LM3639AYFQR_技术文档

LM3639A

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SNVS964 –MARCH 2013

LM3639A Single Chip 40V Backlight + 1.5A Flash LED Driver

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1

FEATURES

DESCRIPTION

The LM3639A is a single-chip white LED Camera

Flash Driver + LCD Display Backlight Driver. The low-

2

•

Single Chip White LED Flash and Backlight

Driver

voltage, high-current flash LED driver is

a

•

1.5A Flash LED Current

synchronous boost which provides the power for a

single flash LED at up to 1.5A or dual LEDs at up to

750 mA each. The high-voltage backlight driver is a

dual-output asynchronous boost which powers dual

LED strings at up to 40V and 30 mA per string. An

adaptive regulation method in both boost converters

regulates the headroom voltage across the respective

source/sink to ensure the LED current remains in

Dual String Backlight Control (40V Max V_OUT

)

128 Level Exponential and Linear Brightness

Control

•

PWM Input for CABC

Programmable Over-Voltage Protection

(Backlight)

regulation

while

maximizing

efficiency.

The

•

Programmable Current Limit (Flash)

Programmable Switching Frequency

LM3639A's flash driver is a 2MHz or 4MHz fixed-

frequency synchronous boost converter plus 1.5A

constant current driver for a high-current white LED.

The high-side current source allows for grounded

cathode LED operation providing Flash current up to

1.5A. An adaptive regulation method ensures the

current source remains in regulation and maximizes

efficiency.

The device is controlled by an I²C-compatible

interface. Features for the flash LED driver include a

hardware flash enable (STROBE) allowing a logic

input to trigger the flash pulse, and a TX input for

synchronization to RF power amplifier events or other

high current conditions. Features for the LCD

backlight driver include a PWM input for content

adjustable backlight control, 128 exponential or linear

Optimized Flash Current During Low-Battery

Conditions

APPLICATIONS

•

White LED Backlit Display Power

White LED Camera Flash Power

VOUTB

up to 40V

L(B)

Schottky

L(F)

COUTB

SWF SWB

OVP

OUTF

OR

VIN

2.5V - 5.5V

CIN

COUTF

brightness

levels,

programmable

over-voltage

EN

protection, and selectable switching frequency (500

kHz or 1 MHz).

SCL

SDA

STROBE

BLED1

BLED2

The device is available in a tiny 1.790 mm x 2.165

mm x 0.6 mm 20-bump, 0.4 mm pitch DSBGA

package and operates over the −40°C to +85°C

temperature range.

TX

FLED1

FLED2

PWM

FLED2

FLED1

GND

1

Please be aware that an important notice concerning availability, standard warranty, and use in critical applications of

Texas Instruments semiconductor products and disclaimers thereto appears at the end of this data sheet.

2

All trademarks are the property of their respective owners.

PRODUCTION DATA information is current as of publication date.

Products conform to specifications per the terms of the Texas

Instruments standard warranty. Production processing does not

necessarily include testing of all parameters.

LM3639A

SNVS964 –MARCH 2013

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This integrated circuit can be damaged by ESD. Texas Instruments recommends that all integrated circuits be handled with

appropriate precautions. Failure to observe proper handling and installation procedures can cause damage.

ESD damage can range from subtle performance degradation to complete device failure. Precision integrated circuits may be more

susceptible to damage because very small parametric changes could cause the device not to meet its published specifications.

Connection Diagram

4

3

2

1

4

3

2

1

A

B

C

D

E

D

C

B

A

Top View

Bottom View

Figure 1. 20-Bump, 0.4 mm Pitch DSBGA Package

YFQ0020HGA

PIN DESCRIPTIONS

TERMINAL

I/O

DESCRIPTION

NAME

FLED1

NO.

A1

Output

High Side Current Source Output for Flash LED1.

High Side Current Source Output for Flash LED2.

FLED2

B1

Flash LED Boost Output. Connect a 10 µF ceramic capacitor between this

pin GND.

OUTF (x2)

SWF (x2)

A2/B2

A3/B3

Output

Drain Connection for Internal NMOS and Synchronous PMOS Switches.

Connect the Flash LED Boost Inductor to SWF.

GND (x3)

TX

A4/B4/E3

C2

Ground

Power Amplifier Synchronization Input. The TX pin has a 300 kΩ pull-down

resistor connected to GND.

Input

Active High Hardware Flash Enable. Drive STROBE high to turn on Flash

pulse. STROBE overrides TORCH. The STROBE pin has a 300 kΩ pull-

down resistor connected to GND.

STROBE

VIN

C3

C4

Input Voltage Connection. Connect IN to the input supply, and bypass to

GND with a 10 µF or larger ceramic capacitor.

SDA

SCL

EN

D3

D2

C1

Input

Serial Data Input/Output.

Serial Clock Input.

Enable Pin. High = Standby, Low = Shutdown/Reset.

Drain Connection for internal NFET. Connect SWB to the junction of the

backlight boost inductor and the Schottky diode anode.

SWB

E4

D4

D1

E1

E2

Input

PWM Brightness Control Input for backlight current control. The PWM pin

has a 300 kΩ pull-down resistor connected to GND.

PWM

BLED1

BLED2

OVP

Input Terminal to Backlight LED String Current Sink #1 (40V max). The boost

converter regulates the minimum of BLED1 and BLED2 to 400 mV.

Input Terminal to Backlight LED String Current Sink #2 (40V max). The boost

converter regulates the minimum of BLED1 and BLED2 to 400 mV.

Over-Voltage Sense Input for Backlight Boost. Connect to the positive

terminal of (COUTB).

2

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SNVS964 –MARCH 2013

(1)

ABSOLUTE MAXIMUM RATINGS

VIN

(2) (3)

−0.3V to 6V

−0.3V to the lesser of (V_IN+0.3V) w/ 6V

(2)

SWF, OUTF, FLED1, FLED2, EN, PWM, SCL, SDA, TX, STROBE

max

(2)

SWB, OVP, BLED1, BLED2

−0.3V to +45V

Storage Temperature Range

−65°C to +150°C

(1) Absolute Maximum Ratings indicate limits beyond which damage to the device may occur. Operating Ratings are conditions under

which operation of the device is ensured. Operating Ratings do not imply ensured performance limits. For ensured performance limits

and associated test conditions, see the Electrical Characteristics table.

(2) All voltages are with respect to the potential at the GND pin.

(3) V_INcan be below −0.3V if the current out of the pin is limited to 500 µA.

(1) (2)

OPERATING RATINGS

V_IN

2.5V to 5.5V

−40°C to +125°C

−40°C to +85°C

Junction Temperature (T_J)

Ambient Temperature (T_A)

(3)

(1) Absolute Maximum Ratings indicate limits beyond which damage to the device may occur. Operating Ratings are conditions under

which operation of the device is ensured. Operating Ratings do not imply ensured performance limits. For ensured performance limits

and associated test conditions, see the Electrical Characteristics table.

(2) All voltages are with respect to the potential at the GND pin.

(3) 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_A-MAX) is dependent on the maximum operating junction temperature (T_J-MAX-OP

=

+125°C), the maximum power dissipation of the device in the application (P_D-MAX), and the junction-to-ambient thermal resistance of the

part/package in the application (θ_JA), as given by the following equation: T_A-MAX= T_J-MAX-OP– (θ_JA× P_D-MAX).

THERMAL PROPERTIES

Thermal Junction-to-Ambient Resistance (θ_JA

(1)

)

48.8°C/W

(1) Junction-to-ambient thermal resistance (θ_JA) is taken from a thermal modeling result, performed under the conditions and guidelines set

forth in the JEDEC standard JESD51-7. The test board is a 4-layer FR-4 board measuring 102mm x 76mm x 1.6mm with a 2 x 1 array

of thermal vias. The ground plane on the board is 50mm x 50mm. Thickness of copper layers are 36μm/18μm/18μm/36μm

(1.5oz/1oz/1oz/1.5oz). Ambient temperature in simulation is 22°C in still air. Power dissipation is 1W. In applications where high

maximum power dissipation exists special care must be paid to thermal dissipation issues.

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(1) (2)

ELECTRICAL CHARACTERISTICS

Limits in standard typeface are for T_A= +25°C. Limits in boldface type apply over the full operating ambient temperature

range (−40°C ≤ T_A≤ +85°C). Unless otherwise specified, V_IN= 3.6V.

