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FAN5617 -- High-Efficiency, Constant-Current LED Driver with TinyWireTM Brightness Control
April 2007
FAN5617
High-Efficiency, Constant-Current LED Driver with TinyWireTM Brightness Control
Features
Three-Channel Parallel LED Driver for a Large Range of Forward Voltages TinyWireTM Single-Wire Digital Brightness Control 32 Static Brightness Levels with 5-Bit Internal DAC Adaptive VOUT Adjustment to the Highest Diode Forward Voltage Matched LED Currents; Matched or Unmatched LEDs Built-in Charge Pump with Three Modes of Operation: 1x (linear), 1.5x, and 2x Up to 90% Efficiency Low EMI, Low Ripple Up to 90mA Total Output Current Drives up to Three LEDs at 30mA Each External Resistor Sets Maximum (100%) LED Current 2.7V to 5.5V Input Voltage Range 1MHz Operating Frequency Shutdown Isolates Output from Input, Typically <1A Protections: Short-Circuit; Soft-Start Limits Inrush Current Minimal External Components Required 3x3mm 16-Lead MLP Package
Description
The FAN5617 is a low-ripple, low-EMI, high-efficiency, constant-current LED driver that drives three LEDs in parallel. The LED brightness control is programmable through Fairchild's proprietary single-wire digital interface, TinyWireTM. The charge pump DC/DC converter operates in three modes: 1X, 1.5X, and 2X over the entire input voltage range of 2.7V to 5.5V. The adaptive nature of the built-in charge pump eliminates the need for LED pre-selection (matching) and delivers high output efficiency. FAN5617 is capable of driving up to 90mA total output current, 30mA per channel. The driver's built-in, proprietary auto-sense circuit ensures the same efficiency regardless of the number of LEDs connected. When the input voltage is insufficient to sustain the LEDs programmable current level, the FAN5617 reconfigures itself to operate as a linear regulator and the charge pump circuit turns off. The FAN5617 features Fairchild's TinyWireTM singlewire digital interface for LED brightness control. The built-in 5-bit DAC provides selection of 32 dimming levels, where each level is a percentage of the maximum LED current set by the external resistor, RSET. The FAN5617 includes shutdown, short-circuit, and thermal protection circuitry. Minimal external components are required: two bucket capacitors (2F and 1F), a 4.7F input capacitor, and a 1F output capacitor are needed for proper operation. The FAN5617 is available in a 3x3mm, 16-lead, molded leadless package (MLP).
Applications
Portable Handheld Backlight PDAs, DVD players, Pagers, Camcorder Backlights Portable Medical Diagnostic Equipments Display MP3 Player Displays Digital Still Camera Backlight
Ordering Information
Part Number
FAN5617MPX
Pb-Free
Yes
Operating Temperature Range
0C to 85C
Package
MLP-16 3x3mm
Packing Method
Tape and Reel
TinyWireTM is a trademark of Fairchild Semiconductor Corporation.
(c) 2006 Fairchild Semiconductor Corporation FAN5617 Rev. 1.0.1
www.fairchildsemi.com
FAN5617 -- High-Efficiency, Constant-Current LED Driver with TinyWireTM Brightness Control
Application Diagram
EN DATA RSET 16 15 14 13 1 2 3 4 5 6 7 8 COUT VOUT P1 = GND 12 11 10 9 CAP1 CAP2 CIN VIN
CIN CAP1, CAP2 COUT RSET
4.7F 0.1F 1F 15K
Figure 1. Typical Application
Pin Configuration
DATA GND
14 16 15
RSET N/C N/C LED-
1 2
VIN
13 12 11
EN
CAP2- CAP1- CAP1+ CAP2+
P1 = GND
3 4 10 9
5
6
7
8
LED-
LED-
Figure 2. Top View 3x3mm MLP Package
Pin Definitions
Pin
1 2,3 4-6 7 8 9 10 11 12 13 14 15 16
Name
RSET N/C LED- P1, PGND VOUT CAP2+ CAP1+ CAP1- CAP2- VIN GND EN DATA
Description
Current set resistor. A resistor from this pin to GND sets the maximum LED current. No internal connection. LED cathode drive. Power Ground for the IC. Solder to PCB ground plane. Regulated Output Voltage. Connect to output capacitor and anodes of all LEDs. Bucket Capacitor 2. Connect this pin to the positive terminal of the bucket capacitor Bucket Capacitor 1. Connect this pin to the positive terminal of the bucket capacitor Bucket Capacitor 1. Connect this pin to the negative terminal of the bucket capacitor Bucket Capacitor 2. Connect this pin to the negative terminal of the bucket capacitor Supply Input Voltage. Ground. All signals are referenced to this point. Solder to PCB ground plane. Enable. Enables the IC when high and disables at HIGH-to-LOW transition. The TinyWire control overrides the state of the EN pin if a command is received. DATA input for TinyWire brightness control. This pin has a 33k internal pull-up resistor to VIN.
