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An IMPORTANT NOTICE at the end of this data sheet addresses availability, warranty, changes, use in safety-critical applications,

intellectual property matters and other important disclaimers. PRODUCTION DATA.

LM3407

SNVS553C –JANUARY 2008–REVISED NOVEMBER 2016

LM3407 350-mA, Constant Current Output Floating Buck Switching Converter

for High-Power LEDs

1 Features

1• Input Operating Range 4.5 V to 30 V

• Output Voltage Range: 0.1 VIN to 0.9 VIN

• Accurate Constant Current Output

• 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 Undervoltage Lockout (UVLO)

• Thermal Shutdown Protection

• MSOP-8 PowerPAD Package

2 Applications

• LED Drivers

• Constant Current Sources

• Automotive Lighting

• General Illumination

• Industrial Lighting

3 Description

The LM3407 device 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-

channel 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 MSOP-8 package

provides excellent heat dissipation and thermal

performance. Input UVLO and output open-circuit

protection ensure a robust LED driver solution.

Device Information(1)

PART NUMBER PACKAGE BODY SIZE (NOM)

LM3407 MSOP-PowerPAD (8) 3.00 mm × 3.00 mm

(1) For all available packages, see the orderable addendum at

the end of the data sheet.

Simplified Application Schematic

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Table of Contents

1 Features.................................................................. 1

2 Applications ........................................................... 1

3 Description............................................................. 1

4 Revision History..................................................... 2

5 Pin Configuration and Functions......................... 3

6 Specifications......................................................... 4

6.1 Absolute Maximum Ratings ...................................... 4

6.2 ESD Ratings.............................................................. 4

6.3 Recommended Operating Conditions....................... 4

6.4 Thermal Information.................................................. 4

6.5 Electrical Characteristics........................................... 5

6.6 Typical Characteristics.............................................. 6

7 Detailed Description.............................................. 9

7.1 Overview................................................................... 9

7.2 Functional Block Diagram......................................... 9

7.3 Feature Description................................................. 10

7.4 Device Functional Modes........................................ 13

8 Application and Implementation ........................ 14

8.1 Application Information............................................ 14

8.2 Typical Applications ................................................ 17

9 Power Supply Recommendations...................... 20

10 Layout................................................................... 20

10.1 Layout Guidelines ................................................. 20

10.2 Layout Example .................................................... 20

11 Device and Documentation Support................. 21

11.1 Documentation Support ....................................... 21

11.2 Receiving Notification of Documentation Updates 21

11.3 Community Resources.......................................... 21

11.4 Trademarks........................................................... 21

11.5 Electrostatic Discharge Caution............................ 21

11.6 Glossary................................................................ 21

12 Mechanical, Packaging, and Orderable

Information........................................................... 21

4 Revision History

NOTE: Page numbers for previous revisions may differ from page numbers in the current version.

Changes from Revision B (May 2013) to Revision C Page

• Added ESD Ratings table, Thermal Information table, Feature Description section, Device Functional Modes,

Application and Implementation section, Power Supply Recommendations section, Layout section, Device and

Documentation Support section, and Mechanical, Packaging, and Orderable Information section....................................... 1

• Changed RθJA for DGN package from 50°C/W to 55.6°C/W.................................................................................................. 4

Changes from Revision A (January 2009) to Revision B Page

• Changed layout of National Semiconductor Data Sheet to TI format. ................................................................................ 20

ISNS

DIM

VCC

GND

VINFS

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5 Pin Configuration and Functions

DGN Package

8-Pin MSOP

Top View

Pin Functions

PIN I/O DESCRIPTION

NO. NAME

1 ISNS I Connect resistor RISNS from this pin to ground for LED current sensing. The current sensing

resistor should be placed close to this pin.

2 DIM I PWM Dimming Control Pin. Applying a logic level PWM signal to this pin controls the

intended brightness of the LED string.

3 EN I Applying logic high to this pin or leaving it open enables the switcher. When pulled low the

switcher is disabled and will enter low power shutdown mode.

4 FS I Switching Frequency Setting Pin. Connect resistor RFS from this pin to ground to set the

switching frequency.

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

6 VCC O Internal Regulator Output Pin. This pin should be bypassed to ground by a ceramic capacitor

with a minimum value of 1 µF.

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

8 LX O Drain of N-MOSFET Switch. Connect this pin to the output inductor and anode of the

Schottky diode.

EP EP — Thermal Pad (Power Ground). Used to dissipate heat from the package during operation.

Must be electrically connected to GND external to the package.

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(1) Stresses beyond those listed under Absolute Maximum Ratings may cause permanent damage to the device. These are stress ratings

only, which do not imply functional operation of the device at these or any other conditions beyond those indicated under Recommended

Operating Conditions. Exposure to absolute-maximum-rated conditions for extended periods may affect device reliability.

6 Specifications

6.1 Absolute Maximum Ratings

over operating free-air temperature range (unless otherwise noted)(1)

MIN MAX UNIT

VIN to GND –0.3 36 V

VIN to GND (transient) 42 (500 ms) V

LX to GND –0.3 36 V

LX to GND (transient) –3 (2 ns) 42 (500 ms) V

FS, ISNS, DIM, EN to GND –0.3 7 V

Storage temperature, Tstg –65 125 °C

(1) JEDEC document JEP155 states that 500-V HBM allows safe manufacturing with a standard ESD control process.

