FAN5608_06_技术文档

August 2006

FAN5608 Serial / Parallel LED Driver with

Current-Regulated, Step-Up DC/DC Converter

Features

Description

Two independent channels drive up to six LEDs

per channel

The FAN5608 is an integrated Schottky diode LED

driver, which generates regulated output currents from a

battery input voltage of 2.7V to 5V. An internal MOS

switch and the external inductor deliver the necessary

voltage to the load. The proprietary internal

compensation loop continuously monitors the lowest

LED cathode voltage of both channels and adjusts the

V_OUTvoltage to the minimum value. The minimum V_OUT

is determined by the highest LED forward voltage of the

selected channel. This adaptive nature allows the

FAN5608 architecture to deliver high efficiency. Up to

twelve LEDs can be connected in series as long as the

summed forward voltage does not exceed the maximum

specification of 24V. It is not required to match an equal

number of LEDs serially within each channel; FAN5608

delivers the highest efficiency and best current

regulation in the balanced configuration.

Adaptive output voltage drive to maximize efficiency

PFM mode of operation of the boost circuit

Up to 85% efficiency

Up to 2×20mA output

Two built-in DACs for independent (digital) brightness

control for both channels

LED current can be duty-cycle-modulated, 0 to 20mA

Digital, analog, and PWM brightness control

2.7V to 5.5V input voltage range

500KHz operating frequency

Soft-start feature

Low shutdown current: I_CC< 1μA

Open-load protection

Minimal external components needed

Space-saving 4x4mm 12-lead MLP packages

FAN5608 has two internal two-bit D/A converters that

provide independent programmability to each output

channel. In analog programming, "B" pins must be GND

(logic “0”); a resistor must be connected between pin “A”

and a fixed supply voltage. The output current can be

programmed to any desired value within the specified

range. The FAN5608DHMPX is available in a 4x4mm

12-lead MLP package. A single external resistor sets the

current and turns the device ON and OFF.

Applications

Cell phones

Handheld computers

PDAs, DSCs, MP3 players

Keyboard backlights

LED displays

Ordering Information

Part Number

Pb-Free

Schottky Diode

Package

Packing Method

FAN5608DHMPX

Yes

Internal

MLP-12 4x4mm

Tape and Reel

FAN5608 Rev. 1.0.5 • 8/8/06

www.fairchildsemi.com

Block Diagram

Figure 1. Block Diagram

Pin Configuration

TOP-VIEW

NC V_OUTINDB

12

11

10

1

2

3

9

8

7

GND

INDA

CH2

B2

CH1

B1

4

5

6

A1 V_INA2

4x4mm 12-Lead MLP(QUAD)

(Internal Schottky Diode)

FAN5608DHMPX

Figure 2. FAN5608M MLP package

FAN5608 Rev. 1.0.5 • 8/8/06

www.fairchildsemi.com

2

Pin Definitions

Pin #

Name

Description

1

GND

CH1

B1

Ground

2

First LED Cathode

3

DAC B1

4

A1

DAC A1

5

VIN

A2

Input Voltage

6

DAC A2

7

B2

DAC B2

8

CH2

INDA

INDB

VOUT

NC

Second LED Cathode

9

SD Anode. INDA and INDB must be connected together externally on the PCB.

Inductor. INDA and INDB must be connected together externally on the PCB.

Output LEDs Anode

10

11

12

No Connection

Absolute Maximum Ratings

The “Absolute Maximum Ratings” are those values beyond which the safety of the device cannot be guaranteed. The

device should not be operated at these limits. The parametric values defined in the Electrical Characteristics tables

are not guaranteed at the absolute maximum ratings. The “Recommended Operating Conditions” table defines the

conditions for actual device operation.

Parameter

Min.

Max.

