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FAN5606
Serial LED Driver with Current-Regulated, Step-Up DC/DC Converter
Features
* * * * * * * * * * * * * * * Drives Up to Six LEDs in Series Pulse Skip PWM Mode of Operation of the Boost Circuit Up to 90% Peak Efficiency No External Schottky Diode Required Up to 25mA Output Built-in DAC for Digital Brightness Control LED's Current Can be Duty-Cycle-Modulated Digital, Analog, and PWM Brightness Control 2.7V to 5.5V Input Voltage Range 0.5MHz Operating Frequency (8MHz internal clock) Soft Start Low Shutdown Current: ICC < 1A LED Short Circuit Protection Minimal External Components Needed Available in an 8-lead MLP Package
Description
The FAN5606 LED driver generates regulated output currents from a battery with input voltage varying between 2.7V to 5V. An internal NMOS switch drives an external inductor, and a Schottky diode delivers the inductor's stored energy to the load. Soft start circuitry prevents excessive current drawn from the supply during power on. Any number of LEDs can be connected in series as long as the summed forward voltages do not lead to exceeding the specified operating output voltage range. In the FAN5606 device, the internal two-bit D/A converters provide programmability of the output channel current. Analog programming of the output current is also possible in the FAN5606. To do this, ground the "B" pin and connect a resistor between the "A" pin and a fixed supply voltage. The output current can then be programmed to any desired value within its specified range. The analog version uses a single external resistor to set the current, and to turn the device ON and OFF. The device is available in an 8-lead MLP package.
Applications
* * * * * Cell Phones Handheld Computers PDAs, DSCs, MP3 Players Keyboard Backlights LED Display
Typical Applications
Analog Brightness Control
VOUT 2.7V to 5.5V L = 6.8H
IND VOUT GND IN
Digital Brightness Control
VOUT 2.7V to 5.5V L = 6.8H
IND GND IN
4.7F
4.7F
CIN
VIN
CIN
VIN
FAN5606
FAN5606
CAT
CAT
VExternal
R
A
B
DAC Inputs
A
B
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FAN5606
PRODUCT SPECIFICATION
Pin Assignment
A B CAT IND VIN NC GND VOUT
1 2 3 4
8 7 6 5
FAN5606 8-Lead 3x3mm MLP
Pin Descriptions
Pin No. 1 2 3 4 5 6 7 8 Pin Name A B CAT IND VOUT GND NC VIN Pin Function Description DAC A Input DAC B Input LED Cathode Inductor Output LED's Anode Ground No Connection Input Voltage
Definition of Terms
Output Current Accuracy: reflects the difference between the measured value of the output current (LED) and programmed value of this current. ( I OUT measured - I OUT programmed ) x 100 Output Current Accuracy (%) = -----------------------------------------------------------------------------------------------------------I OUT programmed
Efficiency: is expressed as a ratio between the electrical power into the LEDs and the total power consumed from the input power supply. ( V LED x I LED ) x 100 Efficiency (%) = -------------------------------------------------------V IN x I IN Although this definition leads to a lower value than the boost converter efficiency, it more accurately reflects better system performance, from the user's point-of-view.
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REV. 1.0.3 1/7/05
PRODUCT SPECIFICATION
FAN5606
Absolute Maximum Ratings
Parameter VIN, A, B Voltage to GND VOUT, CAT Voltage to GND Any LED Short Circuit Duration (Anode to Cathode) Lead Soldering Temperature (10 seconds) Thermal Resistance jc Operating Junction Temperature Range Storage Temperature Range Electrostatic Discharge (ESD) Protection (Note 1, 2) HBM CDM -55 4 1 8 150 150 Min -0.3 -0.3 Typ Max 6.5 24 Indefinite 300 C C/W C C kV Unit V V
Electrical Characteristics
VIN =2.7V to 5.5V, TA = 25C, unless otherwise noted.
Parameter Conditions Min. Typ. Max. Units
Output Current Accuracy Efficiency (AVG) Switching Frequency Multiplication Ratio (Note 3) Supply Current in OFF mode Input A Threshold Digital Mode Analog Mode Input B Threshold Digital Mode
A = HIGH, B = HIGH VIN > 3.0V
0.9 x I NOM INOM = 20 1.1 x I NOM 80 0.5 850 1000 0.1 VIN-0.7 0 1.2 0.6 x V IN 0 VIN 0.6 VIN 0.3 x V IN 1150
mA % MHz
VA = VB = 0V High Low High Low
A
V
V
Recommended Operating Conditions
Parameter Input Voltage Range Operating Ambient Temperature Range Output Voltage Range Min 2.7 -40 VIN 25 Typ Max 5.5 85 18 Unit V C V
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. 3. Multiplication Ratio is ILED /I INPUT A .
