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S P6685
700mA Buck/Boost Charge Pump LED Driver
June 2009 Rev. 2.0.0
GENERAL DESCRIPTION
The SP6685 is a current-regulated charge pump ideal for powering high brightness LEDs for camera flash applications. The charge pump can be set to regulated two current levels for FLASH and TORCH modes. The SP6685 automatically switches modes between step-up and step-down ensuring that LED current does not depend on the forward voltage. A low current sense reference voltage (50mV) allows the use of small 0603 current sensing resistors. The SP6685 is designed to operate from a single cell lithium-ion battery or fixed 3.3V or 5.0V power rails and is available in a RoHS compliant, "green"/halogen free space saving 10-pin 3mmx3mm DFN package.
APPLICATIONS
* White LED Torch/Flash for Cell Phone, DSCs and Camcorders * White LED Backlighting * Generic Lighting/Flash Application * General Purpose High Current Boost
FEATURES
* Output Current up to 700mA * Up to 94% Efficiency in Torch Mode * Minimum External Components: No Inductor * Adjustable FLASH Mode Current * 1x and 2x Charge Pump Operation * 2.4MHz High Frequency Operation * IQ < 1A in Shutdown * Built-In Soft Start Limit Inrush Current * Output Overvoltage Protection * Over current/Temperature Protection * 10pin 3x3mm DFN Package
TYPICAL APPLICATION DIAGRAM
Fig. 1: SP6685 Application Diagram
Exar Corporation 48720 Kato Road, Fremont CA 94538, USA
www.exar.com Tel. +1 510 668-7000 - Fax. +1 510 668-7001
S P6685
700mA Buck/Boost Charge Pump LED Driver
ABSOLUTE MAXIMUM RATINGS
These are stress ratings only and functional operation of the device at these ratings or any other above those indicated in the operation sections of the specifications below is not implied. Exposure to absolute maximum rating conditions for extended periods of time may affect reliability. VIN, VOUT ................................................... -0.3V to 6.0V Output Current Pulse (FLASH) .................................... 1A Output Current Continuous (TORCH) ........................ 0.4A VEN ................................................................. 0V to 7V Storage Temperature .............................. -65C to 150C Lead Temperature (Soldering, 10 sec) ................... 260C ESD Rating EN pin (HBM - Human Body Model) .......... 1kV ESD Rating All Other Pins (HBM) .............................. 2kV
OPERATING RATINGS
Input Voltage Range VIN ............................... 2.7V to 5.5V Operating Temperature Range ................... -40C to 85C Thermal Resistance JA ................................... 57.1C/W
ELECTRICAL SPECIFICATIONS