Units

V_INto GND

-0.3

6.5

35

V

V_OUTto GND

CH1,CH2 Voltage to GND

All Other Pins

25

V

-0.3

-20

-65

V_IN+0.3

150

V

Junction Temperature (T_J)

Storage Temperature

Lead Soldering Temperature, 10 seconds

°C

150

300

HBM

CDM

1.5

2

Electrostatic Discharge Protection ^(1,2)

kV

Notes:

1. Using Mil Std. 883E, method 3015.7 (Human Body Model) and EIA/JESD22C101-A (Charge Device Model).

2. Avoid positive polarity ESD stress at the cathode of the internal Schottky diode (Schottky diode cathode <1.5kV).

Recommended Operating Conditions

Parameter

Conditions

Min.

Typ.

Max.

Units

Supply Voltage V_IN

P_OUT<0.6W, 2 channels evenly loaded

2.7

V_IN

-40

5.5

24

85

V

Output Voltage Range

Ambient Temperature (T_A)

25

°C

FAN5608 Rev. 1.0.5 • 8/8/06

www.fairchildsemi.com

3

Typical Application

Digital Brightness Control

C_IN

L = 4.7µH

2.7V to 5.5V

INDA

V_OUT

INDB

V_IN

A1

V_OUT

4.7µF

GND

CH2

CH1

DAC Input For CH1

DAC Input For CH2

FAN5608DHMPX

B1

A2

B2

NC

Figure 3. FAN5608 Digital Brightness Circuit

Analog Brightness Control

C

IN

L = 4.7µH

2.7V to 5.5V

INDA

INDB

V

OUT

V

OUT

IN

V

4.7µF

EXTERNAL

A1

GND

CH2

CH1

FAN5608DHMPX

A2

B1

B2

NC

Figure 4. FAN5608 Analog Brightness Circuit

FAN5608 Rev. 1.0.5 • 8/8/06

www.fairchildsemi.com

4

Electrical Specifications

Recommended operating conditions and component values are per the Figure 18 test circuit. Typical values are at

25°C and VIN=3.6V. Boldface indicates specifications over ambient operating temperature (-40°C to +85°C).

Parameter

Conditions

Min.

Typ.

Max.

Units

Supply current in OFF mode

LED current accuracy

Current matching⁽³⁾

A input LOW, B input LOW

A input HIGH, B input HIGH

0.1

20

µA

mA

%

1

22

3

18

Switching frequency

500

1.2

KHz

V

Internal reference voltage, V_A

Current multiplication ratio

Power efficiency (AVG)⁽⁴⁾

Analog Control Mode

850

1000

80

1150

V_IN> 3V

%

V

HIGH

LOW

V_IN-0.7

0

V_IN

0.6

Digital Control Mode

Analog Control Mode

Digital Control Mode

Input A1, A2 threshold

1.2

50

HIGH

LOW

0.6 x V_IN

0

V_IN

0.3 x V_IN

80

Input B1, B2 threshold

Input A1, A2 current

V

V_A= V_IN

V_A=0

µA

0.1

Input B1, B2 current

Digital Control Mode

0.1

µA

Notes:

3. Current matching is the absolute value of the difference in current of the two LEDs channels, divided by the

average current in the two channels.

4. Power efficiency is the ratio between the electrical power to the LEDs and the total power consumed from the

input power supply. Although this definition leads to a lower value than the boost converter efficiency, it more

accurately reflects the system performance in an application.

Circuit Description

LED Brightness Control

When power is applied to the V_INpin, the system is

enabled, the bandgap reference acquires its nominal

voltage (1.2V), and the soft-start cycle begins. Once

“power good” is achieved (when 0.5mA voltage flows

through the LEDs), the soft-start cycle stops, and the

boost voltage increases to generate the current selected

by the input control pins (A1, A2, B1, B2).