(2) JEDEC document JEP157 states that 250-V CDM allows safe manufacturing with a standard ESD control process.

6.2 ESD Ratings VALUE UNIT

V(ESD) Electrostatic discharge Human-body model (HBM), per ANSI/ESDA/JEDEC JS-001(1) ±2000 V

Charged-device model (CDM), per JEDEC specification JESD22-

C101(2) ±750

6.3 Recommended Operating Conditions

over operating free-air temperature range (unless otherwise noted) MIN MAX UNIT

VIN 4.5 30 V

Junction temperature –40 125 °C

(1) For more information about traditional and new thermal metrics, see the Semiconductor and IC Package Thermal Metrics application

report.

6.4 Thermal Information

THERMAL METRIC(1) LM3407

UNITDGN (MSOP)

8 PINS

RθJA Junction-to-ambient thermal resistance 55.6 °C/W

RθJC(top) Junction-to-case (top) thermal resistance 50.7 °C/W

RθJB Junction-to-board thermal resistance 28.8 °C/W

ψJT Junction-to-top characterization parameter 1.6 °C/W

ψJB Junction-to-board characterization parameter 28.6 °C/W

RθJC(bot) Junction-to-case (bottom) thermal resistance 4.9 °C/W

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(1) All limits specified at room temperature (TYP) and at temperature extremes (MIN/MAX). All room temperature limits are 100%

production tested. All limits at temperature extremes are specified through correlation using standard Statistical Quality Control (SQC)

methods. All limits are used to calculate Average Outgoing Quality Level (AOQL).

(2) Typical specification represent the most likely parametric norm at 25°C operation.

(3) VCC provides self bias for the internal gate drive and control circuits. Device thermal limitations limit external loading to the pin.

6.5 Electrical Characteristics

MIN and MAX limits apply for TJ= –40°C to +125°C unless specified otherwise. VIN = 12 V unless otherwise indicated.

PARAMETER TEST CONDITIONS MIN(1) TYP(2) MAX(1) UNIT

SYSTEM PARAMETERS

IIN Operating input current 4.5 V ≤VIN ≤30 V, LX = open,

VPWM = VEN = 5 V 0.58 0.78 0.98 mA

IQQuiescent Input current 4.5 V ≤VIN ≤30 V,

VPWM = 0 V, VEN = 5 V 0.2 0.27 0.39 mA

ISHUT Shutdown input current VEN = 0 V 36 48 60 µA

VUVLO Input undervoltage lockout

threshold VIN Rising 3.6 4.5 V

VUVLO-HYS UVLO hysteresis VIN Falling 200 mV

VEN_H EN Pin HIGH threshold VEN Rising 1.9 2.4 V

VEN_L EN Pin LOW threshold VEN Falling 1.3 1.75 V

VDIM_H DIM Pin HIGH threshold VDIM Rising 1.9 2.4 V

VDIM_L DIM Pin LOW threshold VDIM Falling 1.3 1.75 V

fSW Switching frequency RT= 80 kΩ500 kHz

RT= 40 kΩ1000

tON-MIN Minimum on-time 200 ns

TSD Thermal shutdown threshold 165 °C

TSD-HYS Thermal shutdown hysteresis 25

INTERNAL VOLTAGE REGULATOR

VCC VCC regulator output voltage(3) VIN = 12 V 4.5 V

MAIN SWITCH

RDS(ON) Main switch ON resistance ISINK = 80 mA 0.77 1.45 Ω

CONTROL LOOP

AEA Error amp open loop gain 60 dB

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6.6 Typical Characteristics

All curves taken at VIN = 12 V with configuration in typical application for driving two power LEDs with ILED = 0.35 A shown in

this data sheet and TA= 25°C, unless otherwise specified.

TA= -40°C

Figure 1. Output Current vs Input Voltage

TA= 25°C

Figure 2. Output Current vs Input Voltage

TA= 125°C

Figure 3. Output Current vs Input Voltage

TA= -40°C

Figure 4. Efficiency vs Input Voltage

TA= 25°C

Figure 5. Efficiency vs Input Voltage

TA= 125°C

Figure 6. Efficiency vs Input Voltage

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Typical Characteristics (continued)

All curves taken at VIN = 12 V with configuration in typical application for driving two power LEDs with ILED = 0.35 A shown in

this data sheet and TA= 25°C, unless otherwise specified.

Figure 7. Switch On Time vs Input Voltage Figure 8. Operating Input Current vs Input Voltage

Figure 9. VCC Voltage vs Input Voltage Figure 10. Output Current vs RISNS

Figure 11. Switching Frequency vs RFS

VIN = 12 V L = 33 µH fSW = 1 MHz

Figure 12. Continuous Mode Operation

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Typical Characteristics (continued)

All curves taken at VIN = 12 V with configuration in typical application for driving two power LEDs with ILED = 0.35 A shown in

this data sheet and TA= 25°C, unless otherwise specified.