Symbol

V_IN

Parameter

Input Voltage Range

Shutdown Supply Current

Test Conditions

Min

Typ

3.6

1

Max

5.5

Unit

2.5

V

I_SHDN

Device Shutdown, EN = GND

3.5

Device Disabled via I²C

EN = VIN

µA

I_SB

Standby Supply Current

1

4

Low Voltage Boost Specifications (Flash Driver)

750 mA Flash

Current Setting

−7%

1.5

+7%

A

28.125 mA Torch

Current Setting,

per current

I_FLED1+ I_FLED2

Current Source Accuracy

2.7V ≤ V_IN≤ 5.5V

−10%

56.25

+10%

mA

source

For 750 mA Flash Current Setting

For 28.125 mA Torch Current Setting

ON Threshold

315

180

5

V_HR1, V_HR2

Regulated Headroom Voltage

mV

V

4.87

4.71

5.10

4.98

Output Over-Voltage

Protection Trip Point

V_OVP

OFF Threshold

4.88

85

R_PMOS

R_NMOS

PMOS Switch On-Resistance I_PMOS= 1A

NMOS Switch On-Resistance I_NMOS= 1A

mΩ

75

−12%

1.7

1.9

2.5

3.1

12%

I_CL

Switch Current Limit

V_IN= 3.6V

A

Input Voltage Monitor

Threshold

V_IVM

f_SW

IQ

V_INFalling

−4%

2.5

4.00

0.6

4%

4.36

2

V

Switching Frequency

2.5V ≤ V_IN≤ 5.5V

3.64

MHz

mA

Device Not Switching

Pass Mode, Backlight Disabled

Quiescent Supply Current

Flash to Torch LED Current

Settling Time

TX low to High, ILED1,2 = 750 mA to

23.44 mA

t_TX

4

µs

High Voltage Boost Specification (Backlight Driver)

Output Current Regulation

(BLED1 or BLED2)

2.7V ≤ V_IN≤ 5.5V, Full Scale Current =

19 mA, Brightness Register = 0xFF

I_BLED1, I_BLED2

I_{MATCH_HV}

V_{REG_CS}

−7%

19

1

7%

mA

%

BLED1 to BLED2 Current

Matching⁽³⁾

2.7V ≤ V_IN≤ 5.5V, Full Scale Current =

19 mA, Brightness Register = 0xFF

2.25

Regulated Current Sink

Headroom Voltage

I_LED= 19mA

400

130

mV

Current Sink Minimum

Headroom Voltage

V_{HR_MIN}

I_LED= 95% of I_LED= 19 mA

R_DSON

NMOS Switch On Resistance I_SW= 500 mA

230

1

mΩ

I_{CL_BOOST}

NMOS Switch Current Limit

V_IN= 3.6V

−10%

10%

41.4

A

ON Threshold, 2.7V ≤ VIN ≤ 5.5V,

OVP select bits = 11

38.4

40.0

1

Output Over-Voltage

Protection

V_OVP

V

Hysteresis

2.5V ≤ VIN ≤ 5.5V,

Boost Frequency

Select Bit = '0'

f_SW

Switching Frequency

Maximum Duty Cycle

465

500

94

535

kHz

%

D_MAX

(1) All voltages are with respect to the potential at the GND pin.

(2) JESD ESD tests are applied at the ASIC level. 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.

(3) Matching (%)= 100 × (|(ILED1 - ILED2 )| / (ILED1 + ILED2))

4

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ELECTRICAL CHARACTERISTICS ^{(1) (2)}(continued)

Limits in standard typeface are for T_A= +25°C. Limits in boldface type apply over the full operating ambient temperature

range (−40°C ≤ T_A≤ +85°C). Unless otherwise specified, V_IN= 3.6V.

Symbol

Parameter

Test Conditions

Min

Typ

Max

Unit

Logic Input Voltage Specifications (EN, STROBE, TORCH, TX, PWM)

V_IL

V_IH

Input Logic Low

Input Logic High

2.5V ≤ VIN ≤ 5.5V

0

0.4

V

1.2

V_IN

Logic Input Voltage Specifications (SCL, SDA)

V_OL

V_IL

Output Logic Low (SDA only)

Input Logic Low

I_LOAD= 3 mA

400

0.4

V_IN

mV

V

2.5V ≤ VIN ≤ 5.5V

2.5V ≤ VIN ≤ 4.2V

0

V_IH

Input Logic High

1.2

I²C-Compatible Timing Specifications (SCL, SDA)

1/t1

SCL (Clock Frequency)

kHz

ns

Data In Setup Time to SCL

High

t2

100

0

Data Out Stable After SCL

Low

t3

t4

t5

SDA Low Setup Time to SCL

Low (Start)

100

SDA High Hold Time After

SCL High (Stop)

SDA

Figure 2. I²C Timing Diagram

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TYPICAL PERFORMANCE CHARACTERISTICS

Unless otherwise specified: T_A= 25°C; V_IN= 3.6V; V_EN= VIN; CIN= 10 μF, COUTF= 10 μF, COUTB = 1 μF (50V 0805 case

size); LF = 1 μH; LB = 22 μH.

0.8

0.79

0.78

0.77

0.76

0.75

0.74

0.73

0.72

0.71

0.7

0.8

0.79

0.78

0.77

0.76

0.75

0.74

0.73

0.72

0.71

0.7

D1, +25°C

D2, +25°C

D1, +85°C

D2, +85°C

D1, -40°C

D2, -40°C

D1, +25°C

D2, +25°C

D1, +85°C

D2, +85°C

D1, -40°C

D2, -40°C

f_SW= 2MHz

f_SW= 4MHz

2.7

3

3.3

3.6

3.9

4.2

4.5

4.8

2.7

3

3.3

3.6

3.9

4.2

4.5

4.8

C004

V_IN(V)

Figure 3. Flash LED Current Line Regulation @ f_SW= 2MHz

Figure 4. Flash LED Current Line Regulation @ f_SW= 4MHz

0.8

0.7

0.6

0.5

0.4

2

I_CL= 1.7A

1.9

1.8

1.7

1.6

1.5

1.4

1.3

1.2

1.1

1

0.3

0.2

0.1

0

D1,+25°C

D2,+25°C

D1,-40°C

D2,-40°C

D1,+85°C

D2,+85°C

2MHz,+25 C

2MHz,-40 C

2MHz,+85 C

0

1

2

3

4

5

6

7

8

9

10 11 12 13 14 15

C006

Flash Code (#)

2.5

3

3.5

4

4.5

5

5.5

C008

V_IN(V)

Figure 5. Flash LED Current vs Brightness Code

Figure 6. Input Current vs Input Voltage, I_FLASH= 1.5A

2

I_CL= 1.7A

I_CL= 1.9A

1.9

1.8

1.7

1.6

1.5

1.4

1.3

1.2

1.1

1

1.9

1.8

1.7

1.6

1.5

1.4

1.3

1.2

1.1

1

4MHz,+25 C

4MHz,-40 C

4MHz,+85 C

2MHz,+25 C

2MHz,-40 C

2MHz,+85 C

2.5

3

3.5

4

4.5

5

5.5

2.5

3

3.5

4

4.5

5

5.5

C008

V_IN(V)

Figure 7. Input Current vs Input Voltage, I_FLASH= 1.5A

Figure 8. Input Current vs Input Voltage, I_FLASH= 1.5A

6

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TYPICAL PERFORMANCE CHARACTERISTICS (continued)

Unless otherwise specified: T_A= 25°C; V_IN= 3.6V; V_EN= VIN; CIN= 10 μF, COUTF= 10 μF, COUTB = 1 μF (50V 0805 case

size); LF = 1 μH; LB = 22 μH.