The control inputs are A1 and B1 for CH1 and A2 and

B2 for CH2. B1 and B2 are digital inputs that require

LOW (GND) and HIGH V_INcontrol signals. In analog

mode, A1 and A2 are connected to an external stable

voltage source via an external resistor, and B1 and B2

inputs are connected to ground. The current flowing

through the resistor is scaled by

approximately 1000.

a

factor of

If CH1 is not selected, the CH1 output pin is HIGH, its

output measurement is approximately equal to V_OUT

,

LED dimming can be controlled with static or dynamic

inputs from CH1 and CH2. CH1 and CH2 outputs are

driven directly by A1, B1 and A2, B2 inputs, respectively.

Either channel can be configured as analog or digital.

Inputs A1 and A2 are analog inputs that can be

connected to an external regulated voltage source,

which can be calculated by:

and its LEDs are OFF. The FAN5608 provides tightly

regulated output currents for the selected LED’s

channel. An internal feedback loop determines which

LED string requires the highest output voltage to sustain

the pre-set current. It also adjusts the boost regulator

based on CH1 and CH2 feedback voltage and A1, A2,

B1, B2 input settings. System efficiency decreases if the

channels’ strings of LEDs have different forward voltage.

EQ 1

If one channel is used, the other channel should be

disabled by connecting the corresponding DAC inputs to

logic LOW. If the external output capacitor V_OUTis

shorted to GND, the internal Schottky diode can be

damaged, a condition which should be avoided.

where current multiplication ratio is according to the

Electrical Specifications table.

Inputs B1 and B2 are digital inputs and can only be set

by external logic of “0” (LOW) or “1” (HIGH).

FAN5608 Rev. 1.0.5 • 8/8/06

www.fairchildsemi.com

5

Digital Static Control

PWM Control in Digital Dynamic Mode

The FAN5608’s digital decoder allows selection of the

following modes of operation: OFF, 5mA, 10mA, and

20mA per channel.

In Digital Dynamic Mode, if inputs A1 and/or A2 are

externally driven by an open-drain output, the pull-up

resistance should be less than 10kΩ to ensure less than

0.7V dropout; VA> (V –0.7V), as required for HIGH logic

level.

IN

A

B

0

1

0

1

The logic level HIGH (VH) and logic level LOW (VL) of

the PWM signal should be:

I_LED

OFF

5mA

10mA

20mA

(V_IN– 0.7V) < VH < V_IN

and

EQ 3

Analog Static Control

In Analog Mode, B1 and B2 inputs should be connected

to GND or “0” logic. A1 and A2 control the LED current

through an external resistor (R), as shown in Figure 4, or

an external voltage (V_EXT) input.

0 < VL < 0.6V.

EQ 4

The frequency of the PWM signal should be within the

50Hz to 1kHz range, by default, or 30kHz at any input if

the other input is kept HIGH.

The I_LEDvalue can be calculated using the formula or

the graph below:

PWM Control in Analog Dynamic Mode

In Analog Dynamic Mode, the logic level HIGH (VH) and

logic level LOW (VL) of the PWM signal should be:

EQ 2

where 1.2V < V_EXT≤ R(kΩ) x 0.020(mA) + 1.2V and the

current multiplication ratio is according to the Electrical

Specifications table. The R value should be in the (10kΩ

to 50kΩ) range.

VH = V_EXTand 0 < VL < 0.6V.

EQ 5

The frequency of the PWM signal should be in the range

from 50Hz to 1kHz. The V_EXTamplitude sets the

maximum LED current, while the duty cycle of the PWM

signal sets the average current between 0mA and I_LED

maximum.

25

R=10k

20

Open-Circuit Protection

The FAN5608 has an internal over-voltage protection

mechanism that prevents damage to the IC in a no-load

condition. If CH1 and/or CH2 LEDs are enabled in an

open-circuit condition, FAN5608 automatically sets the

duty cycle to 25%. The output voltage can reach as high

as 50V at maximum V_IN(5.5V). Depending on the

capacitor’s rating, the output capacitor may be at risk in

this condition.

