µA

(LM3500-16)

Switch Leakage Current

VSW = 20V 0.01 2.0

(LM3500-21)

UVP Input Undervoltage Lockout ON Threshold 2.4 2.5 2.6

OFF Threshold 2.3 2.4 2.5

OVP Output Overvoltage Protection

(LM3500-16)

Output Overvoltage Protection
(LM3500-21)

ON Threshold 15 15.5 16

OFF Threshold 14 14.6 15

ON Threshold 20 20.5 21

OFF Threshold 19 19.5 20

Units

V

µA

µA

V

Units

mA

V

mA

Ω

%

µASHDN = 2.7V 9 16

V

V

www.national.com 4

LM3500

Symbol Parameter Conditions

I

Vout

V

Bias Current

OUT

V

= 15V, SHDN = V

OUT

IN

Min

(Note 7)

(LM3500-16)

V

Bias Current

OUT

V

= 20V, SHDN = V

OUT

IN

(LM3500-21)

I

VL

PMOS Switch Leakage

V

= 15V, VSW = 0V

OUT

Current (LM3500-16)

PMOS Switch Leakage

V

= 20V, VSW = 0V

OUT

Current (LM3500-21)

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 VIN < V

Note 3: For more detailed soldering information and specifications, please refer to National Semiconductor Application Note 1112: Micro SMD Wafer Level Chip

Scale Package (AN-1112), available at www.national.com.

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: In applications where high power dissipation and/or poor package thermal resistance is present, the maximum ambient temperature may have to be
derated. Maximum ambient temperature (T
dissipation of the device in the application (P
following equation: T

Note 6: Junction-to-ambient thermal resistance (θJA) is highly application and board-layout dependent. The 75ºC/W figure provided was measured on a 4-layer
test board conforming to JEDEC standards. In applications where high maximum power dissipation exists, special care must be paid to thermal dissipation issues
when designing the board layout.

Note 7: 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 8: Typical numbers are at 25°C and represent the most likely norm.

Note 9: Feedback current flows out of the pin.

Note 10: Current flows into the pin.

SHDN Low 0.65 0.3

SHDN High 1.1 0.65

A-MAX

= T

J-MAX-OP

. If VIN > V

OUT

A-MAX

D-MAX

– (θJA × P

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

OUT

) is dependent on the maximum operating junction temperature (T

), and the junction-to ambient thermal resistance of the part/package in the application (θJA), as given by the

).

D-MAX

Typ

(Note 8)

Max

(Note 7)

260 400

300 460

0.01 3

0.01 3

or VSW pins.

OUT

= 125ºC), the maximum power

J-MAX-OP

Units

µA

µA

V

Typical Performance Characteristics

Switching Quiescent Current vs V

IN

20065755

Non-Switching Quiescent Current vs V

20065756

IN

5 www.national.com

LM3500

2 LED Efficiency vs LED Current

L = Coilcraft DT1608C-223,

Efficiency = 100*(PIN/(2V

LED*ILED

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*(PIN/(3V

LED*ILED

4 LED Efficiency vs LED Current

L = Coilcraft DT1608C-223,

Efficiency = 100*(PIN/(4V

LED*ILED

20065757

))

20065758

))

3 LED Efficiency vs LED Current

L = TDK VLP4612T-220MR34,

Efficiency = 100*(PIN/(3V

LED*ILED

4 LED Efficiency vs LED Current

L = TDK VLP4612T-220MR34,

Efficiency = 100*(PIN/(4V

LED*ILED

20065779

))

20065780

))

20065759

www.national.com 6

20065781