2

1.9

1.8

1.7

1.6

1.5

1.4

1.3

1.2

1.1

1

3

2.8

2.6

2.4

2.2

2

I_CL= 1.9A

2MHz,+25 C

2MHz,-40 C

2MHz,+85 C

I_CL= 2.5A

1.8

1.6

1.4

1.2

1

4MHz,+25 C

4MHz,-40 C

4MHz,+85 C

2.5

3

3.5

4

4.5

5

5.5

2.5

3

3.5

4

4.5

5

5.5

C008

V_IN(V)

Figure 9. Input Current vs Input Voltage, I_FLASH= 1.5A

Figure 10. Input Current vs Input Voltage, I_FLASH= 1.5A

3

I_CL= 2.5A

4MHz,+25 C

2.8

I_CL= 3.1A

2.8

2.6

2.4

2.2

2

2.6

2.4

2.2

2

4MHz,-40 C

4MHz,+85 C

2MHz,+25 C

2MHz,-40 C

2MHz,+85 C

1.8

1.6

1.4

1.2

1

1.8

1.6

1.4

1.2

1

2.5

3

3.5

4

4.5

5

5.5

2.5

3

3.5

4

4.5

5

5.5

C008

V_IN(V)

Figure 11. Input Current vs Input Voltage, I_FLASH= 1.5A

Figure 12. Input Current vs Input Voltage, I_FLASH= 1.5A

3

100%

I_CL= 3.1A

2.8

f_SW= 2MHz

2.6

90%

80%

70%

60%

50%

2.4

4MHz,+25 C

2.2

4MHz,-40 C

4MHz,+85 C

2

1.8

1.6

1.4

1.2

1

TA = +25 C

TA = +85 C

TA = -40 C

2.5

3

3.5

4

4.5

5

5.5

2.7

3

3.3

3.6

3.9

4.2

4.5

4.8

C008

C016

V_IN(V)

Figure 13. Input Current vs Input Voltage, I_FLASH= 1.5A

Figure 14. Flash LED Efficiency vs Input Voltage

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TYPICAL PERFORMANCE CHARACTERISTICS (continued)

Unless otherwise specified: T_A= 25°C; V_IN= 3.6V; V_EN= VIN; CIN= 10 μF, COUTF= 10 μF, COUTB = 1 μF (50V 0805 case

size); LF = 1 μH; LB = 22 μH.

0.25

0.24

0.23

0.22

0.21

0.2

100%

90%

80%

70%

60%

50%

f_SW= 4MHz

D1, +25°C

D2, +25°C

D1, +85°C

D2, +85°C

D1, -40°C

D2, -40°C

TA = +25 C

TA = +85 C

TA = -40 C

f_SW= 2MHz

2.7

3

3.3

3.6

3.9

4.2

4.5

4.8

C004

V_IN(V)

2.7

3

3.3

3.6

3.9

4.2

4.5

4.8

C016

V_IN(V)

Figure 15. Flash LED Efficiency vs Input Voltage

Figure 16. Torch Current Line Regulation

0.25

0.24

0.23

0.22

0.21

0.2

0.3

0.25

0.2

0.15

0.1

D1,+25°C

D2,+25°C

D1,-40°C

D2,-40°C

D1,+85°C

D2,+85°C

D1, +25°C

D2, +25°C

D1, +85°C

D2, +85°C

D1, -40°C

D2, -40°C

0.05

0

f_SW= 4MHz

2.7

3

3.3

3.6

3.9

4.2

4.5

4.8

0

1

2

3

4

5

6

7

C004

C006

V_IN(V)

Torch Code (#)

Figure 17. Torch Current Line Regulation

Figure 18. Flash LED Torch Current vs Brightness Code

0.02

0.0198

0.0196

0.0194

0.0192

0.019

0.02

0.0198

0.0196

0.0194

0.0192

0.019

0.0188

0.0186

0.0184

0.0182

0.018

D1, +25°C

D1, +85°C

0.0188

0.0186

0.0184

0.0182

0.018

D1, +25°C

D2, +25°C

D1, +85°C

D2, +85°C

D1, -40°C

D2, -40°C

D1, -40°C

f_SW= 500kHz

11 LEDs

f_SW= 1MHz

2x7 LEDs

2.5

2.8

3.1

3.4

3.7

4

4.3

4.6

4.9

5.2

5.5

2.5

3

3.5

4

4.5

5

5.5

C004

V_IN(V)

Figure 19. Backlight LED Current Line Regulate

Single String

Figure 20. Backlight LED Current Line Regulate

Dual String

8

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TYPICAL PERFORMANCE CHARACTERISTICS (continued)

Unless otherwise specified: T_A= 25°C; V_IN= 3.6V; V_EN= VIN; CIN= 10 μF, COUTF= 10 μF, COUTB = 1 μF (50V 0805 case

size); LF = 1 μH; LB = 22 μH.

0.035

0.03

0.025

0.02

0.015

0.01

0.005

0

0.035

0.03

0.025

0.02

0.015

0.01

0.005

0

D1, -40 C

D2, -40 C

D1, +25 C

D2, +25 C

D1, +85 C

D2, +85 C

D1, -40 C

D2, -40 C

D1, +25 C

D2, +25 C

D1, +85 C

D2, +85 C

0

16

32

48

64

80

96

112

128

0

16

32

48

64

80

96

112

128

C020

Brightness Code (#)

Figure 21. Backlight LED Current vs Brightness Code

Exponential

Figure 22. Backlight LED Current vs Brightness Code

Linear

100%

6 LEDs

8 LEDs

10 LEDs

95%

90%

85%

80%

75%

70%

65%

60%

95%

90%

85%

80%

75%

70%

65%

60%

2x4 LEDs

2x5 LEDs

2x6 LEDs

2x7 LEDs

I_LED= 19mA

f_SW= 500kHz.

I_LED= 19mA

f_SW= 500kHz.

2.7

3.1

3.5

3.9

4.3

4.7

5.1

5.5

2.7

3.1

3.5

3.9

4.3

4.7

5.1

5.5

C022

V_IN(V)

Figure 23. Backlight Efficiency vs Input Voltage

Single String

Figure 24. Backlight Efficiency vs Input Voltage

Dual String

100%

95%

90%

85%

80%

75%

70%

65%

60%

55%

50%

100%

95%

90%

85%

80%

75%

70%

65%

60%

55%

50%

I_LED= 19mA

6 LEDs

I_LED= 19mA

8 LEDs

500 kHz.

1 MHz.

500 kHz.

1 MHz.

2.7

3.1

3.5

3.9

4.3

4.7

5.1

5.5

2.7

3.1

3.5

3.9

4.3

4.7

5.1

5.5

C022

V_IN(V)

Figure 25. Backlight Efficiency vs Input Voltage

Single String - 6 LEDs

Figure 26. Backlight Efficiency vs Input Voltage

Single String - 8 LEDs

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TYPICAL PERFORMANCE CHARACTERISTICS (continued)

Unless otherwise specified: T_A= 25°C; V_IN= 3.6V; V_EN= VIN; CIN= 10 μF, COUTF= 10 μF, COUTB = 1 μF (50V 0805 case

size); LF = 1 μH; LB = 22 μH.

100%

95%

90%

85%

80%

75%

70%

65%

60%

55%

50%

100%

95%

90%

85%

80%

75%

70%

65%

60%

55%

50%

I_LED= 19mA

10 LEDs

I_LED= 19mA

2x4 LEDs

500 kHz.

5.1

1 MHz.

5.1

2.7

3.1

3.5

3.9

4.3

4.7

5.5

2.7

3.1

3.5

3.9

4.3

4.7

5.5

C022

V_IN(V)

Figure 27. Backlight Efficiency vs Input Voltage

Single String - 10 LEDs

Figure 28. Backlight Efficiency vs Input Voltage

Dual String - 2x4 LEDs

100%

95%

90%

85%

80%

75%

70%

65%

60%

55%

50%

100%

95%

90%

85%

80%

75%

70%

65%

60%

55%

50%

I_LED= 19mA

2x6 LEDs

I_LED= 19mA

2x5 LEDs

500 kHz.

1 MHz.

500 kHz.

1 MHz.

2.7

3.1

3.5

3.9

4.3

4.7

5.1

5.5

2.7

3.1

3.5

3.9

4.3

4.7

5.1

5.5

C022

V_IN(V)

Figure 29. Backlight Efficiency vs Input Voltage

Dual String - 2x5 LEDs

Figure 30. Backlight Efficiency vs Input Voltage

Dual String - 2x6 LEDs

100%

95%

90%

85%

80%

75%

70%

65%

60%

55%

50%

100

I_LED= 19mA

2x7 LEDs

Duty-Cycle = 50%

I_LED= 19mA

10

1

500 kHz.