Specifications with standard type are for an Operating Junction Temperature of TJ = 25C only; limits applying over the full Operating Junction Temperature range are denoted by a "*". Minimum and Maximum limits are guaranteed through test, design, or statistical correlation. Typical values represent the most likely parametric norm at TJ = 25C, and are provided for reference purposes only. Unless otherwise indicated, VIN = 3.6, CIN = 4.7F, CFC = COUT = 1F. TA= -40C to 85C. Parameter Operating Input Voltage Quiescent Current Shutdown Current Oscillator Frequency Charge Pump Equivalent Resistance (x2 Mode) Charge Pump Equivalent Resistance (x1 Mode) FB Reference Voltage FB Reference Voltage FB Pin Current EN, Flash Logic Low EN, Flash Logic High EN, Flash Pin Current VOUT Turn-on Time Thermal Shutdown Temperature 250 145 1.3 0.5 500 138 45 2.4 5 0.6 150 50 0.8 162 55 0.5 0.4 Min. 2.7 0.5 2 1 A MHz Typ. Max. 5.5 3 Units V mA * * VIN = 2.7 - 5.5V FLASH = 0V ILOAD = 100 A FLASH = VIN, 2x Mode VIN = 5.5V, VEN = 0V VFB = 0V, VIN = 3.6V VIN = 3.6V * * * * * * VIN = 3.6V, FB within 90% of regulation FLASH = VIN, RSET = 88.7K FLASH = GND VFB = 0.3V Conditions

mV mV A V V A S
o
C
(c) 2009 Exar Corporation
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S P6685
700mA Buck/Boost Charge Pump LED Driver
BLOCK DIAGRAM
Fig. 2: SP6685 Block Diagram
PIN ASSIGNEMENT
Fig. 3: SP6685 Pin Assignment
(c) 2009 Exar Corporation
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S P6685
700mA Buck/Boost Charge Pump LED Driver
PIN DESCRIPTION
Name VIN C1 C2 Pin Number 1 2 3 Description Input voltage for the charge pump. Decouple with 4.7F ceramic capacitor close to the pins of the IC. Positive input for the external fly capacitor. Connect a ceramic 1F capacitor close to the pins of the IC. Negative input for the external fly capacitor. Connect a ceramic 1F capacitor close to the pins of the IC. Logic input to toggle between FLASH and TORCH mode. In TORCH Mode FB is regulated to the internal 50mV reference. In FLASH Mode FB reference voltage can be adjusted by changing the resistor from RSET pin to ground. Choose the external current sense Resistor (RSENSE) based on desired current in TORCH Mode. Shutdown control input. Connect to VIN for normal operation, connect to ground for shutdown. Connect a resistor from this pin to ground. When in FLASH Mode (FLASH = High) this resistor sets the current regulation point according to the following: VFB = (1.26V/RSET)*11.2K Feedback input for the current control loop. Connect directly to the current sense resistor. Internal ground pin. Control circuitry returns current to this pin. Power ground pin. Fly capacitor current returns through this pin. Charge Pump Output Voltage. Decouple with an external capacitor. At least 1F is recommended. Higher capacitor values reduce output ripple.
FLASH
4
EN RSET FB SGND PGND VOUT
5 6 7 8 9 10
ORDERING INFORMATION
Part Number Temperature Range -40CTA+85C Marking SP66 85ER WWX SP66 85ER WWX Package Packing Quantity Bulk Note 1 RoHS Compliant Halogen Free RoHS Compliant Halogen Free Note 2
SP6685ER-L
DFN-10
SP6685ER-L/TR SP6685EB
-40CTA+85C SP6685 Evaluation Board
DFN-10
3K/Tape & Reel
"WW" = Work Week - "X" = Lot Number
(c) 2009 Exar Corporation
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S P6685
700mA Buck/Boost Charge Pump LED Driver
TYPICAL PERFORMANCE CHARACTERISTICS
All data taken at VIN = 3.6V, Typical Application Circuit, D1 = Luxeon LXCL-PWF1, TJ = TA = 25C, unless otherwise specified.
Fig. 4: TORCH Mode Output Current
Fig. 5: FLASH Mode Output Current