15

10

R=50k

5

Shutdown Mode

0

Each channel can be independently disabled by

applying LOW logic level voltage to the appropriate A

and B inputs. When both channels are disabled, the

FAN5608 enters shutdown mode and the supply current

is reduced to less than 1μA.

1.0

1.25

1.5

V

1.75

(V)

2

2.25

EXT

Figure 7. Analog Control

FAN5608 Rev. 1.0.5 • 8/8/06

www.fairchildsemi.com

6

PWM Control

Figure 8. A is PWM controlled; B is LOW; I_LED(average) – s x 5mA, where s is the duty cycle⁽⁵⁾

A Input

B Input (PWM)

30%

Duty Cycle

70%

Duty Cycle

1KHz

I

OFF

0mA

LED

Figure 9. A is HIGH and B is PWM controlled; I_LED(average) – s x 15mA +5mA, where s is the duty cycle⁽⁶⁾

A Input (PWM)

30%

Duty Cycle

70%

Duty Cycle

1KHz

B Input (PWM)

30%

Duty Cycle

70%

Duty Cycle

1KHz

I

0mA

OFF

LED

Figure 10. A and B are PWM controlled; I_LED(average) – s x 20mA, where s is the duty cycle⁽⁷⁾

Notes:

5. Proportionally select the duty cycle to achieve a typical LED current from 1mA to 4mA.

6. Maximum PWM frequency can be 30KHz.

7. Proportionally select the duty cycle to achieve a typical LED current from 1mA to 19mA.

www.fairchildsemi.com

FAN5608 Rev. 1.0.5 • 8/8/06

7

Typical Characteristics

T_A=25C, V_BAT= 3.6V, unless otherwise specified.

Figure 11. Peak power efficiency

Startup Response

Figure 12. PWM Dimming

V_IN=3.6V, L=6.8uH, C_OUT=4.7uF, 3-LEDs/CH

Time 200µS/Div

Figure 13. Startup Response

Design and Component Selection Guidelines

on the maximum output power (P_OUT) and the minimum

input voltage (V_IN):

Inductor Selection

The inductor is one of the main components required by

the boost converter to store energy. The amount of

energy stored in the inductor and transferred to the load

is controlled by the regulator, using pulse-frequency

modulation (PFM) and pulse-skipping techniques. In most

cases, the FAN5608 operates in discontinuous conduction

mode, resulting in higher inductor current ripple.

(V_IN)²×T

P_OUT

L ≤

EQ 6

where units of L, V_IN, and P_OUTare in μH, Volt, and Watt,

respectively and T = 0.4μs is a factor depending upon

the FAN5608 internal architecture. The above

relationship is applicable up to P_OUT= 0.8W and

L ≥ 2.2μH . At lower inductor values, the efficiency

To ensure proper operation of the current regulator over

the entire range of conditions, select the inductor based

FAN5608 Rev. 1.0.5 • 8/8/06

www.fairchildsemi.com

8

decreases due to the resistive loss in the switching

power FET. Using L = 3.3μΗ and increasing the load to

12 LED x 20mA (P_OUT= 800mW) requires V_IN> 3.5V to

maintain a constant 20mA current through LEDs. An

inductance L = 4.7μH ensures proper operation for 2 x 4

white LEDs with regulated 20mA current if V_IN> 2.7V.

The current feeding the string of LEDs is the sum of the

currents programmed for each channel in digital or

analog mode. Using all four inputs in digital mode, the

LED current can be programmed within the 0 to 40mA

range, according to the following table:

For any lighter load or higher V_IN, the inductance may be

increased to improve the system efficiency. Application

examples are given in Figures 16 - 25.

The peak current in the inductor depends on the

maximum battery voltage and the inductance, according

to the equation:

1.4μS ×V_IN

max

I_pk

=

EQ 7

L

which gives the maximum rated current for the inductor.

For L =4.7μH and V_IN= 4.2V, the inductor saturation

current should be at least 1A.