1 MHz.

0.1

2.7

3.1

3.5

3.9

4.3

4.7

5.1

5.5

0.01

C022

V_IN(V)

1.E+0

1.E+1

1.E+2

1.E+3

1.E+4

1.E+5

1.E+6

C033

f_PWM(Hz)

Figure 31. Backlight Efficiency vs Input Voltage

Dual String - 2x7 LEDs

Figure 32. PWM Input Filter Response

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TYPICAL PERFORMANCE CHARACTERISTICS (continued)

Unless otherwise specified: T_A= 25°C; V_IN= 3.6V; V_EN= VIN; CIN= 10 μF, COUTF= 10 μF, COUTB = 1 μF (50V 0805 case

size); LF = 1 μH; LB = 22 μH.

0.020

0.018

0.016

0.014

0.012

0.010

0.008

0.006

0.004

0.002

0.000

0.0110

0.0105

0.0100

0.0095

0.0090

500Hz

1kHz

D1, -40C

D2, -40C

D1, +25C

D2, +25C

D1, +85C

D2, +85C

Duty-Cycle = 50%

f_PWM= 50kHz

I_LED-MAX= 19mA

5kHz

10kHz

25kHz

50kHz

100kHz

500kHz

0

20

40

60

80

100

2.7

3.1

3.5

3.9

4.3

4.7

5.1

5.5

C035

C034

Duty Cycle (%)

V_IN(V)

Figure 33. LED Current vs PWM Duty-Cycle

Figure 34. LED Current vs Input Voltage

w/ PWM Enabled

0.0008

0.0007

0.0006

0.0005

0.0004

0.0003

0.0002

0.0001

0

0.0008

0.0007

0.0006

0.0005

0.0004

0.0003

0.0002

0.0001

0

+25C

+85C

-40C

ILED-MAX = 5mA

ILED-MAX = 19mA

ILED-MAX = 29.5mA

I_LED-MAX= 19mA

Brightness Code = 127

PWM Pin = GND

2.7

3.1

3.5

3.9

4.3

4.7

5.1

5.5

2.7

3.1

3.5

3.9

4.3

4.7

5.1

5.5

C036

C037

V_IN(V)

Figure 35. PWM Offset Current vs Input Voltage

Tri-Temp

Figure 36. PWM Offset Current vs Input Voltage

Different Max. LED Current, Brightness Code = 127

2.5

2

2.5

T_A= +25°C

2

1.5

1

T_A= +85°C

1.5

1

T_A= -40°C

T_A= +25°C and -40°C

0.5

0

0.5

0

2.5

3

3.5

4

4.5

5

5.5

2.5

3

3.5

4

4.5

5

5.5

C001

V_IN(V)

Figure 37. Shutdown Current vs. V_IN

EN = 0V

Figure 38. Standby Current vs. V_IN

EN = VIN

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TYPICAL PERFORMANCE CHARACTERISTICS (continued)

Unless otherwise specified: T_A= 25°C; V_IN= 3.6V; V_EN= VIN; CIN= 10 μF, COUTF= 10 μF, COUTB = 1 μF (50V 0805 case

size); LF = 1 μH; LB = 22 μH.

16

T_A= +25°C

14

T_A= -40°C

12

10

8

6

4

T_A= +85°C

2

0

2.5

3

3.5

4

4.5

5

5.5

C001

V_IN(V)

Figure 39. Standby Current vs. V_IN

EN = 1.8V

FUNCTIONAL DESCRIPTION

Flash and Backlight Enable (EN)

The LM3639A operates from a 2.5V to 5.5V input voltage (IN). EN must be pulled high to bring the LM3639A out

of shutdown. Once EN is high the flash driver and backlight driver can be enabled via the I²C-compatible

interface.

Thermal Shutdown

The LM3639A features a thermal shutdown. When the die temperature reaches 140°C the flash boost, backlight

boost, flash LED current sources, and backlight current sinks shut down.

Flash LED Boost Operation

The LM3639A’s low-voltage boost provides the power for a single flash LED at up to 1.5A or dual flash LEDs at

up to 750 mA each. The device incorporates a 2MHz or 4MHz constant frequency-synchronous boost converter,

and two high-side current sources to regulate the LED currents from a 2.5V to 5.5V input voltage range. The

boost converter switches and maintains at least V_HRacross each of the current sources (FLED1 and FLED2).

This minimum headroom voltage ensures that the current source remains in regulation. If the input voltage is

above the LED voltage + current source headroom voltage, the device does not switch and turns the PFET on

continuously (Pass mode). In Pass mode the difference between (V_IN– I_LEDx R_PMOS) and the voltage across the

LED is dropped across each of the current sources. The LM3639A has a hardware Flash Enable input

(STROBE) and a Flash Interrupt input (TX) designed to interrupt the flash pulse during high battery current

conditions. Both logic inputs have internal 300 kΩ (typ.) pull-down resistors to GND. Additional features of the

LM3639A include an input voltage monitor that can reduce the Flash current (during V_INunder voltage

conditions). Control of the LM3639A’s flash driver is done via the I²C-compatible interface.

Startup (Enabling the FLASH LED Boost)

On startup, when VOUT is less than VIN, the internal synchronous PFET turns on as a current source and

delivers 200 mA (typ.) to the output capacitor. During this time the current source (LED) is off. When the voltage

across the output capacitor reaches 2.2V (typ.) the current sources will turn on. At turn-on the current sources

will step through each FLASH or TORCH level until the target LED current is reached. This gives the device a

controlled turn-on and limits inrush current from the VIN supply.

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Pass Mode

The LM3639A starts up in Pass Mode and stays there until Boost Mode is needed to maintain regulation. If the

voltage difference between VOUT and VLED falls below VHR, the device switches to Boost Mode. In Pass Mode

the boost converter does not switch, and the synchronous PFET turns fully on bringing VOUT up to VIN – ILED x

RPMOS.

Flash Mode Currents

There are 16 programmable flash current levels for FLED1 and FLED2 from 46.875 mA to 750 mA. Flash mode

is activated via the I²C-compatible interface or by pulling the STROBE pin HIGH (LOW if configured as Active-

Low). Once the Flash sequence is activated the current sources will ramp up to their programmed Flash current

by stepping through all current steps until the programmed current is reached.

Table 1. Flash Current vs. Code

Code 0000 = 46.875 mA

Code 0001 = 93.75 mA

Code 0010 =140.625 mA

Code 0011 = 187.5 mA

Code 0100 = 234.375 mA

Code 0101 = 281.25 mA

Code 0110 = 328.125 mA

Code 0111 = 375 mA

Code 1000 = 421.875 mA

Code 1001 = 468.75 mA

Code 1010 = 515.625 mA

Code 1011 = 562.5 mA

Code 1100 = 609.375 mA

Code 1101 = 656.25 mA

Code 1110 = 703.125 mA

Code 1111 = 750 mA

Torch Mode

Torch mode is activated through the I²C-compatible interface setting or by the hardware STROBE input when the

Strobe EN bit is set to '1'. Once Torch mode is enabled the current sources will ramp up to the programmed

Torch current level.

Table 2. Torch Current vs. Code

Code 000 = 28.125 mA

Code 001 = 56.25 mA

Code 010 = 84.375 mA

Code 011 = 112.5 mA

Code 100 = 140.625 mA

Code 101 = 168.75 mA

Code 110 = 196.875 mA

Code 111 = 225 mA

Independent LED Control

The part has the ability to independently turn on and turn off the FLED1 or FLED2 current sources. The LED

current is adjusted by writing to the Torch Brightness or Flash Brightness Registers. Both the FLED1 or FLED2

use the same target current level stored in the Torch Brightness and the Flash Brightness Registers. Both LED

outputs use the same LED ramp step time.

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Power Amplifier Synchronization (TX)

The TX pin is a Power Amplifier Synchronization input. This is designed to reduce the flash LED currents and

thus limit the battery-current during high battery current conditions such as PA transmit events. When the

LM3639A is engaged in a Flash event and the TX pin is pulled high, the LED current is forced into Torch mode at

the programmed Torch current setting. If the TX pin is then pulled low before the Flash pulse terminates, the LED

current will return to the previous Flash current level. At the end of the Flash time-out, whether the TX pin is high

or low, the LED current will turn off. The TX pin has a 300 kΩ pull-down resistor connected to GND.