VIN = 12 V L = 33 µH fSW = 500 kHz

Figure 13. Continuous Mode Operation

VIN = 24 V L = 33 µH fSW = 1 MHz

Figure 14. Continuous Mode Operation

VIN = 24 V L = 33 µH fSW = 500 kHz

Figure 15. Continuous Mode Operation

VIN = 12 V L = 33 µH fSW = 1 MHz

Figure 16. DIM Pin Enable Transient

VIN = 12 V L = 33 µH fSW = 1 MHz

Figure 17. DIM Pin Disable Transient

VIN

198mV +

Clock

Generator

PWM

Comparator

DIM

GND

ISNS

3.6V

UVLO

SWITCH

CONTROL

Reset

Set

Slope Compensation

Waveform shaping and

Average

Current Sense

VCC

regulator VCC

3.6V

VIN

3.6V

DIM

VCC

400 k:

DIM

5 PA

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7 Detailed Description

7.1 Overview

The LM3407 is a high power floating buck LED driver with a wide input voltage range. The device requires no

loop compensation network. The integrated power N-MOSFET enables high-output power with up to 350-mA

output current. The combination of Pulse Width Modulation (PWM), control architecture, and the proprietary

Pulse Level Modulation (PLM) ensures accurate current regulation, good EMI performance, and provides high

flexibility on inductor selection. High-speed dimming control input allows precision and high resolution brightness

control for applications require fine brightness adjustment.

7.2 Functional Block Diagram

VLX

ILX

ID1

VISNS

ILED, IL1

ILED x RISNS = 198 mV

time

ILED = 198 mV / RISNS

tOFF

tON T

T = tON + tOFF

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7.3 Feature Description

7.3.1 Floating Buck Switching Converter

The LM3407 is designed for floating buck configuration. Different from conventional buck converters, a low-side

power N-MOSFET is used. The floating buck configuration simplifies the driver stage design and reduces the die

size of the power MOSFET. Additionally, the connections of the power diode, inductor and output capacitor are

switched to ground with a ground referenced power switch, Q1. The extraction of inductor current information can

be easily realized by a simple current sensing resistor. These benefits combine to provide a high efficiency, low

cost, and reliable solution for LED lighting applications.

The operation of the LM3407 constant current output floating buck converter is explained below. With the internal

switch Q1 turned ON, current flows through the inductor L1 and the LED array. Energy is also stored in the

magnetic field of the inductor during the ON cycle. The current flowing through RISNS during the ON cycle is

monitored by the Average Current Sensing block. The switch will remain ON until the average inductor current

equals 198 mV / RISNS. When the switch is turned OFF, the magnetic field starts to collapse and the polarity of

the inductor voltage reverses. At the same time, the diode is forward biased and current flows through the LED,

releasing the energy stored in the inductor to the output. True average output current is achieved as the

switching cycle continuously repeats and the Average Current Sensing block controls the ON duty cycle. A

constant current output floating buck converter only works in Continuous Conduction Mode (CCM); if the

converter enters Discontinuous Conduction Mode (DCM) operation, the current regulation will deteriorate and the

accuracy of LED current cannot be maintained. The operating waveforms for the typical application circuit are

shown in Figure 18.

Figure 18. Operating Waveforms of a Floating Buck Converter

fSW = tON + tOFF

D = tON + tOFF

tON

and

VRP

ILX

VISNS

VMSL

time

tOFF

tON T

IL1

IOUT

VREF

IOUT = IL1(AVG)

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Feature Description (continued)

7.3.2 Pulse Level Modulation (PLM)

The LM3407 incorporates the innovative Pulse Level Modulation technique. With an external 1% thick film

resistor connected to the ISNS pin, the converter output voltage can adjust automatically as needed to deliver

constant current within 10% accuracy to a serially connected LED string of different number and type. Pulse

Level Modulation is a novel method to provide precise constant current control with high efficiency. It allows the

use of low side current sensing and facilitates true average output current regulation regardless of the input

voltage and inductor value. Pulse Level Modulation can be treated as a process that transforms a trapezoidal

pulse chain into a square pulse chain with an amplitude equal to the center of inductor current ramp. Figure 19

shows the waveform of the converter in steady state. In the figure, IL1 is the inductor current and ILX is the switch

current into the LX pin. VISNS is the voltage drop across the current sensing resistor RISNS. VMSL is the center of

the inductor current ramp and is a reference pulse that is synchronized and has an identical pulse width to VISNS.

Figure 19. LM3407 Switching Waveforms

The switching frequency and duty ratio of the converter equal:

(1)

By comparing the area of VISNS and VRP over the ON period, an error signal is generated. Such a comparison is

functionally equivalent to comparing the middle level of ISNS to VRP during the ON-period of a switching cycle.

The error signal is fed to a PWM comparator circuit to produce the PWM control pulse to drive the internal power

N-MOSFET. Figure 20 shows the implementation of the PWM switching signal. The error signal is fed to a PWM

comparator circuit to produce the PWM control pulse to drive the internal power N-MOSFET. Figure 20 shows

the implementation of the PWM switching signal.