Capacitors Selection

Low ESR capacitors should be used to minimize the

input and output ripple voltage. Use of a C_IN

>

4.7μF/6.3V and C_OUT= 4.7μF/25V type X5R/X7R multi-

layer ceramic capacitor is recommended.

A larger value input capacitor placed as close as

possible to FAN5608 may be needed to reduce the input

voltage ripple in noise-sensitive applications. An

additional LC filter between the battery and the

FAN5608 input can help reduce the battery ripple to the

level required by a particular application.

Driving Two Independent Strings of LEDs

For best efficiency, the two strings of LEDs driven by the

FAN5608 should have close forward voltages. This

recommendation is met when the same number and

type of LEDs are serially connected in each channel. If

the application requires the two channels be significantly

unbalanced, an external resistor may be added in series

with the shorter string of LEDs to reduce the voltage

difference between the two channels and enhance

performance. The maximum differential LEDs connected

in series to CH1 and CH2 is not recommended to

exceed three LEDs.

Driving Higher Current LEDs

To increase the LED current range to 50mA, the CH1

and CH2 outputs may be connected, as shown below:

C

IN

L = 4.7µH

INDA

GND

INDB

2.7V to 5.5V

4.7µF

A

B

1

Specific Layout Recommendations

CH1

CH2

DAC Inputs

The FAN5608 is available in a dual Die Attach Pad

(DAP) package. One DAP is connected to GND and

another to V_OUT, making it unnecessary to provide any

external connection to the DAPs. Since the internal

power dissipation is low, the 4x4mm MLP package is

capable of dissipating maximum power without requiring

an extra copper field on the printed circuit board. When

viewing the bottom of the dual-DAP device package, two

electrically isolated exposed metal islands are visible.

The two IND pins should be connected externally.

Depending on the application noise sensitivity, an

external filter may be required between the battery and

the IC input.

A

B

2

Figure 14. Digital Brightness Control

C

IN

L = 4.7µH

INDA

GND

INDB

2.7V to 5.5V

4.7µF

V

IN

V

EXT

A

1

2

CH1

CH2

Figure 15. Analog Brightness Control

FAN5608 Rev. 1.0.5 • 8/8/06

www.fairchildsemi.com

9

FAN5608 Efficiency Curves

L = 6.9µH

2.7V to 5.5V

INDA

INDB

V

OUT

V

OUT

IN

4.7µF

A1

GND

CH2

CH1

DAC Input for CH1

FAN5608DHMPX

A2

B1

B2

DAC Input for CH2

NC

Figure 16. FAN5608 with four LEDs

Figure 17. FAN5608 efficiency with four LEDs

L = 6.8µH

2.7V to 5.5V

INDA

INDB

V

OUT

V

OUT

IN

4.7µF

A1

GND

CH2

CH1

DAC Input for CH1

FAN5608DHMPX

A2

B1

B2

DAC Input for CH2

NC

Figure 18. FAN5608 with six LEDs

Figure 19. FAN5608 efficiency with six LEDs

L = 4.7µH

2.7V to 5.5V

INDA

V_OUT

INDB

V_IN

V_OUT

4.7µF

A1

GND

CH2

CH1

DAC Input for CH1

FAN5608DHMPX

A2

B1

B2

DAC Input for CH2

NC

Figure 20. FAN5608 with eight LEDs

Figure 21. FAN5608 efficiency with eight LEDs

FAN5608 Rev. 1.0.5 • 8/8/06

www.fairchildsemi.com

10

L = 3.3µH

2.7V to 5.5V

INDA

INDB

V

OUT

V

OUT

IN

4.7µF

A1

GND

CH2

CH1

DAC Input for CH1

FAN5608DHMPX

A2

B1

B2

DAC Input for CH2

NC

Figure 22. FAN5608 with ten LEDs

Figure 23. FAN5608 efficiency with ten LEDs

L = 2.7µH

2.7V to 5.5V

INDA

INDB

V

OUT

V

OUT

IN

4.7µF

A1

GND

CH2

CH1

DAC Input for CH1

FAN5608DHMPX

A2

B1

B2

DAC Input for CH2

NC

Figure 24. FAN5608 with twelve LEDs

Figure 25. FAN5608 efficiency with twelve LEDs

FAN5608 Rev. 1.0.5 • 8/8/06

www.fairchildsemi.com

11

Dimensional Outline Drawings

Dimensions are in millimeters unless otherwise noted.