Fig. 6: TORCH Mode Output Efficiency
Fig. 7: FLASH Mode Output Efficiency
Fig. 8: Ripple 1x FLASH Mode 700mA, CH1 = VIN CH2 = VOUT, VIN = 4.2V, CIN = 10F, CF = 1F, COUT = 4.7F
Fig. 9: Ripple 2x FLASH Mode 700mA. CH1 = VIN CH2 = VOUT, VIN = 3.6V, CIN = 10F, CF = 1F, COUT = 4.7F
(c) 2009 Exar Corporation
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700mA Buck/Boost Charge Pump LED Driver
Fig. 10: Ripple 1x TORCH Mode 200mA. CH1 = VIN CH2 = VOUT, VIN = 4.2V, CIN = 10F, CF = 1F, COUT = 4.7F
Fig. 11: Ripple 2x TORCH Mode 200mA. CH1 = VIN CH2 = VOUT, VIN = 3.0V, CIN = 10F, CF = 1F, COUT = 4.7F
Fig. 12: COUT = 4.7F
Fig. 13: COUT = 4.7F
Fig. 14: CIN = 10F
Fig. 15: CIN = 10F
(c) 2009 Exar Corporation
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S P6685
700mA Buck/Boost Charge Pump LED Driver
Fig. 16: Output Current vs Supply Voltage
Fig. 17: Efficiency ve Supply Voltage
Fig. 18: Battery Current vs Supply Voltage
Fig. 18: D1 = AOT 3228HPW0303B LED, RSENSE = 0.33 RSET = 162K, CIN = 4.7F, CF = 0.47F, COUT = 1F
Fig. 20: D1 = AOT 3228HPW0303B LED, RSENSE = 0.33 RSET = 162K, CIN = 4.7F, CF = 0.47F, COUT = 1F
Fig. 21: D1 = AOT 3228HPW0303B LED, RSENSE = 0.33 RSET = 162K, CIN = 4.7F, CF = 0.47F, COUT = 1F
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S P6685
700mA Buck/Boost Charge Pump LED Driver
Fig. 22: D1 = AOT 6060HPW0305B LED, RSENSE = 0.33 RSET = 75K, CIN = 4.7F, CF = 1F, COUT = 1F
Fig. 23: D1 = AOT 6060HPW0305B LED, RSENSE = 0.33 RSET = 75K, CIN = 4.7F, CF = 1F, COUT = 1F
Fig. 19: D1 = AOT 6060HPW0305B LED, RSENSE = 0.33 RSET = 75K, CIN = 4.7F, CF = 1F, COUT = 1F
Fig. 20: D1 = AOT 2015HPW1915B LED, RSENSE = 0.22 RSET = 80.6K, CIN = 4.7F, CF = 1F, COUT = 1F
Fig. 26: D1 = AOT 2015HPW1915B LED, RSENSE = 0.22 RSET = 80.6K, CIN = 4.7F, CF = 1F, COUT = 1F
Fig. 27: D1 = AOT 2015HPW1915B LED, RSENSE = 0.22 RSET = 80.6K, CIN = 4.7F, CF = 1F, COUT = 1F
(c) 2009 Exar Corporation
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S P6685
700mA Buck/Boost Charge Pump LED Driver
Fig. 28: Startup 200mA Torch VIN = 3.6V, VOUT = 3.2V
Fig. 29: Startup 700mA Flash VIN = 3.6V, VOUT = 3.6V
Fig. 30: Torch in 1X to Flash in 1X Mode, VIN = 4.2V CH1 = FLASH, CH2 = VOUT, CH3 = VFB, CH4 = IOUT 1A/div
Fig. 31: Torch in 1X to Flash in 2X Mode, VIN = 3.6V CH1 = FLASH, CH2 = VOUT, CH3 = VFB, CH4 = IOUT 1A/div
Fig. 32: Efficiency See fig.34 for Application Circuit
Fig. 33: Output Current See fig.34 for Application Circuit
(c) 2009 Exar Corporation
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S P6685
700mA Buck/Boost Charge Pump LED Driver
APPLICATION INFORMATION
The SP6685 can be used with multiple LEDs in parallel as shown in figure 34. For best performance, the LEDs should be in a single package, preferably from a single die to have better matching for forward voltage Vf for a given forward current If. In practice, if the Vf of one LED is higher than the others, it will consume a larger If, which will raise its temperature which will then cause its Vf to reduce, correcting the imbalance. The overall current will be the sum of the individual currents, for example Itotal = 4*ILED.