VISNS VMSL

D/fSW

1/fSW

VRP VREF

Error

Amplifier

D/fSW

1/fSW

PWM signal

Generator

D/fSW

1/fSW

VPWM

PWM

sawtooth

To power switch

VISNS1 VMSL

VISNS2

VMSL

VPWM

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Feature Description (continued)

In closed-loop operation, the difference between VMSL and VRP is reflected in the changes of the switching duty

cycle of the power switch. This behavior is independent of the inductance of the inductor and input voltage

because for the same set of IOUT * RISNS, ON time, and switching period, there exists only one VMSL.Figure 21

shows two sets of current sense signals named VISNS1 and VISNS2 that have identical frequencies and duty cycles

but different shapes of trapezoidal waveforms, each generating identical PWM signals.

Figure 20. Pulse-Level Transformation

When VMSL is higher than VREF, the peak value of VRP, the switching duty cycle of the power switch will be

reduced to lower VMSL. When VMSL is lower than the peak value of VRP, the switching duty cycle of the power

switch will be increased to raise VMSL. For example, when IOUT is decreased, VMSL will become lower than VREF.

In order to maintain output current regulation, the switching duty cycle of the power switch will be increased and

eventually push up VMSL until VMSL equals VREF. Because in typical floating buck regulators VMSL is equal to IOUT

× RISNS, true average output current regulation can be achieved by regulating VMSL.Figure 22 shows the

waveforms of VISNS and VRP under closed loop operation.

Figure 21. Implementation of the PWM Switching Signal

VRP

VISNS

VMSL < VREF VMSL = VREF

tON

IOUT * RISNS

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Feature Description (continued)

Figure 22. Waveforms of VISNS and VRP Under Closed-Loop Operation

7.3.3 Internal VCC Regulator

The LM3407 has an internal 4.5 V linear regulator. This regulated voltage is used for powering the internal

circuitry only and any external loading at the VCC pin is not recommended. The supply input (VIN) can be

connected directly to an input voltage up to 30 V. The VCC pin provides voltage regulated at 4.5 V for VIN ≤6 V.

For 4.5 V ≤VIN ≤6 V, VIN pin will be connected to VCC pin directly by an internal bypassing switch. For stability

reason, an external capacitor CVCC with at least 680 nF (1 µF recommended) must be connected to the VCC pin.

7.3.4 Clock Generator

The LM3407 features an integrated clock generator to control the switching frequency of the converter, fSW. An

external resistor RFS, connected to the FS pin and ground, determines the switching frequency. The oscillator

frequency can be set in the range of 300 kHz to 1 MHz. The relationship between the frequency setting

resistance and the oscillator frequency is described in the Application Information Section.

7.3.5 PWM Dimming of LED String

Dimming of LED brightness is achieved by Pulse Width Modulation (PWM) control of the LED current. Pulse

Width Modulation control allows LED brightness to be adjusted while still maintaining accurate LED color

temperature. The LM3407 accepts an external PWM dimming signal at the DIM pin. The signal is buffered before

being applied to the internal switch control block responsible for controlling the ON/OFF of the power switch, Q1.

The DIM pin is internally pulled low by a resistor and no LED current will be available when the DIM pin is

floating or shorted to ground. Functionally, the DIM pin can also be used as an external device disable control.

Device switching will be disabled if the DIM pin is not connected or tied to ground.

7.3.6 Input Under-Voltage Lock-Out (UVLO)

The LM3407 incorporates an input Under-Voltage Lock-Out (UVLO) circuit with hysteresis to keep the device

disabled when the input voltage (VIN) falls below the Lock-Out Low threshold, 3.4 V typical. During the device

power-up, internal circuits are held inactive and the UVLO comparator monitors the voltage level at the VIN pin

continuously. When the VIN pin voltage exceeds the UVLO threshold, 3.6 V typical, the internal circuits are then

enabled and normal operation begins.

7.4 Device Functional Modes

7.4.1 Low-Power Shutdown Mode

The LM3407 comes with a dedicated device enable pin, EN, for low-power shutdown of the device. By putting

the device in shutdown mode, most of the internal circuits will be disabled and the input current will reduced to

below typically 50 µA. The EN pin is internally pulled high by a 5-µA current source. Connecting the EN pin to

ground will force the device to enter low power shutdown mode. To resume normal operation, leave the EN pin

open or drive with a logic high voltage.

RISNS = IOUT

0.198V

fSW = + 40 in kHz

40 Meg

RFS

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8 Application and Implementation

NOTE

Information in the following applications sections is not part of the TI component

specification, and TI does not warrant its accuracy or completeness. TI’s customers are

responsible for determining suitability of components for their purposes. Customers should

validate and test their design implementation to confirm system functionality.

8.1 Application Information

8.1.1 Switching Frequency Selection

The selection of switching frequency is based on the consideration of the conversion efficiency, size of the

passive components, and the total solution cost. In general, increasing the switching frequency allows the use of

smaller external components but decreases the conversion efficiency. Thus, the selection of switching frequency

is a compromise between the system requirements and may vary from design to design. The LM3407 switching

frequency can be set in the range from 300 kHz to 1 MHz by adjusting the value of RFS. The switching frequency

is inversely proportional to the value of RFS. To ensure good operation stability, a resistor with 1% tolerance

between 40 kΩand 96 kΩand with good thermal stability is suggested.