(c) 2006 Fairchild Semiconductor Corporation FAN5617 Rev. 1.0.1
PGND
VOUT
www.fairchildsemi.com
FAN5617 -- High-Efficiency, Constant-Current LED Driver with TinyWireTM Brightness Control
Absolute Maximum Ratings
Stresses exceeding the absolute maximum ratings may damage the device. The device may not function or be operable above the recommended operating conditions and stressing the parts to these levels is not recommended. In addition, extended exposure to stresses above the recommended operating conditions may affect device reliability. The absolute maximum ratings are stress ratings only.
Parameter
VIN, VOUT, EN, DATA, GND Voltage on All Other Pins CAP+, CAP- to GND Thermal Resistance - Junction to Tab (JC) Lead Soldering Temperature (10 seconds) Junction Temperature Storage Temperature Electrostatic Discharge (ESD) Protection Level(2) HBM CDM
(1)
Min.
-0.3 -0.3 -0.3
Max.
6 VIN+0.3 VIN+0.3 8 260 150
Units
V V V C/W C C C kV kV
-65 4.0 2.0
150
Notes: 1. Junction-to-ambient thermal resistance, JA, is a strong function of PCB material, board thickness, copper thickness and number of vias used, diameter of via used, available copper surface, and attached heat sink characteristics. A reasonable estimated value for JA for zero air flow at 0.5W is 60C/W. 2. Using Mil Std. 883E, method 3015.7 (Human Body Model) and EIA/JESD22C101-A (Charged Device Model).
Recommended Operating Conditions
The Recommended Operating Conditions table defines the conditions for actual device operation. Recommended operating conditions are specified to ensure optimal performance to the datasheet specifications. Fairchild does not recommend exceeding them or designing to absolute maximum ratings.
Parameter
Supply Voltage Range LED Forward Voltage Current Through Each LED Operating Ambient Temperature Operating Junction Temperature
Min.
2.5
Max.
5.5 4
Units
V V mA C C
2 -40 -40
30 +85 +125
(c) 2006 Fairchild Semiconductor Corporation FAN5617 Rev. 1.0.1
www.fairchildsemi.com
FAN5617 -- High-Efficiency, Constant-Current LED Driver with TinyWireTM Brightness Control
Electrical Specifications
Unless otherwise noted, VIN = 2.7V to 5.5V, ILED = 2mA to 20mA, EN = HIGH, NBR = 31, TA = -40C to +85C. Typical values are at 25C.
Parameter
Power Supplies
Input Under-Voltage Lockout Current Matching with Unmatched LEDs ILED/ISET Ratio Reference Voltage for Current Set Start-up Time
(4) (3)
Conditions
VIN Falling VIN Rising 2mA ILED 15mA, 2.8V LED VF <4V VIN = 3.6V, IOUT = 15mA ILED = 2 to 20mA COUT = 1F, VIN = 3.6V, ILED = 15mA ILED = 15mA VIN = 5.5V, IOUT = 5mA EN=0V, DATAIN = VIN VIN = 5.5V, VOUT = 0V LED Vf = 3.5V, ILED = 3 x 20mA LED Vf = 3.5V, ILED = 3 x 20mA VIN = 3.75V, LED Vf = 3.4V, ILED = 18mA
(5)
Min.
Typ.
Max.