REV. 1.0.3 1/7/05
3
FAN5606
PRODUCT SPECIFICATION
Block Diagram
V OUT
V
IN
OSC
DBB
COIL DRIVER
IND
START-UP AMPLIFIER B A DAC
LINEAR REGULA TOR
CAT
BG
REF
POWER GOOD
GND
Circuit Description
When the input voltage is connected to VIN pin, the system is turned on, the bandgap reference acquires its nominal voltage and the soft-start cycle begins. Once "power good" is achieved (0.5mA in the diodes), the soft-start cycle stops and the boost voltage increases to generate the desired current selected by the input control pins. The FAN5606 DC/DC converter automatically adjusts its internal duty cycle to achieve high efficiency. If the output external capacitor is shorted, the Schottky diode can be damaged, therefore such a condition should be avoided.
Digital Control The FAN5606's digital decoder allows selection of the following modes of operation: OFF, 5mA, 10mA, 20mA per branch. A B ILED 0 0 OFF 1 0 5mA 0 1 10mA 1 1 20mA
LED Brightness Control
The inputs A and B can be digitally controlled LOW (GND) and HIGH (VCC) signals. In analog mode, A input is connected to an external stable voltage source via an external resistor and B input is connected to ground. The current flowing through the resistor is scaled by a factor of approximately 1000. 4
Analog Control with PWM In analog control mode, the LED current can go up to 25mA. Input A is used to control the LED currents. Input B should be connected to GND (logic level "0"). An external resistor (R) is connected from A to a stable voltage source (VEXTERNAL) to control the LED current, ILED. The ILED is given by the formula or the graph below: V External - V Ref I LED = ----------------------------------------- x Multiplication Ratio R
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PRODUCT SPECIFICATION
FAN5606
Where V Ref = 1.22V
25 R=10Kohm 20 I LED (mA) 15 10 5 0 1.25 R=100kohm
Pulse-Width-Modulation (PWM) Control A variable duty cycle () can modulate any DAC input. Care should be taken not to use a too low frequency, otherwise a flickering effect may occur. The minimum range is 100Hz to 1KHz. For a maximum range of LED current, both A and B inputs can be modulated at the same time.
Open Circuit Protection
A built-in over voltage protection circuit prevents the device from being damaged when it is powered up with no load. This circuit reduces the boost converter duty cycle, to a minimum thus limiting the output voltage to a safe value when no load condition is detected. However, the FAN5606 can be damaged when a full load (Six LEDs driven by 20mA) is suddenly disconnected from VOUT. To protect the FAN5606 against this unlikely event, an external 24 V Zener diode can be connected between VOUT and GND.
1.5
1.75
2
2.25
2.5
2.75
3
3.25
3.5
VExternal (V)
If the analog input A is driven in digital mode by an open drain output, it is important to choose the appropriate value of the pull-up resistor. Its resistance should be low enough to ensure less than 0.7V dropout, hence VA > (VIN-0.7V), as required for HIGH logic level: 700mV Rpull-up < ----------------- = 11k 60A
Shutdown Mode
The device can be disabled by applying LOW logic level voltage to the A and B inputs. In Shutdown mode the supply current is reduced to less than 1A.
PWM Control
1. A is PWM Controlled, B is Low. ILED (Average) = x 5mA, where is Duty Cycle. (Note 4)
A Input (PWM)
ss
30% Duty Cycle 1KHz
ss
70% Duty Cycle 1KHz
ss
B Input (0)
ILED (Average) = 0.7 x 5mA = 3.5mA ILED (Average) = 0.3 x 5mA = 1.5mA ILED 0mA
ss
OFF
2. A is High and B is PWM. ILED (Average) = 5mA + x 15mA, where is Duty Cycle.(Note 5, 6)
A Input
ss
B Input (PWM)
ss
30% Duty Cycle 1KHz
ss
70% Duty Cycle 1KHz
ss
ILED (Average) = 0.7 x 20mA + 0.3 x 5mA = 15.5mA ILED (Average) = 0.3 x 20mA + 0.7 x 5mA = 9.5mA
ss
ILED
0mA
OFF
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FAN5606
PRODUCT SPECIFICATION
PWM Control (Continued)
3. A and B are PWM. ILED (Average) = x 20mA, where is Duty Cycle.
A Input (PWM)
ss
30% Duty Cycle 1KHz
ss
70% Duty Cycle 1KHz
ss
B Input (PWM)
ss
30% Duty Cycle 1KHz
ss
70% Duty Cycle 1KHz
ss
ILED (Average) = 0.7 x 20mA = 14mA
ILED (Average) = 0.3 x 20mA = 6mA
LED CURRENT
0mA
ss
OFF
Notes: 4. Proportionally select the duty cycle to achieve a typical LED current between 1mA to 4mA. 5. Maximum PWM frequency can be up to 30KHz. 6. Proportionally select the duty cycle to achieve a typical LED current between 1mA and 19mA.