Input Voltage Flash Monitor (IVFM)

The LM3639A has the ability to adjust the flash current based upon the voltage level present at the VIN pin

utilizing an Input Voltage Flash Monitor. The adjustable VIN Monitor threshold ranges from 2.5V to 3.2V in 100

mV steps. Depending on the option, the LM3639A will either transition the LED current to the programmed Torch

current or shut down completely when the Input Voltage Monitor detects an input voltage drop lower than the

threshold value.

Flash LED Fault/Protections

Flash Timeout

The Flash Timeout period sets the maximum amount of time that the Flash Currents is sourced from each of the

current source (FLED1 and FLED2). The LM3639A has 32 timeout levels ranging 32 ms to 1024 ms in 32 ms

steps. Flash Timeout only applies to the Flash Mode operation. In I²C-compatible Flash Mode, the flash period is

equal to the timeout value. In Strobe Flash Mode, the flash period is set by the active duration of the Strobe pin if

the duration is less than the timeout value. If the Strobe event lasts longer than the set flash timeout value, the

flash event will terminate upon reach the timeout period.

Over-Voltage Protection (OVP)

The output voltage is limited to typically 5.0V (see V_OVPSpec). In situations such as an open LED, the LM3639A

will raise the output voltage in order keep the LED current at its target value. When V_OUTFreaches 5.0V (typ.) the

over-voltage protection (OVP) comparator will trip and turn off the internal NFET. When V_OUTFfalls below the

“V_OVPOff Threshold”, the LM3639A will begin switching again. The mode bits in the Enable Register (0x0A) are

not cleared upon an OVP event.

Current Limit

The LM3639A features selectable inductor current limits. When the inductor current limit is reached, the

LM3639A will terminate the charging phase of the switching cycle. Since the current limit is sensed in the NMOS

switch, there is no mechanism to limit the current when the device operates in Pass Mode. In Boost mode or

Pass mode, if OUTF falls below 2.3V, the part stops switching, and the PFET operates as a current source

limiting the current to 200 mA. This prevents damage to the LM3639A and excessive current draw from the

battery during output short-circuit conditions. Pulling additional current from the OUTF node during normal

operation is not recommended.

LED and/or OUTF Fault

The LM3639A determines an LED open condition if the OVP threshold is crossed at the OUTF pin while the

device is in Flash or Torch mode. An LED short condition is determined if the voltage at LED goes below 500 mV

(typ.) while the device is in Torch or Flash mode. There is a delay of 256 μs deglitch time before the LED flag is

valid and 2.048 ms before the VOUT flag is valid. This delay is the time between when the Flash or Torch current

is triggered and when the LED voltage and the output voltage are sampled.

Backlight Boost Operation

The high-voltage boost converter provides power for the two current sinks (BLED1 and BLED2). The backlight

boost operates using a 10 µH to 22 µH inductor and a 1µF output capacitor. The selectable 500 kHz or 1 MHz

switching frequency allows use of small external components and provides for high boost converter efficiency.

When there are different voltage requirements in both high-voltage LED strings, the LM3639A’s backlight boost

will regulate the feedback point of the highest voltage string to 400 mV and drop the excess voltage of the lower

voltage string across its current sink.

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Backlight Over-Voltage Protection

The output voltage protection is limited to typically 16V, 24V, 32V or 40V (see VOVP Spec). In situations such as

an open LED, the LM3639A will raise the output voltage in order to keep the LED current at its target value.

When VOUTB reaches the selected OVP level, the over-voltage comparator will trip and turn off the internal

NFET. When VOUT falls below the “VOVP Off Threshold”, the LM3639A will begin switching again. By default,

the Backlight OVP flag in the Flag Register (0x0B, Bit7) will not be set upon hitting an OVP condition. To enable

this reporting feature, the BL Flag Report bit (Register 0x09, Bit7) must be set to a '1'. The BL Flag Report

function is intended for use in a factory environment to check for LED connectivity and is not intended for use

during normal operation.

Backlight LED Short Detection

The LM3639A features a Backlight LED short flag that indicates whether either of the BLEDx pins rise above

(VIN - 1V). This detection block can help detect whether one or more of the LEDs in a string have experienced a

short when operating in a balanced dual-string LED configuration (ex: 2 strings of 5 is balanced. One string of 5

and one string of 4 is unbalanced). If one or more of the LEDs in a string become shorted, and either of the

BLEDx pins rise above (VIN - 1V), the BLED1/2 Flag in the Flag register (0x0B, Bit2) will be set to a '1'. By

default this detection block is disabled. To enable this reporting feature, the BL Flag Report bit (Register 0x09,

Bit7) must be set to a '1'. The BL Flag Report function is intended for use in a factory environment to check for

LED connectivity and is not intended for use during normal operation.

Backlight Current Sinks (B_LED1and B_LED2

)

BLED1 and BLED2 control the current in the backlight boost LED strings. Each current sink has 3-bit full-scale

current programmability and 7-bit brightness control. Either current sink can have its current set through a

dedicated brightness register and be controlled via the PWM input.

Backlight Boost Switching Frequency

The LM3639A’s backlight boost converter can have a 500 kHz or 1 MHz switching frequency. For the 500 kHz

switching frequency selection the inductor must be 22 µH. For the 1 MHz switching frequency selection the

inductor can be 10 µH or 22 µH.

PWM Input

There is a single PWM input which can control the current in the backlight current sinks (BLED1/2). When the

PWM input is enabled, the current becomes a function of the full-scale current, the brightness code, and the

PWM input duty cycle. The PWM pin has a 300 kΩ pull-down resistor connected to GND.

PWM Polarity

The PWM input can be programmed to have active high or active low polarity.

Full-Scale Current

There are 8 (3-bit) separate full-scale current settings for the backlight current. The full-scale current is the

maximum backlight current when the brightness code is at 100% (Code 0x7F). The full-scale current vs full-scale

current code is given by:

I_LEDFullscale = 5mA + (CODE × 3.5 mA)

(1)

Table 3. Full-Scale Current vs. Code

Code

000

001

:

Full Scale Current

5 mA

8.5 mA

:

100

:

19 mA

:

110

111

26 mA

29.5 mA

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LED Current Mapping Modes

The backlight current can be programmed for either exponential or linear mapping modes. These modes

determine the transfer characteristic of backlight code to LED current. The brightness code selected for linear will

always be forced to be equal to the exponential value. The brightness code for exponential will always be

mapped to the linear code as well.

Exponential Mapping

In exponential mapping mode the brightness code to backlight current transfer function is given by the equation:

»

ÿ

Code +1

≈

’

44-

∆

÷

…

Ÿ

2.91

Ÿ

◊

⁄

I_LED= I_{LED_FULLSCALE}x D_PWMx 0.85^…

«

(2)

where I_{LED_FULLSCALE}is the full-scale LED current setting, Code is the backlight code in the brightness register,

and D_PWMis the PWM input duty cycle. In exponential mapping mode the current ramp (either up or down)

appears to the human eye as a more uniform transition then the linear ramp. This is due to the logarithmic

response of the eye. NOTE: Code '0' does not enable the boost or the current sinks and should not be

used.

Linear Mapping

In linear mapping mode the brightness code to backlight current has a linear relationship and follows the

equation:

1

I_LED= I_{LED_FULLSCALE}

x

x Code x D_PWM

127

(3)

where I_{LED_FULLSCALE}is the full-scale LED current setting, Code is the backlight code in the brightness register,

and D_PWMis the PWM input duty cycle. NOTE: Code '0' does not enable the boost or the current sinks and

should not be used.

LED Current Ramping

Ramp-Up/Ramp-Down Step Time

The Ramp-Up step time is the time the LM3639A spends at each current step during the ramping up of the

backlight LED current. The Ramp-Down step time is the time the LM3639A spends at each current step during

the ramping down of the backlight LED current. There are 8 different Ramp-Up and 8 different Ramp-Down step

times. The Ramp-Up and Ramp-Down step times are independently programmable, but not independently

programmable for each backlight current sink. For example, programming a Ramp-Up or Ramp-Down time

programs the same ramp time for the current in both BLED1 and BLED2.