1.6
Units
V V
2.3 0.6 240 230 588 200 255 260 600 270 170 250 0.1 65 3.9 2.9 90 0.8 1 150 15 1.2 1 80 6 +3 270 280 612 500 250
%
mV S mV A A mA V V V % MHz C C
Minimum Cathode Voltage Quiescent Current Shutdown Supply Current Output Short-Circuit Current VOUT Over-Voltage Protection VIN at Mode Transition from 1x to 1.5x VIN at Mode Transition from 1.5x to 2x Peak Efficiency
(6)
Oscillator Frequency Thermal Shutdown Threshold Thermal Shutdown Hysteresis
Logic Input Thresholds (EN and DATA)
Input Low Voltage Input High Voltage DATA Input Low Current VIN = 3.6V 1.25 110 0.4 V V A
Notes: 3. Current Matching refers to the absolute value of the difference in the current between the two LED branches:
Current Matching (%)
(I
LEDi
(I
- ILEDj x 100 + ILEDj
)
LEDi
)
where i, j = 1, 2, or 3.
4. 5. 6.
Start-up time is defined as the period from when the driver is turned on to the time when ILED is within 10% of its programmed value. When DATA remains low, the TinyWire interface is biased on and consumes up to 30A of current. Efficiency is expressed as a ratio between the electrical power into the LEDs and the total power consumed from the input power supply, expressed as:
Efficiency
V
i=1
3
LEDi
x ILEDi
VIN x IIN
Some vendors calculate the efficiency as a function of VOUT instead of LED VF. That method does not account for the power lost due to the cathode voltage not being equal to zero, which overstates efficiency by up to 5%.
(c) 2006 Fairchild Semiconductor Corporation FAN5617 Rev. 1.0.1
www.fairchildsemi.com
FAN5617 -- High-Efficiency, Constant-Current LED Driver with TinyWireTM Brightness Control
Typical Characteristics
Unless otherwise noted, VIN = 3.6V, TA = 25C, CIN = 4.7F, COUT = 1F, CAP1 = CAP2 = 0.1F, the FAN5617 driving three LEDs with VF = 3.3V at 20mA.
4.0 3.5 3.0 2.5 2.0 1.5 1.0 0.5 1X to 1.5X 1.5X to 2X 0 5 10 15 20 25
100 90 80
Input Voltage (V)
Efficiency (%)
70 60 50 40 30 20 10 0 2.0 2.5 3.0 3.5 4.0 4.5 5.0 5.5 ILED = 20mA ILED = 15mA ILED = 10mA ILED = 5mA
LED Current (mA)
Input Voltage (V)
Figure 3. Voltage Multiplication Ratio vs. LED Current
1.5
2.5
Figure 4. Efficiency vs. Input Voltage
% Change in LED Current
2.0
0.5
Quiescent Current (mA)
ILED = 20mA
1.5
1.0
-0.5
0.5
-1.5 2.7 3.2 3.7 4.2 4.7 5.2
0 2.7 3.2 3.7 4.2 4.7
ILED = 5mA
5.2
Input Voltage (V)
Input Voltage (V)
Figure 5. LED current vs. Input Voltage
200 180
Figure 6. Quiescent Current vs. Input Voltage
Minimum Cathode Voltage
160 140 120 100 80 60 40 20 0 1 5 9 13 VIN = 5.5V VIN = 3.6V VIN = 2.7V 17 21
LED Current (mA)
Figure 7. Minimum Cathode Voltage
Figure 8. Dimming Linearity
(c) 2006 Fairchild Semiconductor Corporation FAN5617 Rev. 1.0.1
www.fairchildsemi.com
FAN5617 -- High-Efficiency, Constant-Current LED Driver with TinyWireTM Brightness Control
Block Diagram
VIN
LINEAR REG
VOLTAGE SELECT
VOUT
EN
PGOOD
DATA
OSC
VIN
CAP1 CAP2
RSET
CURRENT SETTING AND RSET UVLO CONTROL LOGIC
CHARGE PUMP CONTROL AND SWITCHES MODE CHANGE
PGND
REFERENCE GENERATOR
VOUT
PGOOD
POWER GOOD
REGULATOR
VOLTAGE DETECT
IREF GND
CURRENT LIMITERS
Figure 9. IC Block Diagram
VIN CAP1 GND COUT
VIN CAP1 CAP2 COUT
GND
Figure 10. 2:1 Charge Pump Configuration VOUT = 2 X VIN
Figure 11. 3:2 Charge Pump Configuration VOUT = 1.5 X VIN
(c) 2006 Fairchild Semiconductor Corporation FAN5617 Rev. 1.0.1
www.fairchildsemi.com
FAN5617 -- High-Efficiency, Constant-Current LED Driver with TinyWireTM Brightness Control
Circuit Description