The switching frequency is estimated by Equation 2:

where

• fSW is the oscillator frequency

• RFS is the frequency setting resistance (2)

Equation 2 is only valid for oscillator frequencies in the range of 300 kHz to 1 MHz, so the frequency setting

resistance will be in the range of about 40 kΩto 150 kΩ.

8.1.2 LED Current Setting

The LED current setting is important to the lifetime, reliability, and color temperature of the LED string. The LED

current should be properly selected according to the characteristics of the LED used. Over-driving the LED array

can cause the color temperature to shift and will shorten the lifetime of the LEDs. The output current of the

LM3407 can be set by RISNS, which is calculated from Equation 3:

(3)

To ensure the accuracy of the output current, a resistor with 1% tolerance should be used for RISNS. It is also

important for the designer to ensure that the rated power of the resistor is not exceeded with reasonable margin.

For example, when IOUT is set to 350 mA, the total power dissipation on RISNS in steady state is (0.35 A)2× 0.565

Ω, which equals 69 mW, indicating a resistor of 1/8W power rating is appropriate.

8.1.3 Input and Output Capacitors

The input capacitor supplies instantaneous current to the LM3407 converter when the internal power switch Q1

turns ON. The input capacitor filters the noise and transient voltage from the input power source. Using low ESR

capacitors such as ceramic and tantalum capacitors is recommended. Similar to the selection criteria for the

output capacitor, ceramic capacitors are the best choice for the input to the LM3407 due to their high ripple

current rating, low ESR, and relatively small size compared to other types. A 4.7-µF X7R ceramic capacitor for

the input capacitor is recommended

Lmin = VIN - (n x VF) - 0.198 x x (RISNS x n x VF)

RISNS

1 +

0.197 x VIN x fSW

IL(peak) = RISNS

0.198 + IL(ripple)

IL(ripple) = VIN - (n x VF) - 0.198 x (n x VF)

RISNS

1 +

L x VIN x fSW

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Application Information (continued)

The output capacitor COUT is used to reduce LED current ripple, filter noise, and smooth output voltage. This

capacitor should have low ESR and adequate capacitance. Excessively large output capacitances create long

enable and disable times, which is particularly significant when a high dimming frequency is used. Because the

loading and input conditions differ from design to design, a 2.2-µF X7R ceramic capacitor is a good initial

selection. A DC voltage rating equal to or higher than twice the forward voltage of the LED string is

recommended.

COUT is optional and can be omitted for applications where small brightness variation is acceptable. Omitting

COUT also helps reduce the cost and board size of the converter. With the absence of COUT, the LED forward

current equals the inductor current. To ensure proper operation of the converter, the peak inductor current must

not exceed the rated forward current of the LEDs. Otherwise the LEDs may be damaged.

8.1.4 Selection of Inductor

To achieve accurate constant current output, the LM3407 is required to operate in Continuous Conduction Mode

(CCM) under all operating conditions. In general, the magnitude of the inductor ripple current should be kept as

small as possible. If the PCB size is not limited, higher inductance values result in better accuracy of the output

current. However, to minimize the physical size of the circuit, an inductor with minimum physical outline should

be selected such that the converter always operates in CCM and the peak inductor current does not exceed the

saturation current limit of the inductor. The ripple and peak current of the inductor can be calculated as follows:

Inductor Peak to Peak Ripple Current:

(4)

Peak Inductor Current:

where

• n is the number of LEDs in a string

• VFis the forward voltage of one LED. (5)

The minimum inductance required for the specific application can be calculated by Equation 6:

(6)

For applications with no output capacitor in place, the magnitude of the inductor ripple current should not be

more than 20% of the average inductor current, which is equivalent to the output current, IOUT. However, in some

situations the physical size of the required inductor may be too large and thus not allowed. The output capacitor

can help absorb this current ripple to significantly reduce the ripple component along the LED string. With an

output capacitor COUT in place, the magnitude of the inductor ripple current can be relaxed to 80% of the output

current. Figure 23 illustrates the relationship between IOUT, IL(peak), and IL(ripple).

time

tOFF

tON T

IL1

IOUT IL (ripple)

IL (peak)

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Application Information (continued)

Figure 23. Relationship Between IOUT, IL(peak) and IL(ripple)

Table 1 provides the suggested inductance of the inductor for 500 kHz and 1 MHz switching frequency operation

with COUT = 4.7 µF and IL(ripple) = 0.8 × IOUT

Table 1. Suggested Inductance Value of the Inductor

VIN / V Number of LED

1234567

Inductor selection table for FSW = 500 kHz, COUT = 4.7 µF (1 µF for 1 LED)

5 22 µH

10 22 µH 22 µH

15 22 µH 22 µH 22 µH

20 22 µH 33 µH 22 µH 22 µH 22 µH

25 22 µH 33 µH 33 µH 22 µH 22 µH 22 µH

30 22 µH 47 µH 33 µH 33 µH 33 µH 22 µH 22 µH

Inductor selection table for FSW = 1 MHz, COUT = 4.7 µF (1 µF for 1 LED)

5 22 µH

10 22 µH 22 µH

15 22 µH 22 µH 22 µH

20 22 µH 22 µH 22 µH 22 µH 22 µH

25 22 µH 33 µH 22 µH 22 µH 22 µH 22 µH

30 22 µH 33 µH 33 µH 33 µH 22 µH 22 µH 22 µH

8.1.5 Free-Wheeling Diode

The LM3407 is a non-synchronous floating buck converter that requires an external free-wheeling diode to

provide a path for recirculating current from the inductor to the LED array when the power switch is turned OFF.