Table 4. Ramp Times

Code

000

001

010

011

100

101

110

111

Ramp-Up Step Time

32 µs

Ramp-Down Step Time

32 µs

4.096 ms

8.192 ms

16.384 ms

32.768 ms

65.536 ms

131.072 ms

262.144 ms

16.384 ms

32.768 ms

65.536 ms

131.072 ms

262.144 ms

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APPLICATION INFORMATION

Register Map (7-Bit I²C Chip Address = 0x39)

0x00

0x01

[7:0]

Device ID

0x00 0001 0001

0x01 0000 1001

Check sum

BACKLIGHT CONFIGURATION REGISTERS

[7]

N/A

00 = 16V

01 = 24V (default)

10 = 32V

[6:5]

BLED OVP

11 = 40V

BLED

Mapping mode

0 = Exponential

1 = Linear (default)

0x02

[4]

[3]

0 = Active high (default)

1 = Active low

BLED PWM configuration

BLED Max Current

000 - 5 mA

[2:0]

100 19 mA Default

111 - 29.5 mA

[7]

[6]

RFU

Must ALWAYS be set to a '0'

0 = 500 kHz (default)

1 = 1 Mhz

BLED SW Frequency

000 = 32 µs per step

~

111 = 262 ms per step

BLED Brightness

Ramp Fall Rate

0x03

[5:3]

[2:0]

000 = 32 µs per step

~

111 = 262 ms per step

BLED Brightness

Ramp rise Rate

[7]

[6:0]

[7]

N/A

-

0x04

0x05

BLED

Brightness control

128 step (7-bit) (Exponential)

N/A

-

BLED

Brightness control

[6:0]

128 step (7-bit) (Linear)

Any code written to Register 0x04 will be mapped to 0x05.

Any code written to Register 0x05 will be mapped to 0x04

Writing a '0' to either Register 0x04 or 0x05 is not recommended as the LM3639A will remain off.

FLASH CONFIGURATION REGISTERS

7

N/A

000 = 28.125 mA

~

[7:4]

FLED LED1/2 Torch current

0x06

111 = 225 mA

0000 = 46.875 mA

~

[3:0]

FLED LED1/2 strobe Current

1111 = 750 mA

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0 = 2 MHz (default)

1 = 4 MHz

[7]

FLED SW Frequency

00 = 1.7A

01 = 1.9A

FLED

Current Limit

[6:5]

0x07

10 = 2.5A (default)

11 = 3.1A

00000 = 32 ms

01111 = 512 ms (default)

11111 = 1024 ms

FLED

Strobe Time-Out

[4:0]

[7:3]

N/A

000 = 2.5V

001 = 2.6V

. . .

0x08

FLED

V_INmonitor

[2:0]

110 = 3.1V

111 = 3.2V

I/O CONTROL REGISTER

1 = Backlight OVP and BLED1/2 Short Flag Reporting ACTIVE

[7]

Backlight Flag Reporting

0 = Backlight OVP and BLED1/2 Short Flag Reporting DISABLED

(default)

1= PWM Enabled

0 = PWM Ignored

1 = Active High

0 = Active Low

1 = Strobe Flash

0 = I²C Flash

[6]

[5]

[4]

[3]

[2]

[1]

[0]

PWM ENABLE

STROBE POLARITY

STROBE EN

0x09

1 = Active High

0 = Active Low

1 = Tx Enabled

0 = Tx Ignored

1 = Standby

TX POLARITY

TX Enable

VIN Monitor Mode

VIN Monitor EN

0 = Torch

1 = VIN Monitor Enabled

0 = Disabled

ENABLE REGISTER

1 = RESET

[7]

[6]

[5]

[4]

[3]

[2]

[1]

[0]

Software Reset

FLED1 EN

0 = disable (auto)

1 = Flash LED1 On

0 = Disabled

1 = Flash LED2 On

0 = Disabled

FLED2 EN

1 = Backlight LED1 On

0 = Disabled

BLED1 EN

0x0A

1 = Backlight LED2 On

0 = Disabled

BLED2 EN

1 = FLASH

Torch/Flash

FLASH EN

0 = TORCH

1 = Enable FLASH

0 = Off

1 = Enable Backlight

0 = Off

BACKLIGHT EN

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Setting both "FLED1 EN" and "FLED2 EN" to '0' when "FLASH EN" is '1' is not recommended as the flash boost will run in OVP

Setting both "BLED1 EN" and "BLED2 EN" to '0' when "BACKLIGHT EN" is '1' is not recommended backlight boost will run in OVP.

See Notes for more configuration details.

FLAGS REGISTER

1 = FAULT

[7]

[6]

[5]

[4]

[3]

[2]

[1]

[0]

BACKLIGHT OVP

FLASH OVP

0 = NORMAL

1 = FAULT

0 = NORMAL

1 = FAULT

FLASH OUTPUT SHORT

VIN MONITOR

0 = NORMAL

1 = VIN Monitor Threshold Crossed

0 = Normal

0x0B

1 = TX Event Occurred

0 = Normal

TX INTERRUPT

1 = FAULT

FLED1/2 SHORT

BLED1/2 SHORT

THERMAL SHUTDOWN

0 = NORMAL

1 = FAULT

0 = NORMAL

1 = Thermal Shutdown

0 = Normal

Notes

1. To initiate a flash event, the Flash EN bit must be set via I²C (Reg 0x0A, bit 1 = ‘1’). Upon the termination of

a flash event (I²C Controlled or Strobe Controlled), the Flash EN bit in register 0x0A will automatically clear

itself to ‘0’. To restart a flash event, the Flash EN bit must be reset to a ‘1’ via an I²C write.

2. During Backlight Operation, registers 0x02 and 0x03 become READ-ONLY. To adjust the values of registers

0x02 and 0x03, the Backlight EN bit in register 0x0A must be set to a ‘0’ first.

3. During Flash Operation, register 0x07 becomes READ-ONLY. To adjust the values of register 0x07, the

Flash EN bit in register 0x0A must be set to a ‘0’ first.

4. If a single Backlight string is used, the string must be connected to BLED1, and the BLED2 EN bit must be

set to ‘0’. BLED2 in this configuration should be left floating.

5. If a single Flash LED is going to be used without shorting FLED1 to FLED2, FLED1 must be used and the

FLED2 EN bit must be set to a ‘0’. FLED2 in this configuration should be left floating.

Applications Information: Backlight

Backlight Inductor Selection

The LM3639A is designed to work with a 10 µH to 22 µH inductor. When selecting the inductor, ensure that the

saturation rating is high enough to accommodate the applications peak inductor current. The inductance value

must also be large enough so that the peak inductor current is kept below the LM3639A's switch current limit.

Table 5 lists various inductors that can be used with the LM3639A. The inductors with higher saturation currents

are more suitable for applications with higher output currents or voltages (multiple strings). The smaller devices

are geared toward single string applications with lower series LED counts.

NOTE

For high LED count single string applications (greater than 9 LEDs), the 500 kHz switching

frequency and a 22 µH inductor must be used. For dual string applications with a

maximum LED count of two strings of 7 LEDs, a 22 µH inductor is required for use with

the 500kHz switching frequency, whereas a 10 µH or a 22 µH inductor can be used with

the 1 MHz switching frequency.

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Table 5. Inductors

Manufacturer

TDK

Part Number

Value

22µH

Size

Current Rating

600 mA

DC Resistance

VLF403212MT-220M

VLS252010T-100M

VLS2012ET-100M

VLF301512MT-100M

VLF4010ST-100MR80

VLS252012T-100M

VLF3014ST-100MR82

VLF4014ST-100M1R0

XPL2010-103ML

4 mm × 3.2 mm × 1.2 mm

2.5 mm × 2 mm × 1 mm

2 mm × 2 mm × 1.2 mm

3.0 mm × 2.5 mm × 1.2mm

2.8 mm × 3 mm × 1 mm

2.5 mm × 2 mm × 1.2mm

2.8 mm × 3 mm × 1.4mm

3.8 mm × 3.6 mm × 1.4 mm

1.9 mm × 2 mm × 1 mm

0.59Ω

0.712Ω

0.47Ω

0.25Ω

0.63Ω

0.25Ω

0.22Ω

0.56Ω

0.54Ω

TDK

10 µH

590 mA

TDK

695 mA

TDK

690 mA

TDK

800 mA

TDK

810 mA

TDK

820 mA

TDK

1000 mA

610 mA

Coilcraft

LPS3010-103ML

2.95 mm × 2.95 mm × 0.9

mm

550 mA

Coilcraft

LPS4012-103ML

LPS4012-223ML

LPS4018-103ML

LPS4018-223ML

10 µH

22 µH

10 µH

22 µH

3.9mm × 3.9mm × 1.1mm

3.9 mm × 3.9 mm × 1.1 mm

3.9 mm × 3.9 mm × 1.7 mm

1000 mA

780 mA

1100 mA

700 mA

0.35Ω

0.6Ω

0.2Ω

0.36Ω

Backlight Output Capacitor Selection

The LM3639A’s output capacitor has two functions: to filter the boost converter's switching ripple, and to ensure

feedback loop stability. As a filter, the output capacitor supplies the LED current during the boost converter's on

time and absorbs the inductor's energy during the switch's off time. This causes a sag in the output voltage

during the on time and a rise in the output voltage during the off time. Because of this, the output capacitor must

be sized large enough to filter the inductor current ripple that could cause the output voltage ripple to become

excessive. As a feedback loop component, the output capacitor must be at least 1 µF and have low ESR;

otherwise, the LM3639A's boost converter can become unstable. This requires the use of ceramic output

capacitors. Table 6 lists part numbers and voltage ratings for different output capacitors that can be used with the

LM3639A.