The FAN5617 switch capacitor DC/DC converter automatically configures its internal switches to achieve high efficiency, providing tightly-regulated output currents for the LEDs (see Figure 10 and Figure 11). An internal voltage detector determines which LED requires the highest voltage to sustain the pre-set current levels and adjusts the charge pump regulator accordingly. Each LED has its own linear current regulator. In addition, a voltage regulator controls the output voltage when the battery voltage is within a range where linear regulation can provide maximum efficiency. If the battery voltage is too low to sustain the LED current in linear mode, a fractional 3:2 charge pump is enabled. When the battery voltage drops and the mode can no longer sustain proper operation, the pump is automatically reconfigured to operate in 2:1 mode. As the battery discharges and the voltage decays, the FAN5617 switches between modes to maintain a constant current through the LEDs throughout the battery life. These transitions have hysteresis to prevent toggling. The internal supply voltage of the device is automatically selected from the VIN or VOUT pins, whichever has a higher voltage. The FAN5617 enters shutdown mode to reduce overall current consumption when the chip is disabled by the EN pin and control register. PWRUP goes low under any of the following conditions: 1. EN is low when power is first applied and no subsequent non- zero brightness commands are received EN goes from HIGH to LOW A zero brightness command is received
2. 3.
TinyWireTM Single-Wire Brightness Control
This IC features a digitally controlled static brightness adjustment to minimize both EMI and applications processor overhead. The brightness command consists of a 5-bit binary word (NBR). LED current is a multiple of the current through RSET: ILED = 156 * (NBR + 1) 32 * R SET
BIT3 0 0 0 0 0 0 0 0 1 1 1 1 1 1 1 1 0 0 0 0 0 0 0 0 1 1 1 1 1 1 1 1 BIT2 0 0 0 0 1 1 1 1 0 0 0 0 1 1 1 1 0 0 0 0 1 1 1 1 0 0 0 0 1 1 1 1
for NBR > 0
(1)
Start-up
When the FAN5617 is enabled, either by EN going high or on command from the TinyWireTM interface, the softstart circuit linearly ramps VOUT to limit the switcher's inrush current (see Figure 12). When power is first applied, the default IC brightness control register (NBR) is set to maximum brightness (31). If EN is low at initial power-up, the IC remains in a low-power state until either EN goes HIGH or a non-0 brightness command is received. If EN goes from HIGH to LOW, the IC is reset to the low-power state until either a new brightness command is received or EN is driven HIGH.
VIN
250s
VOUT PWRUP
Figure 12. Soft-Start An internal PWRUP signal turns on all of the IC's logic control circuitry and starts the charge pump. PWRUP is high under any of the following conditions: 1. 2. EN goes from low to high A non-zero brightness command is received
NBR 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31
BIT4 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1
BIT1 0 0 1 1 0 0 1 1 0 0 1 1 0 0 1 1 0 0 1 1 0 0 1 1 0 0 1 1 0 0 1 1
BIT0 0 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1
ILED/ISET 0 260 x 2/32 260 x 3/32 260 x 4/32 260 x 5/32 260 x 6/32 260 x 7/32 260 x 8/32 260 x 9/32 260 x 10/32 260 x 11/32 260 x 12/32 260 x 13/32 260 x 14/32 260 x 15/32 260 x 16/32 260 x 17/32 260 x 18/32 260 x 19/32 260 x 20/32 260 x 21/32 260 x 22/32 260 x 23/32 260 x 24/32 260 x 25/32 260 x 26/32 260 x 27/32 260 x 28/32 260 x 29/32 260 x 30/32 260 x 31/32 260 x 32/32
Table 1. NBR Data Dimming Values
(c) 2006 Fairchild Semiconductor Corporation FAN5617 Rev. 1.0.1
www.fairchildsemi.com
FAN5617 -- High-Efficiency, Constant-Current LED Driver with TinyWireTM Brightness Control
Circuit Description (Continued)
TLOW
DATA LATCHED IDLE
IDLE
LOGIC 1
LOGIC 0
THIGH
TBIT
TBIT
TRESET
BIT 0
BIT 1
BIT 4
STOP BIT
Figure 13.