Fig. 34: Multiple LED Flash Circuit
THEORY OF OPERATION
The SP6685 is a charge pump regulator designed for converting a Li-Ion battery voltage of 2.7V to 4.2V to drive a white LED used in digital still camera Flash and Torch applications. The SP6685 has two modes of operation which are pin selectable for either Flash or Torch. Flash mode is usually used with a pulse of about 200 to 300 millisecond to generate a high intensity Flash. Torch can be used continuously at a lower output current than Flash and is often used for several seconds in a digital still camera "movie" mode. The SP6685 also has two modes of operation to control the output current: the 1X mode and 2X mode. Operation begins after the enable pin EN receives a logic high, the bandgap reference wakes up after about 200sec, and then SP6685 goes through a soft-start mode designed to reduce inrush current. The SP6685 starts in the 1X mode,
(c) 2009 Exar Corporation 10/14
which acts like a linear regulator to control the output current by continuously monitoring the feedback pin FB. In 1X mode, if the SP6685 auto detects a dropout condition, which is when the FB pin is below the regulation point for more than 32 cycles of the internal clock, the SP6685 automatically switches to the 2X mode. The SP6685 remains in the 2X mode until one of four things happens: 1) the enable pin EN has been toggled, 2) the Flash pin has changed from High to Low, 3) VIN is cycled. 4) a thermal fault occurs. The 2X mode is the charge pump mode where the output can be pumped as high as two times the input voltage, provided the output does not exceed the maximum voltage for the SP6685, which is internally limited to about 5.5V. In the 2X mode, as in the 1X mode, the output current is regulated by the voltage at the FB pin.
Rev. 2.0.0
S P6685
700mA Buck/Boost Charge Pump LED Driver
In the Torch mode, (Flash = GND) the Flash pin is set to logic low and the SP6685 IFB pin regulates to 50mV output: VFB = 50mV (Torch Mode) current exceeds approximately 1Amp, then the over current protection circuitry shuts off the output switches to protect the chip.
COMPONENT SELECTION
The SP6685 charge pump circuit requires 3 capacitors: 4.7F input, 1F output and 1F fly capacitor are typically recommended. For the input capacitor, a larger value of 10F will help reduce input voltage ripple for applications sensitive to ripple on the battery voltage. All the capacitors should be surface mount ceramic for low lead inductance necessary at the 2.4MHz switching frequency of the SP6685 and to obtain low ESR, which improves bypassing on the input and output and improves output voltage drive by reducing output resistance. Ceramic capacitors with X5R or X7R temperature grade are recommended for most applications. A selection of recommended capacitors is included in Table 1 below.
Manufacturer muRata muRata muRata Part Number GRM155R60J105K GRM21BR60J106K Value 1F/6.3V 10F/6.3V Size/Type 0402/X5R 0603/X5R 0805/X5R
When in Flash mode, (Flash = VIN), the FB regulation voltage is set by the resistor RSET connected between the RSET pin and SGND and the equation: VFB = (1.26V/ RSET)*11.2K (Flash Mode)
Where the 1.26V is the internal bandgap reference voltage and the 11.2K is an internal resistance used to scale the RSET current. Typical values of RSET are 40K to 180K for a range of VFB = 300mV to 75mV in Flash mode. The output current is then set in either Flash or Torch mode by the equation: IOUT = VFB / Rsense
GRM188R60J475K 4.7F/6.3V
Table 1: Recommended Capacitors
OVERTEMPERATURE PROTECTION
When the temperature of the SP6685 rises above 145C, the over temperature protection circuitry turns off the output switches to prevent damage to the device. If the temperature drops back down below 135C, the part automatically recovers and executes a soft start cycle. The input and output capacitors should be located as close to the VIN and VOUT pins as possible to obtain best bypassing, and the returns should be connected directly to the PGND pin or to the thermal pad ground located under the SP6685. The fly capacitor should be located as close to the C1 and C2 pins as possible. See typical circuit layout (page 13) for details on the recommended layout. To obtain lower output ripple, the COUT value can be increased from 1F to 2.2F or 4.7F with a corresponding decrease in output ripple as shown in the Typical Performance Characteristic curves. For output currents of 500mA to 700mA, the recommended CFC fly capacitor value of 1F should be used. Output currents in Flash of 100mA to 400mA can use a 0.47F CFc but a minimum 1F COUT is still needed.
OVERVOLTAGE PROTECTION
The SP6685 has over voltage protection. If the output voltage rises above the 5.5V threshold, the over voltage protection shuts off all of the output switches to prevent the output voltage from rising further. When the output decreases below 5.5V, the device resumes normal operation.