NOTE

For all LED applications, it is required that at least 0.4 µF of capacitance is present at the

output of the backlight boost converter. Please refer to the output capacitor data sheets to

find the effective capacitance (taking into account the DC Bias effect) of the capacitors at

the target application output voltage.

Table 6. Output Capacitors

Manufacturer

TDK

Part Number

Value

1 µF

Size

0805

Rating

50V

Description

COUT

CGA4J3X7R1H105K

GRM21BR71H105KA12

Murata

1 µF

50V

COUT

20

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Backlight Diode Selection

The diode connected between SW and OUT must be a Schottky diode and have a reverse breakdown voltage

high enough to handle the maximum output voltage in the application. Table 7 lists various diodes that can be

used with the LM3639A.

Table 7. Diodes

Manufacturer

Diodes Inc.

Part Number

B0540WS

Value

Size

Rating

Schottky

SOD-323

40V/500 mA

40V/200 mA

40V/250 mA

Diodes Inc.

SDM20U40

SOD-523 (1.2 mm × 0.8 mm × 0.6 mm)

On Semiconductor

NSR0340V2T1G

NSR0240V2T1G

Backlight Layout Guidelines

The LM3639A contains an inductive boost converter which sees a high switched voltage (up to 40V) at the SWB

pin, and a step current (up to 1A) through the Schottky diode and output capacitor each switching cycle. The high

switching voltage can create interference into nearby nodes due to electric field coupling (I = CdV/dt). The large

step current through the diode and the output capacitor can cause a large voltage spike at the SW pin and the

OVP pin due to parasitic inductance in the step current conducting path (V = LdI/dt). Board layout guidelines are

geared towards minimizing this electric field coupling and conducted noise. Figure 40 highlights these two noise

generating components.

Voltage Spike

V_OUT+ V_FSchottky

Pulsed voltage at SW

Current through

I

Schottky Diode and C_OUT

PEAK

I

= I

IN

AVE

Paracitic

Current through

inductor

Circuit Board

Inductances

Affected Node

due to capacitive

coupling

Cp1

L(B)

Lp1

Lp2

D1

Up to 40V

C_OUTB

2.7V to 5.5V

SW

V_LOGIC

IN

Lp3

10 kW

SCL

SDA

OVP

LM3639A

LCD Display

BLED1

BLED2

GND

Figure 40. LM3639A's Boost Converter Showing Pulsed Voltage at SW (High dV/dt) and Current Through

Schottky and COUT (High dI/dt)

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The following lists the main (layout sensitive) areas of the LM3639A in order of decreasing importance:

Output Capacitor

•

Schottky Cathode to COUTB+

COUTB− to GND

Schottky Diode

•

SWB Pin to Schottky Anode

Schottky Cathode to COUTB+

Inductor

•

SWB Node PCB capacitance to other traces

Input Capacitor

•

CIN+ to VIN pin

CIN− to GND

Backlight Output Capacitor Placement

The output capacitor is in the path of the inductor current discharge current. As a result, C_OUTBsees a high

current step from 0 to I_PEAKeach time the switch turns off and the Schottky diode turns on. Typical turn-off/turn-

on times are around 5 ns. Any inductance along this series path from the cathode of the diode through C_OUTB

and back into the LM3639A's GND pin will contribute to voltage spikes (V_SPIKE= L_PX× dI/dt) at SWB and OUTB

which can potentially over-voltage the SWB pin, or feed through to GND. To avoid this, C_OUTB+ must be

connected as close as possible to the cathode of the Schottky diode, and C_OUT− must be connected as close as

possible to the LM3639A's GND bump. The best placement for C_OUTBis on the same layer as the LM3639A to

avoid any vias that will add extra series inductance.

Schottky Diode Placement

The Schottky diode is in the path of the inductor current discharge. As a result the Schottky diode sees a high

current step from 0 to I_PEAKeach time the switch turns off and the diode turns on. Any inductance in series with

the diode will cause a voltage spike (V_SPIKE= L_PX× dI/dt) at SW and OUT which can potentially over-voltage the

SW pin, or feed through to VOUT and through the output capacitor and into GND. Connecting the anode of the

diode as close as possible to the SW pin and the cathode of the diode as close as possible to COUT+ will

reduce the inductance (L_PX) and minimize these voltage spikes.

Backlight Inductor Placement

The node where the inductor connects to the LM3639A’s SW bump presents two challenges. First, a large

switched voltage (0 to V_OUT+ V_{F_SCHOTTKY}) appears on this node every switching cycle. This switched voltage

can be capacitively coupled into nearby nodes. Second, there is a relatively large current (input current) on the

traces connecting the input supply to the inductor and connecting the inductor to the SW bump. Any resistance in

this path can cause large voltage drops that will negatively affect efficiency.

To reduce the capacitively coupled signal from SWB into nearby traces, the SW bump-to-inductor connection

must be minimized in area. This limits the PCB capacitance from SW to other traces. Additionally, other nodes

need to be routed away from SWB and not directly beneath. This is especially true for high-impedance nodes

that are more susceptible to capacitive coupling such as (SCL, SDA, EN, PWM). A GND plane placed directly

below SWB will help isolate SWB and dramatically reduce the capacitance from SW into nearby traces.

To limit the trace resistance of the VBATT-to-inductor connection and from the inductor-to-SW connection, use

short, wide traces.

Input Capacitor Selection and Placement

The input bypass capacitor filters the inductor current ripple, and the internal MOSFET driver currents, during

turn-on of the power switch.

The driver current requirement can be a few hundred mAs with 5 ns rise and fall times. This will appear as high

dI/dt current pulses coming from the input capacitor each time the switch turns on. Close placement of the input

capacitor to the IN pin and to the GND pin is critical since any series inductance between VIN and C_IN+ or C_IN−

and GND can create voltage spikes that could appear on the V_INsupply line and in the GND plane.

22

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Close placement of the input bypass capacitor at the input side of the inductor is also critical. The source

impedance (inductance and resistance) from the input supply, along with the input capacitor of the LM3639A,

form a series RLC circuit. If the output resistance from the source (R_S) is low enough the circuit will be

underdamped and will have a resonant frequency (typically the case). Depending on the size of L_Sthe resonant

frequency could occur below, close to, or above the LM3639A's switching frequency. This can cause the supply

current ripple to be:

•

approximately equal to the inductor current ripple when the resonant frequency occurs well above the

LM3639A's switching frequency;

•

greater then the inductor current ripple when the resonant frequency occurs near the switching frequency; or

less then the inductor current ripple when the resonant frequency occurs well below the switching frequency.

Figure 41 shows the series RLC circuit formed from the output impedance of the supply and the input capacitor.

The circuit is re-drawn for the AC case where the V_INsupply is replaced with a short to GND, and the LM3639A +

Inductor is replaced with a current source (ΔI_L).

Equation 1 is the criteria for an underdamped response. Equation 2 is the resonant frequency. Equation 3 is the

approximated supply current ripple as a function of L_S, R_S, and C_IN.