Applications Information
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 PWM and pulse skipping techniques. In most cases, the FAN5606 operates the inductor in discontinuous conduction mode. To ensure proper operation of the current regulator over the entire range of conditions, the inductor should be selected based on the maximum required power (POUT) and the minimum input voltage (VIN). ( V IN ) x F L < -------------------------P OUT where units of L, VIN, and POUT are in H, Volt, and Watt, respectively and F = 0.4 is a factor depending upon the FAN5606 architecture.
2
The above relation is applicable up to POUT = 0.6W and L = 4.3 , or greater. The peak current in the inductor is: T ON_Max x V IN_Max I = ------------------------------------------------L where TON_Max = 1.25S. The recommended inductor for driving upto 6 LEDs, type QTLP670CiW is L = 6.8H rated at minimum 0.5A. Low ESR capacitors should be used to minimize the input and output ripple voltage. Use of CIN = 4.7F/6.3V and COUT = 4.7F/25V type X5R/X7R multi layer ceramic capacitor are recommended. A larger value input capacitor placed as close as possible to FAN5606 may be needed to reduce the input voltage ripple in noise sensitive applications. An additional LC filter between the battery and the FAN5606 input can help to further reduces the battery ripple to the level required by a particular application.
6
REV. 1.0.3 1/7/05
PRODUCT SPECIFICATION
FAN5606
Typical Performance Characteristics
TA = 25 C, CIN = 47F, COUT = 4.7F, L = 6.8H, unless otherwise noted.
Regulated LED Current vs Input Voltage
10.5 5.4 20
Efficiency vs Input Voltage
0.95
2 x 20mA Load, L = 22H
0.90
LED Current (mA) Scale1
LED Current (mA) Scale2
LED Current (mA) Scale3
Efficiency (%)
5.2 5.0 4.8 4.6 2.5 3.0 3.5 A=1, B=0 Scale1 A=0, B=1 Scale2 A=1, B=1 Scale3
10.0
19 18 17 16 15
0.85 0.80 0.75 0.70 0.65 0.60 2.5 3.0 3.5 4.0 4.5 5.0 5.5
9.5
9.0
4 x 20mA Load, L = 6.8H
4.0
4.5
5.0
8.5 5.5
Input Voltage (V)
Input Voltage (V)
Shutdown Current vs Input Voltage
0.065
Shutdown Current (A)
0.060 0.055 0.050 0.045 0.040 0.035 2.5 3.0 3.5 4.0 4.5 5.0 5.5
Input Voltage (V)
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FAN5606
PRODUCT SPECIFICATION
Mechanical Dimensions
3x3mm 8-Lead MLP (Internal Schottky Diode)
2.54 GND 0.15 C 2X 3.0 A 8 B 1.37 1.27 5 0.76 VOUT
1.99 1.40 3.0 (0.65) 1 0.15 C 2X 0.65 TYP 4
1.18
3.30
0.42 MAX
TOP VIEW
0.8 MAX 0.10 C (0.20) 0.08 C 0.05 0.00 SEATING PLANE C
RECOMMENDED LAND PATTERN
SIDE VIEW
2.54 MAX 1.37 1.26 4 1
PIN #1 IDENT
0.76
0.45 0.43 1.40 MAX 1.18
8 0.65 1.95
5
0.25~0.35 0.10 M C A B 0.05 M
BOTTOM VIEW
NOTES: A. CONFORMS TO JEDEC REGISTRATION MO-229, VARIATION VEEC, DATED 11/2001 B. DIMENSIONS ARE IN MILLIMETERS. C. DIMENSIONS AND TOLERANCES PER ASME Y14.5M, 1994
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REV. 1.0.3 1/7/05
PRODUCT SPECIFICATION
FAN5606
Ordering Information
Product Number FAN5606 Package Type 8-Lead 3x3mm MLP Order Code FAN5606DMPX
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. 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 THE PRESIDENT OF FAIRCHILD SEMICONDUCTOR CORPORATION. As used herein: 1. Life support devices or systems are devices or systems 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. www.fairchildsemi.com
REV. 1.0.3 5/12/04 2005 Fairchild Semiconductor Corporation
2. A critical component in any component of a life support 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.

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