National Semiconductor LM3407 Technical data

January 18, 2008

LM3407 350 mA, Constant Current Output Floating Buck Switching Converter for High Power LEDs

LM3407 350 mA, Constant Current Output Floating Buck Switching Converter for High Power

LEDs

General Description

The LM3407 is a constant current output floating buck switching converter designed to provide constant current to high power LEDs. The device is ideal for automotive, industrial and general lighting applications. The LM3407 has an integrated power N-MOSFET that makes the application solution compact and simple to implement. An external 1% thick-film resistor allows the converter output voltage to adjust as needed to deliver constant current within 10% accuracy to a serially connected LED string of varying number and type. Converter switching frequency is adjustable from 300 kHz to 1 MHz. The LM3407 features a dimming input to enable LED brightness control by Pulse Width Modulation (PWM). Additionally, a separate enable pin allows for low power shutdown. An exposed pad eMSOP-8 package provides excellent heat dissipation and thermal performance. Input UVLO and output open-circuit protection ensure a robust LED driver solution.

Typical Application

Features

Input operating range 4.5V to 30V

■

Output voltage range: 0.1VIN to 0.9V

■

Accurate constant current output

■

Cycle-by-Cycle current limit

■

Independent device enable (CMOS compatible) and PWM

■

dimming control Converter switching frequency adjustable from 300 kHz to

■

1 MHz No external control loop compensation required

■

Supports ceramic and low ESR output capacitors

■

Input Under Voltage Lock Out (UVLO)

■

Thermal shutdown protection

■

eMSOP-8 Package

■

Applications

LED Driver

■

Constant Current Source

■

Automotive Lighting

■

General Illumination

■

Industrial Lighting

■

30046635

Connection Diagram

LM3407

8-Lead Plastic eMSOP-8 Package

Top View

Mini SOIC Exp Pad (MUY08A)

30046602

Ordering Information

Order Number Package Type NSC Package Drawing Supplied As

LM3407MY eMSOP-8 MUY08A 1000 Units on Tape and Reel

LM3407MYX 3500 Units on Tape and Reel

Pin Descriptions

Pin(s) Name Description Application Information

1 ISNS LED Current Sense pin Connect resistor R

sensing resistor should be placed close to this pin.

2 DIM PWM Dimming Input pin Applying logic level PWM signal to this pin controls the average brightness of the

LED string.

3 EN Device Enable pin Applying logic high to this pin or leaving this pin open enables the switcher. When

this pin is pulled low, the switcher is disabled and will enter low power shutdown mode.

4 FS Switching Frequency

Setting pin

5 VIN Input Voltage pin The input voltage should be in the range of 4.5V to 30V.

6 VCC Internal Regulator

Output pin

7 GND Device Ground pin This pin should be connected to the system ground.

8 LX Drain of N-MOSFET

Switch

EP GND Thermal Pad The bottom pad should be connected to ground. For good thermal performance,

Connect resistor RFS from this pin to ground to set the switching frequency.

This output pin should be bypassed by a ceramic capacitor with a minimum value of 1µF. High quality X5R or X7R ceramic capacitor is recommended.

Connect this pin to the output inductor and anode of the Schottky diode.

place 4 to 6 thermal vias from EP to bottom layer PCB ground plane.

from this pin to ground for LED current sensing. The current

ISNS

www.national.com 2

LM3407

Absolute Maximum Ratings (Note 1)

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

VIN to GND -0.3V to 36V VIN to GND (Transient) 42V (500 ms) LX to GND -0.3V to 36V LX to GND (Transient) -3V (2 ns), 42V (500 ms) ISNS, FS, DIM, EN to GND -0.3V to 7V ESD Rating Human Body Model (Note 2) 2kV

Electrical Characteristics V

= 12V unless otherwise indicated. Typical and limits appearing in plain type apply

Junction Temperature 150°C Storage Temperature −65°C to + 125°C Soldering Information Lead Temperature (Soldering,

10sec) Infrared or Convection (20sec) 235°C

Operating Ratings

Junction Temperature Range −40°C to + 125°C

Thermal Resistance (θJA) (Note 3)

4.5V to 30V

50°C/W

for TA = TJ = 25°C (Note 4). Limits appearing in boldface type apply over full Operating Temperature Range. Datasheet min/max specification limits are guaranteed by design, test, or statistical analysis.

Symbol Parameter Conditions Min Typ Max Units

SYSTEM PARAMETERS

SHUT

UVLO

UVLO-HYS

EN_H

EN_L

DIM_H

DIM_L

ON-MIN

SD-HYS

Operating Input Current

Quiescent Input current

4.5V ≤ VIN ≤ 30V

VEN = 5V, V

PWM

4.5V ≤ VIN ≤ 30V

VEN = 5V, V

PWM

= 5V, LX = open

= 0V

0.58 0.78 0.98 mA

0.20 0.27 0.39 mA

Shutdown Input Current VEN = 0V 36 48 60 µA

Input Under Voltage Lock-out Threshold VIN Rising 3.6 4.5 V

UVLO Hysteresis VIN Falling 200 mV

EN pin HIGH Threshold VEN Rising 1.9 2.4 V

EN pin LOW Threshold VEN Falling 1.3 1.75 V

DIM pin HIGH Threshold V

DIM pin LOW Threshold V

Switching Frequency

Rising 1.9 2.4 V

DIM

Falling 1.3 1.75 V

DIM

RT = 80 kΩ

RT = 40 kΩ

500 kHz

1000

Minimum On-time 200 ns

Thermal Shutdown Threshold 165 °C

Thermal Shutdown Hysteresis 25 °C

INTERNAL VOLTAGE REGULATOR

VCC Regulator Output Voltage (Note 5) VIN = 12V 4.5 V

N-MOSFET DRIVER

DS(ON)

Main Switch ON Resistance I

= 80mA 0.77 1.45

sink

CONTROL LOOP

Error Amp Open Loop Gain 60 dB

260°C

Ω

Note 1: Absolute Maximum Ratings are limits beyond which damage to the device may occur. Operating Ratings are conditions under which operation of the device is intended to be functional. For guaranteed specifications and test conditions, see the Electrical Characteristics.

Note 2: The human body model is a 100pF capacitor discharged through a 1.5kΩ resistor into each pin.

Note 3: θJA of 50°C/W with thermal pad, EP soldered to a minimum of 2 square inches of 1 oz. Copper on the top or bottom PCB layer.

Note 4: Typical specification represent the most likely parametric norm at 25°C operation.

Note 5: VCC provides self bias for the internal gate drive and control circuits. Device thermal limitations limit external loading to the pin.

3 www.national.com

Typical Performance Characteristics Unless otherwise specified, all curves shown are taken in typical

application at VIN = 12V, TA = 25°C, and I

LM3407

Output Current vs Input Voltage

(TA = -40°C)

= 350 mA (driving two power LEDs).

LED

Output Current vs Input Voltage

(TA = 25°C)

Output Current vs Input Voltage

(TA = 125°C)

Efficiency vs Input Voltage

(TA = 25°C)

30046603

30046633

30046632

Efficiency vs Input Voltage

(TA = 40°C)

30046604

Efficiency vs Input Voltage

(TA = 125°C)

30046605

www.national.com 4

30046606

LM3407

Switch On Time vs Input Voltage

VCC Voltage vs Input Voltage

30046607

Operating Input Current vs Input Voltage

30046608

Output Current vs R

ISNS

Switching Frequency vs R

30046609

30046611

Continuous Mode Operation

(VIN = 12V, L = 33µH, fSW = 1MHz)

30046610

30046612

5 www.national.com

+ 11 hidden pages