TinyWireTM Protocol Timing
NBR data is shifted in LSB first on the DATA line, as shown in Figure 13. The TinyWire protocol operates over a wide range of TBIT times (see Table 3), allowing easy encoding of the brightness control bit-stream using a microcontroller software "bit-bang" loop. The 5-bit control word begins with the falling edge of DATA. If DATA is HIGH for a greater percentage of the time than it is low between falling edges, the bit is a "1." If DATA is LOW longer than it is HIGH, the bit is a "0." Observe the following timing rules to ensure proper data transmission: BIT =
0 1
Short-Circuit and Thermal Protection
In the event of an output voltage short circuit, the output current is limited to a typical value of 65mA. In addition, when the die temperature exceeds 150C, a reset occurs and remains in effect until the die cools down to 135C; at which time, the circuit restarts and resumes normal operation.
Selecting Capacitors
It is important to select the appropriate capacitor types and values for the FAN5617 circuit design. To reduce battery ripple, both CIN and COUT should be low-ESR capacitors. If necessary, the ripple can be further reduced by powering the IC through an RC input filter, as shown in Figure 14.
0.5
TLOW
> 75% TBIT < 25% TBIT
THIGH
< 25% TBIT > 75 % TBIT
Table 2. Data Bit Definition MIN.
TLOW THIGH TRESET 500ns 500ns 100s
MAX.
40s 40s
+ BATTERY -
10
4.7
VIN FAN5617 GND
Table 3. Timing Requirements Figure 14. Battery Ripple Reduction Time
MIN. MAX. MIN. MAX.
BIT =
0 0 1 1
TLOW
1500ns 40s 500ns 13s
THIGH
500ns 13s 1500ns 40s
TBIT
2s 53s 2s 53s
CAP1 and CAP2 should be MLCC capacitors of 0.1F to 1F for best efficiency in boost mode. For better ILED regulation, 1F bucket capacitors are recommended, particularly when ILED > 25mA and the battery discharges below 3V.
Table 4. Minimum and Maximum Bit Times Each falling edge of DATA clocks in the value of its preceding bit, necessitating a STOP pulse of at least TLOW(MIN) width. The command word, NBR (see Table 1. NBR Data Dimming Values), transfers to the internal registers and is valid at the rising edge of the STOP bit. A RESET is generated to the internal bit counters after the DATA line remains high for at least 100s. If less than five bits are received before the RESET occurs, no new data is transferred to the internal registers. If more than five bits are received before RESET, the first five bits are transferred at the rising edge of the sixth bit and subsequent bits are ignored.
PCB Layout Considerations
For best performance, a solid ground plane is recommended on the back side of the PCB. All capacitors should be placed as close to the IC as possible and connected with reasonably thick traces to minimize the ESL and ESR parasitics.
(c) 2006 Fairchild Semiconductor Corporation FAN5617 Rev. 1.0.1
www.fairchildsemi.com
FAN5617 -- High-Efficiency, Constant-Current LED Driver with TinyWireTM Brightness Control
Physical Dimensions
Dimensions are in millimeters (inches) unless otherwise noted.
Figure 15. 16-Lead, Molded Leadless Package (MLP), 3 x 3mm, .8mm Thick
(c) 2006 Fairchild Semiconductor Corporation FAN5617 Rev. 1.0.0
www.fairchildsemi.com 9
FAN5617 -- High-Efficiency, Constant-Current LED Driver with TinyWireTM Brightness Control
www.fairchildsemi.com
(c) 2006 Fairchild Semiconductor Corporation FAN5617 Rev. 1.0.0
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