Selecting the free-wheeling diode depends on both the output voltage and current. The diode must have a rated

reverse voltage higher than the input voltage of the converter and a peak current rating higher than the expected

maximum inductor current. Using a schottky diode with a low forward voltage drop can reduce power dissipation

and enhance conversion efficiency.

RFS = 40 × 106

fSW - 40 = 40 × 106

1000 - 40 = 41.6k

RISNS = 0.198V

IOUT = 0.198V

0.35A 

LM3407

www.ti.com

SNVS553C –JANUARY 2008–REVISED NOVEMBER 2016

Product Folder Links: LM3407

8.2 Typical Applications

8.2.1 LM3407 Design Example

Figure 24. LM3407 Design Example Schematic

8.2.1.1 Design Requirements

• Input Voltage: VIN = 12 V ±10%

• LED String Voltage: VLED = 6.4 V (2 series white LEDs)

• LED Current: ILED = 350 mA

• Switching Frequency: fSW = 1 MHz

8.2.1.2 Detailed Design Procedure

This design is intended to be a small size, low-cost solution. An output capacitor will not be used to save on size

and cost so a high switching frequency will be used and a higher value inductor than recommended in Table 1

will be used to keep LED current ripple lower.

8.2.1.2.1 Calculate RISNS

For 350 mA LED current calculate the value for RISNS using Equation 7.

(7)

Choose a standard value of RISNS = 0.565 Ω.

8.2.1.2.2 Calculate RFS

Calculate the value of RFS for 1-MHz switching frequency using Equation 8.

(8)

Choose a standard value of RFS = 40.2 kΩ.

8.2.1.2.3 Choose L

Referring to Table 1 the recommended inductor value for 12 V input and 2 LED output is 22 µH.

Choose a higher standard value of L = 33 µH to reduce ripple since an output capacitor will not be used for this

design.

LM3407

SNVS553C –JANUARY 2008–REVISED NOVEMBER 2016

www.ti.com

Product Folder Links: LM3407

Typical Applications (continued)

8.2.1.2.4 Choose CIN and CVCC

Choose the recommended values of CIN = 4.7 µF and CVCC = 1 µF. CIN should be a 16 V or greater ceramic

capacitor and CVCC should be a 10 V or greater ceramic capacitor. Both should use an X5R or X7R dielectric.

8.2.1.3 Application Curve

Figure 25. LED Current and Switch Voltage Waveforms

8.2.2 Typical Application for Driving 6 LEDs

Figure 26 shows a high voltage, 6-W application for driving 6 LEDs. The switching frequency is set at 1 MHz and

the LED current is set at 350 mA.

Figure 26. LM3407 6 LED Example Schematic

LM3407

www.ti.com

SNVS553C –JANUARY 2008–REVISED NOVEMBER 2016

Product Folder Links: LM3407

Typical Applications (continued)

8.2.3 Typical Application for Driving 1 LED

Figure 27 shows a low voltage, 1-W application for driving 1 LED. The switching frequency is set at 1 MHz and

the LED current is set at 350 mA.

Figure 27. LM3407 1 LED Example Schematic

ISNS

DIM

GND

VCC

VIN

THERMAL/POWER VIA

GND

RFS

RISNS

CIN

CVCC

VIN/LED+

LED-

GGND

LM3407

SNVS553C –JANUARY 2008–REVISED NOVEMBER 2016

www.ti.com

Product Folder Links: LM3407

9 Power Supply Recommendations

Use any DC output power supply with a maximum voltage high enough for the application. The power supply

should have a minimum current limit of at least 1 A.

10 Layout

10.1 Layout Guidelines

Because the copper traces of PCBs carry resistance and parasitic inductance, the longer the copper trace, the

higher the resistance and inductance. These factors introduce voltage and current spikes to the switching nodes

and may impair circuit performance. To optimize the performance of the LM3407, the rule of thumb is to keep the

connections between components as short and direct as possible. Because true average current regulation is

achieved by detecting the average switch current, the current setting resistor RISNS must be located as close as

possible to the LM3407 to reduce the parasitic inductance of the copper trace and avoid noise pick-up. The

connections between the LX pin, rectifier D1, inductor L1, and output capacitor COUT should be kept as short as

possible to reduce the voltage spikes at the LX pin. TI recommends that CVCC, the output filter capacitor for the

internal linear regulator of the LM3407, be placed close to the VCC pin. The input filter capacitor CIN should be

located close to L1 and the cathode of D1. If CIN is connected to the VIN pin by a long trace, a 0.1-µF capacitor

should be added close to VIN pin for noise filtering.

CAUTION

In normal operation, heat will be generated inside the LM3407 and may damage the

device if no thermal management is applied. For more details on switching power

supply layout considerations see AN-1149 Layout Guidelines for Switching Power

Supplies (SNVA021).