As an example, consider a 3.6V supply with 0.1Ω of series resistance connected to C_INthrough 50 nH of

connecting traces. This results in an underdamped input filter circuit with a resonant frequency of 712 kHz. Since

the switching frequency lies near to the resonant frequency of the input RLC network, the supply current is

probably larger then the inductor current ripple. In this case, using Equation 3 from Figure 41, the supply current

ripple can be approximated as 1.68 times the inductor current ripple. Increasing the series inductance (L_S) to 500

nH causes the resonant frequency to move to around 225 kHz and the supply current ripple to be approximately

0.25 times the inductor current ripple.

I

SUPPLY

DI

L

R

S

L

S

SW

IN

V

IN

LM3639A

Supply

C

IN

I

SUPPLY

R

S

L

S

C

IN

DI

L

2

R_S

4 x L_S²

1

1.

>

L_Sx C_IN

1

2.

3.

f_RESONANT

=

2p L_Sx C_IN

1

2p x 500 kHz x C_IN

D

_Lx

I_SUPPLYRIPPLEö I

2

≈

’

÷

◊

1

2

∆

R_S+ 2p x 500kHz x L_S

-

∆

x

2p 500 kHz C_IN

«

Figure 41. Input RLC Network

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Applications Information: Flash

Output Capacitor Selection

The LM3639A's flash boost converter is designed to operate with a ceramic output capacitor of at least 10 µF.

When the boost converter is running, the output capacitor supplies the load current during the boost converter's

on-time. When the NMOS switch turns off, the inductor energy is discharged through the internal PMOS switch,

supplying power to the load and restoring charge to the output capacitor. This causes a sag in the output voltage

during the on-time and a rise in the output voltage during the off-time. The output capacitor is therefore chosen to

limit the output ripple to an acceptable level depending on load current and input/output voltage differentials and

also to ensure the converter remains stable.

Larger capacitors such as a 22 µF or capacitors in parallel can be used if lower output voltage ripple is desired.

To estimate the output voltage ripple considering the ripple due to capacitor discharge (ΔV_Q) and the ripple due

to the capacitors ESR (ΔV_ESR) use the following equations:

For continuous conduction mode, the output voltage ripple due to the capacitor discharge is:

(

)

I_LEDx V_OUT- V

IN

DV_Q=

f_SWx V_OUTx C_OUT

(4)

(5)

The output voltage ripple due to the output capacitors ESR is found by:

I_LEDx V_OUT

≈

«

’

◊

+DI_L

DV_ESR= R_ESR

x

V_IN

where

(

)

V

x V_OUT- V

IN

DI_L=

2x f_SWx L x V_OUT

In ceramic capacitors the ESR is very low so the assumption is that 80% of the output voltage ripple is due to

capacitor discharge and 20% from ESR. Table 8 lists different manufacturers for various output capacitors and

their case sizes suitable for use with the LM3639A.

Input Capacitor Selection

Choosing the correct size and type of input capacitor helps minimize the voltage ripple caused by the switching

of the LM3639A’s boost converter, and reduces noise on the boost converter's input terminal that can feed

through and disrupt internal analog signals. In the Typical Application Circuit a 10 µF ceramic input capacitor

works well. It is important to place the input capacitor as close as possible to the LM3639A’s input (IN) terminal.

This reduces the series resistance and inductance that can inject noise into the device due to the input switching

currents. The table below lists various input capacitors recommended for use with the LM3639A.

Table 8. Recommended Flash Input/Output Capacitors (X5R/X7R Dielectric)

Manufacturer

Murata

Part Number

GRM155R60J106ME44D

C1608JB0J106M

Value

10 µF

Case Size

Voltage Rating

0402 (1mm × 0.5mm × 0.5mm)

0603 (1.6 mm × 0.8 mm × 0.8 mm)

0805 (2 mm × 1.25 mm × 1.25 mm)

0603 (1.6 mm x 0.8 mm x 0.8 mm)

0805 (2 mm × 1.25 mm × 1.25 mm)

6.3V

10V

6.3V

10V

TDK Corporation

Murata

C2012JB1A106M

GRM188R60J106M

GRM21BR61A106KE19

Murata

Inductor Selection

The LM3639A's flash boost is designed to use a 1 µH or 0.47 µH inductor. Table 9 below lists various inductors

and their manufacturers that work well with the LM3639A. When the device is boosting (V_OUT> V_IN) the inductor

will typically be the largest area of efficiency loss in the circuit. Therefore, choosing an inductor with the lowest

possible series resistance is important. Additionally, the saturation rating of the inductor should be greater than

the maximum operating peak current of the LM3639A. This prevents excess efficiency loss that can occur with

inductors that operate in saturation. For proper inductor operation and circuit performance, ensure that the

inductor saturation and the peak current limit setting of the LM3639A are greater than I_PEAKin the following

calculation:

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( )

_INx V_OUT- V

IN

I_LOADV_OUT

V

I_PEAK

=

x

+DI_L

where

DI_L=

h

V

2 x f_SWx L x V_OUT

IN

(6)

where ƒ_SW= 4 MHz or 2MHz, and efficiency can be found in the Typical Performance Characteristics plots.

Table 9. Recommended Inductors

Manufacturer

L

Part Number

DFE201612C-H-1R0M

DFE252010C

Dimensions (LxWxH)

2 mm x 1.6 mm x 1.2 mm

2.5 mm x 2 mm x 1 mm

2.5 mm x 2 mm x 1.2 mm

I_SAT

3.1A

3.4A

3.8A

R_DC

68 mΩ

60 mΩ

45 mΩ

TOKO

1µH

DFE252012C

Flash Layout Recommendations

The high switching frequency and large switching currents of the LM3639A make the choice of layout important.

The following steps should be used as a reference to ensure the device is stable and maintains proper LED

current regulation across its intended operating voltage and current range.

1. Place C_INon the top layer (same layer as the LM3639A) and as close to the device as possible. The input

capacitor conducts the driver currents during the low-side MOSFET turn-on and turn-off and can see current

spikes over 1A in amplitude. Connecting the input capacitor through short, wide traces to both the VIN and

GND terminals will reduce the inductive voltage spikes that occur during switching which can corrupt the V_IN

line.

2. Place C_OUTFon the top layer (same layer as the LM3639A) and as close as possible to the OUTF and GND

terminals. The returns for both C_INand C_OUTFshould come together at one point, as close to the GND pin as

possible. Connecting C_OUTFthrough short, wide traces will reduce the series inductance on the OUTF and

GND terminals that can corrupt the V_OUTFand GND lines and cause excessive noise in the device and

surrounding circuitry.

3. Connect the inductor on the top layer close to the SWF pin. There should be a low-impedance connection

from the inductor to SWF due to the large DC inductor current, and at the same time the area occupied by

the SW node should be small to reduce the capacitive coupling of the high dV/dt present at SW that can

couple into nearby traces.

4. Avoid routing logic traces near the SWF node to avoid any capacitively coupled voltages from SW onto any

high-impedance logic lines such as STROBE, EN, TX, PWM, SDA, and SCL. A good approach is to insert an

inner layer GND plane underneath the SWF node and between any nearby routed traces. This creates a

shield from the electric field generated at SW.

5. Terminate the Flash LED cathodes directly to the GND pin of the LM3639A. If possible, route the LED

returns with a dedicated path to keep the high amplitude LED currents out of the GND plane. For Flash LEDs

that are routed relatively far away from the LM3639A, a good approach is to sandwich the forward and return

current paths over the top of each other on two layers. This will help reduce the inductance of the LED

current paths.

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MECHANICAL DATA

YFQ0020xxx

D

0.600±0.075

E

TMD20XXX (Rev D)

D: Max = 2.19 mm, Min = 2.13 mm

E: Max = 1.815 mm, Min =1.755 mm

4215083/A

12/12

A. All linear dimensions are in millimeters. Dimensioning and tolerancing per ASME Y14.5M-1994.

B. This drawing is subject to change without notice.

NOTES:

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型号：	LM3639AYFQR
厂家：	TEXAS INSTRUMENTS
描述：	LM3639A 单芯片 40V 背光 + 1.5A LED 闪光灯驱动器 \| YFQ \| 20 \| -40 to 85 驱动闪光灯驱动器
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相关型号：

LM3639AYFQT

LM363AD

LM363AD/A+

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LM363AH-500/A+

LM363AH10

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LM363D

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LM363H-10/A+