Figure 26. 4x4mm 12-Lead MLP

FAN5608 Rev. 1.0.5 • 8/8/06

www.fairchildsemi.com

12

TRADEMARKS

The following are registered and unregistered trademarks Fairchild Semiconductor owns or is authorized to use and is not intended to be an

exhaustive list of all such trademarks.

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ImpliedDisconnect™

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DISCLAIMER

FAIRCHILD SEMICONDUCTOR RESERVES THE RIGHT TO MAKE CHANGES WITHOUT FURTHER NOTICE TO ANY PRODUCTS

HEREIN TO IMPROVE RELIABILITY, FUNCTION OR DESIGN. FAIRCHILD DOES NOT ASSUME ANY LIABILITY ARISING OUT OF THE

APPLICATION OR USE OF ANY PRODUCT OR CIRCUIT DESCRIBED HEREIN; NEITHER DOES IT CONVEY ANY LICENSE UNDER

ITS PATENT RIGHTS, NOR THE RIGHTS OF OTHERS. THESE SPECIFICATIONS DO NOT EXPAND THE TERMS OF FAIRCHILD’S

WORLDWIDE TERMS AND CONDITIONS, SPECIFICALLY THE WARRANTY THEREIN, WHICH COVERS THESE PRODUCTS.

LIFE SUPPORT POLICY

FAIRCHILD’S PRODUCTS ARE NOT AUTHORIZED FOR USE AS CRITICAL COMPONENTS IN LIFE SUPPORT DEVICES OR

SYSTEMS WITHOUT THE EXPRESS WRITTEN APPROVAL OF FAIRCHILD SEMICONDUCTOR CORPORATION.

As used herein:

1. Life support devices or systems are devices or systems 2. A critical component in any component of a life support,

which, (a) are intended for surgical implant into the body or

(b) support or sustain life, and (c) whose failure to perform

when properly used in accordance with instructions for use

provided in the labeling, can be reasonably expected to

result in a significant injury of the user.

device, or system whose failure to perform can be

reasonably expected to cause the failure of the life

support device or system, or to affect its safety or

effectiveness.

PRODUCT STATUS DEFINITIONS

Definition of Terms

Datasheet Identification

Product Status

Definition

Advance Information

Formative or In

Design

This datasheet contains the design specifications for product

development. Specifications may change in any manner without

notice.

Preliminary

First Production

Full Production

Not In Production

This datasheet contains preliminary data; supplementary data will

be published at a later date. Fairchild Semiconductor reserves the

right to make changes at any time without notice to improve design.

No Identification Needed

Obsolete

This datasheet contains final specifications. Fairchild

Semiconductor reserves the right to make changes at any time

without notice to improve design.

This datasheet contains specifications on a product that has been

discontinued by Fairchild Semiconductor. The datasheet is printed

for reference information only.

Rev. I20

FAN5608 Rev. 1.0.5 • 8/8/06

www.fairchildsemi.com

13


型号：	FAN5608_06
厂家：	FAIRCHILD SEMICONDUCTOR
描述：	Serial / Parallel LED Driver with Current-Regulated, Step-Up DC/DC Converter 串行/并行LED驱动电流稳压，升压型DC / DC转换器转换器驱动
文件：	总13页 (文件大小：366K)
中文：	中文翻译
下载：	下载PDF数据表文档文件

FAN5608_06 [FAIRCHILD]

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