10.2 Layout Example

Figure 28. Layout Recommendation

LM3407

www.ti.com

SNVS553C –JANUARY 2008–REVISED NOVEMBER 2016

Product Folder Links: LM3407

11 Device and Documentation Support

11.1 Documentation Support

11.1.1 Related Documentation

For related documentation see the following:

AN-1149 Layout Guidelines for Switching Power Supplies (SNVA021).

11.2 Receiving Notification of Documentation Updates

To receive notification of documentation updates, navigate to the device product folder on ti.com. In the upper

right corner, click on Alert me to register and receive a weekly digest of any product information that has

changed. For change details, review the revision history included in any revised document.

11.3 Community Resources

The following links connect to TI community resources. Linked contents are provided "AS IS" by the respective

contributors. They do not constitute TI specifications and do not necessarily reflect TI's views; see TI's Terms of

Use.

TI E2E™ Online Community TI's Engineer-to-Engineer (E2E) Community. Created to foster collaboration

among engineers. At e2e.ti.com, you can ask questions, share knowledge, explore ideas and help

solve problems with fellow engineers.

Design Support TI's Design Support Quickly find helpful E2E forums along with design support tools and

contact information for technical support.

11.4 Trademarks

E2E is a trademark of Texas Instruments.

All other trademarks are the property of their respective owners.

11.5 Electrostatic Discharge Caution

These devices have limited built-in ESD protection. The leads should be shorted together or the device placed in conductive foam

during storage or handling to prevent electrostatic damage to the MOS gates.

11.6 Glossary

SLYZ022 —TI Glossary.

This glossary lists and explains terms, acronyms, and definitions.

12 Mechanical, Packaging, and Orderable Information

The following pages include mechanical, packaging, and orderable information. This information is the most

current data available for the designated devices. This data is subject to change without notice and revision of

this document. For browser-based versions of this data sheet, refer to the left-hand navigation.

PACKAGE OPTION ADDENDUM

www.ti.com 10-Dec-2020

Addendum-Page 1

PACKAGING INFORMATION

Orderable Device Status

(1)

Package Type Package

Drawing Pins Package

Qty Eco Plan

(2)

Lead finish/

Ball material

(6)

MSL Peak Temp

(3)

Op Temp (°C) Device Marking

(4/5)

Samples

LM3407MY/NOPB ACTIVE HVSSOP DGN 8 1000 RoHS & Green SN Level-1-260C-UNLIM -40 to 125 STZB

LM3407MYX/NOPB ACTIVE HVSSOP DGN 8 3500 RoHS & Green SN Level-1-260C-UNLIM -40 to 125 STZB

(1) The marketing status values are defined as follows:

ACTIVE: Product device recommended for new designs.

LIFEBUY: TI has announced that the device will be discontinued, and a lifetime-buy period is in effect.

NRND: Not recommended for new designs. Device is in production to support existing customers, but TI does not recommend using this part in a new design.

PREVIEW: Device has been announced but is not in production. Samples may or may not be available.

OBSOLETE: TI has discontinued the production of the device.

(2) RoHS: TI defines "RoHS" to mean semiconductor products that are compliant with the current EU RoHS requirements for all 10 RoHS substances, including the requirement that RoHS substance

do not exceed 0.1% by weight in homogeneous materials. Where designed to be soldered at high temperatures, "RoHS" products are suitable for use in specified lead-free processes. TI may

reference these types of products as "Pb-Free".

RoHS Exempt: TI defines "RoHS Exempt" to mean products that contain lead but are compliant with EU RoHS pursuant to a specific EU RoHS exemption.

Green: TI defines "Green" to mean the content of Chlorine (Cl) and Bromine (Br) based flame retardants meet JS709B low halogen requirements of <=1000ppm threshold. Antimony trioxide based

flame retardants must also meet the <=1000ppm threshold requirement.

(3) MSL, Peak Temp. - The Moisture Sensitivity Level rating according to the JEDEC industry standard classifications, and peak solder temperature.

(4) There may be additional marking, which relates to the logo, the lot trace code information, or the environmental category on the device.

(5) Multiple Device Markings will be inside parentheses. Only one Device Marking contained in parentheses and separated by a "~" will appear on a device. If a line is indented then it is a continuation

of the previous line and the two combined represent the entire Device Marking for that device.

(6) Lead finish/Ball material - Orderable Devices may have multiple material finish options. Finish options are separated by a vertical ruled line. Lead finish/Ball material values may wrap to two

lines if the finish value exceeds the maximum column width.

Important Information and Disclaimer:The information provided on this page represents TI's knowledge and belief as of the date that it is provided. TI bases its knowledge and belief on information

provided by third parties, and makes no representation or warranty as to the accuracy of such information. Efforts are underway to better integrate information from third parties. TI has taken and

continues to take reasonable steps to provide representative and accurate information but may not have conducted destructive testing or chemical analysis on incoming materials and chemicals.

TI and TI suppliers consider certain information to be proprietary, and thus CAS numbers and other limited information may not be available for release.

In no event shall TI's liability arising out of such information exceed the total purchase price of the TI part(s) at issue in this document sold by TI to Customer on an annual basis.