OVERCURRENT PROTECTION
The over current protection circuitry monitors the average current out of the VOUT = 50mV (Torch Mode) pin. If the average output
(c) 2009 Exar Corporation 11/14
Rev. 2.0.0
S P6685
700mA Buck/Boost Charge Pump LED Driver
RESISTOR SELECTION
The sense resistor RSENSE is determined by the value needed in the Torch mode for the desired output current by the equation: RSENSE = VFB/IOUT Where VFB = 50mV (Torch Mode) Once the RSENSE resistor has been selected for Torch mode, the VFB voltage can be selected for Flash mode using the following equation: VFB = IOUT * RSENSE (Flash Mode) Where IOUT is for Flash Mode. Next, the RSET resistor can be selected for Flash mode using the following equation: RSET = (1.26V/ VFB)*11.2K (Flash Mode) For an example of 200mA Torch mode and 600mA Flash mode, the values RSENSE = 0.25, VFB = 150mV (Flash Mode), and RSET = 94K are calculated. The power obtained in the Flash mode would be: PFLASH = VFB *IOUT = 150mV*600mA = 90mW. The typical 0603 surface mount resistor is rated 1/10 Watt continuous power and 1/5 Watt pulsed power, more than enough for this application. For other applications, the PFLASH power can be calculated and resistor size selected. The RSENSE resistor is recommended to be size 0603 for most applications. The range of typical resistor values and sizes are shown in table 2.
Part Ref. RSET RSET RSET RSET RSET RSET RSET RSET RSET RSET RSENSE RSENSE RSENSE RSENSE RSENSE
Value 68K 75K 82K 91K 100K 110K 120K 130K 140K 150K 0.22 0.27 0.33 0.39 0.47
Tolerance 5% 5% 5% 5% 5% 5% 5% 5% 5% 5% 5% 5% 5% 5% 5%
Size 0402 0402 0402 0402 0402 0402 0402 0402 0402 0402 0603 0603 0603 0603 0603
Table 2: Resistor Value and Sizes
EVALUATION BOARD CIRCUIT LAYOUT
(c) 2009 Exar Corporation
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700mA Buck/Boost Charge Pump LED Driver
PACKAGE SPECIFICATION 10-PIN DFN
(c) 2009 Exar Corporation
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700mA Buck/Boost Charge Pump LED Driver
REVISION HISTORY
Revision 2.0.0 Date 06/18/2009 Reformatted to corporate standard Updated ESD level for EN pin. Description
FOR FURTHER ASSISTANCE
Email: Exar Technical Documentation: customersupport@exar.com http://www.exar.com/TechDoc/default.aspx?
EXAR CORPORATION HEADQUARTERS AND SALES OFFICES
48720 Kato Road Fremont, CA 94538 - USA Tel.: +1 (510) 668-7000 Fax: +1 (510) 668-7030 www.exar.com
NOTICE
EXAR Corporation reserves the right to make changes to the products contained in this publication in order to improve design, performance or reliability. EXAR Corporation assumes no responsibility for the use of any circuits described herein, conveys no license under any patent or other right, and makes no representation that the circuits are free of patent infringement. Charts and schedules contained here in are only for illustration purposes and may vary depending upon a user's specific application. While the information in this publication has been carefully checked; no responsibility, however, is assumed for inaccuracies. EXAR Corporation does not recommend the use of any of its products in life support applications where the failure malfunction of the product can reasonably be expected to cause failure of the life support system or to significantly affect safety or effectiveness. Products are not authorized for use in such applications unless EXAR Corporation receives, writing, assurances to its satisfaction that: (a) the risk of injury or damage has been minimized; (b) the user assumes such risks; (c) potential liability of EXAR Corporation is adequately protected under the circumstances. Reproduction, in part or whole, without the prior written consent of EXAR Corporation is prohibited. or its in all
(c) 2009 Exar Corporation
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