PACKAGE OPTION ADDENDUM

www.ti.com 10-Dec-2020

Addendum-Page 2

TAPE AND REEL INFORMATION

*All dimensions are nominal

Device Package

Type Package

Drawing Pins SPQ Reel

Diameter

(mm)

Reel

Width

W1 (mm)

(mm) B0

(mm) K0

(mm) P1

(mm) W

(mm) Pin1

Quadrant

LM3407MY/NOPB HVSSOP DGN 8 1000 178.0 12.4 5.3 3.4 1.4 8.0 12.0 Q1

LM3407MYX/NOPB HVSSOP DGN 8 3500 330.0 12.4 5.3 3.4 1.4 8.0 12.0 Q1

PACKAGE MATERIALS INFORMATION

www.ti.com 6-Sep-2019

Pack Materials-Page 1

*All dimensions are nominal

Device Package Type Package Drawing Pins SPQ Length (mm) Width (mm) Height (mm)

LM3407MY/NOPB HVSSOP DGN 8 1000 210.0 185.0 35.0

LM3407MYX/NOPB HVSSOP DGN 8 3500 367.0 367.0 35.0

PACKAGE MATERIALS INFORMATION

www.ti.com 6-Sep-2019

Pack Materials-Page 2

www.ti.com

PACKAGE OUTLINE

6X 0.65

1.95

8X 0.38

0.25

5.05

4.75 TYP

SEATING

PLANE

0.15

0.05

0.25

GAGE PLANE

0 -8

1.1 MAX

0.23

0.13

1.88

1.58

2.0

1.7

B3.1

2.9

NOTE 4

3.1

2.9

NOTE 3

0.7

0.4

PowerPAD VSSOP - 1.1 mm max heightDGN0008A

SMALL OUTLINE PACKAGE

4218836/A 11/2019

0.13 C A B

PIN 1 INDEX AREA

SEE DETAIL A

0.1 C

NOTES:

1. All linear dimensions are in millimeters. Any dimensions in parenthesis are for reference only. Dimensioning and tolerancing

per ASME Y14.5M.

2. This drawing is subject to change without notice.

3. This dimension does not include mold flash, protrusions, or gate burrs. Mold flash, protrusions, or gate burrs shall not

exceed 0.15 mm per side.

4. This dimension does not include interlead flash. Interlead flash shall not exceed 0.25 mm per side.

5. Reference JEDEC registration MO-187.

PowerPAD is a trademark of Texas Instruments.

A 20

DETAIL A

TYPICAL

SCALE 4.000

EXPOSED THERMAL PAD

www.ti.com

EXAMPLE BOARD LAYOUT

0.05 MAX

ALL AROUND 0.05 MIN

ALL AROUND

8X (1.4)

8X (0.45)

6X (0.65)

(4.4)

(R0.05) TYP

(2)

NOTE 9

(3)

NOTE 9

(1.22)

(0.55)

( 0.2) TYP

VIA

(1.88)

(2)

PowerPAD VSSOP - 1.1 mm max heightDGN0008A

SMALL OUTLINE PACKAGE

4218836/A 11/2019

NOTES: (continued)

6. Publication IPC-7351 may have alternate designs.

7. Solder mask tolerances between and around signal pads can vary based on board fabrication site.

8. Vias are optional depending on application, refer to device data sheet. If any vias are implemented, refer to their locations shown

on this view. It is recommended that vias under paste be filled, plugged or tented.

9. Size of metal pad may vary due to creepage requirement.

LAND PATTERN EXAMPLE

EXPOSED METAL SHOWN

SCALE: 15X

SYMM

SOLDER MASK

DEFINED PAD

METAL COVERED

BY SOLDER MASK

SEE DETAILS

15.000

METAL

SOLDER MASK

OPENING METAL UNDER

SOLDER MASK SOLDER MASK

OPENING

EXPOSED METAL

SOLDER MASK DETAILS

NON-SOLDER MASK

DEFINED

(PREFERRED)

SOLDER MASK

DEFINED

www.ti.com

EXAMPLE STENCIL DESIGN

8X (1.4)

8X (0.45)

6X (0.65)

(4.4)

(R0.05) TYP

(1.88)

BASED ON

0.125 THICK

STENCIL

(2)

BASED ON

0.125 THICK

STENCIL

PowerPAD VSSOP - 1.1 mm max heightDGN0008A

SMALL OUTLINE PACKAGE

4218836/A 11/2019

1.59 X 1.690.175 1.72 X 1.830.15 1.88 X 2.00 (SHOWN)0.125 2.10 X 2.240.1

SOLDER STENCIL

OPENING

STENCIL

THICKNESS

NOTES: (continued)

10. Laser cutting apertures with trapezoidal walls and rounded corners may offer better paste release. IPC-7525 may have alternate

design recommendations.

11. Board assembly site may have different recommendations for stencil design.

SOLDER PASTE EXAMPLE

EXPOSED PAD 9:

100% PRINTED SOLDER COVERAGE BY AREA

SCALE: 15X

SYMM

METAL COVERED

BY SOLDER MASK SEE TABLE FOR

DIFFERENT OPENINGS

FOR OTHER STENCIL

THICKNESSES

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