SP7686ER-L/TR

SP7686/SP7686A Constant Current Flash Driver in DFN 2mm x 3mm January 2010 Rev. 2.1.0 GENERAL DESCRIPTION APPLICATIONS The SP7686/SP7686A are current regulated charge pumps ideal for powering high power, high brightness LEDs for camera FLASH applications of up to 500mA. The charge pump automatically switches between step-up and step-down modes ensuring that the LED current does not depend on the forward voltage. A low current sense reference voltage (60mV to 360mV) allows the use of small 0603 current sensing resistors. The SP7686 has a DAC programmable feedback reference voltage allowing the user to precisely set FLASH and TORCH output current levels, while the fixed version SP7686A has set levels of FLASH and TORCH reference voltage. Both parts have overvoltage, over-current, over-temperature and FLASH time-out protection features. The SP7686 and SP7686A are offered in a RoHS compliant “green”/halogen free space saving 8-pin 2x3mm DFN package. • Cell Phone Flash • Cell Phone Torch • General LED applications FEATURES • Output current up to 500mA • Up to 94% efficiency • Single Wire serial interface • 2.4MHz switching frequency • FB Reference voltage adjusts in 10mV steps from 60mV to 360mV • 10nA Shutdown • PWM brightness control for DAC • Fast turn-on ( 350μsec, VEN < 0.4V (SP7686A) Quiescent Current 300 μA 0 mV FB Voltage for DAC=00001 58 mV Open loop comparator trip voltage FB Voltage for DAC=11111 350 mV Open loop comparator trip voltage FB DAC LSB 9.7 mV Operating Input Current FB Voltage for DAC=00000 FB Voltage Accuracy -14 14 % • Condition 1 VFB = 0mV, DAC=00000 • • Variation from specified VFB FB voltage (SP7686A, Torch) 54 60 66 mV • Flash = LOW, Open loop comparator trip voltage FB Voltage (SP7686A, Flash) 147 160 173 mV • Flash = HIGH, Open loop comparator trip voltage 0.5 μA • VFB =0.3V 2.0 2.4 2.8 MHz • Equivalent Resistance, 1x mode 0.6 1.4 Ω • Equivalent Resistance, 2x mode 8 FB Pin Current Switching Frequency Thermal Regulation Ω 0.01 Thermal Shutdown Die Temperature %/°C VFB = 60mV 140 °C Driver turns off Thermal Shutdown Hysteresis 15 °C Driver turns on again Settle time (TS) after last count 15 Ctrl Input Data Rate 0.5 50 1 μs μs CTRL minimum pulse width Wake-up time (TPOR) from Vin off 600 μs • VIN pin low to high, 1 CTRL pulse, VFB =0mV Wake-up time (TON) from shutdown 200 μs • 1 CTRL pulse or (EN pin low to high SP7686A) 25 75 μs 50 μs 200 350 μs • CTRL pin high to low 3.5 4.2 s • VFB>120mV (SP7686, 11 CTRL pulses), FLASH= high (SP7686A) 0.4 V • Driver shutdown Delay time (TDELAY) from 1st to 2nd pulse Turn-off time (TOFF) into shutdown Turn-off time (TOFFC )into shutdown Time Duration before shutdown Logic low voltage © 2010 Exar Corporation 2.8 2/16 1st to 2nd CTRL pulse time delay – guaranteed by design EN pin high to low (SP7686A) Rev. 2.1.0 SP7686/SP7686A Constant Current Flash Driver in DFN 2mm x 3mm Parameter Logic high voltage Min. Typ. Max. 1.4 CTRL, EN pin current 0.5 Units Conditions V • Driver enabled μA • (EN pin is SP7686A only) Note 1: Guaranteed maximum allowable power dissipation depends on the ambient temperature BLOCK DIAGRAM: SP7686 Fig. 2: SP7686 Block Diagram BLOCK DIAGRAM: SP7686A Fig. 3: SP7686A Block Diagram © 2010 Exar Corporation 3/16 Rev. 2.1.0 SP7686/SP7686A Constant Current Flash Driver in DFN 2mm x 3mm PIN ASSIGNMENT   SP7686                                                            SP7686A Fig. 4: SP7686 and SP7686A Pin Assignment PIN DESCRIPTION: SP7686 Name Pin Number 1 VIN 2, 3 C1, C2 4 CTRL 5 FB 6 SGND 7 PGND 8 VOUT © 2010 Exar Corporation Description Power supply input. Place a 10μF decoupling capacitor next to this pin. Connect an external 0.22μF flying capacitor between these pins This pin is used to control LED current. Once enabled the adjustable driver counts positive going edges at this pin and sequentially increases FB voltage with 10mV steps to a maximum 31 steps or 360mV. When this pin is held LOW for longer than 200μs the SP7686 enters shutdown. The part can be enabled using this pin. The first positive edge resets the part. A second positive edge sets the part to VFB=0. A third positive going edge will increase FB voltage to 60mV and subsequent positive edges increment VFB in 10mV steps. The voltage level can increase only and must be reset to zero by the 200μs shutdown timer in order to go to a lower current value. The part will be limited to a 3.5s on time when FB voltage is set to 120mV and above. This pin cannot be left open. Current feedback input. Place an external current sense resistor from this pin to ground. Voltage at this pin will be internally compared to the DAC output (60mV – 360mV). Ground pin for SP7686 bias and reference (low current). Ground pin for power (high current). Output voltage of the internal charge pump. Connect the LED between this pin and the current sense resistor. Voltage at this pin will be regulated in order to maintain constant LED current. Place a 2.2μF ceramic capacitor next to this pin. 4/16 Rev. 2.1.0 SP7686/SP7686A Constant Current Flash Driver in DFN 2mm x 3mm PIN DESCRIPTION: SP7686A Name Pin Number 1 VIN 2, 3 C1, C2 Connect an external 0.22μF flying capacitor between these pins 4 FLASH The SP7686A uses the flash pin to switch between two internally preset voltage levels, for Flash and Torch mode. The part is enabled and disabled by the separate ENABLE pin. The part has a 3.5s maximum on time in Flash mode. After a 3.5s timeout occurs the part shuts down and can be enabled by the FLASH or ENABLE pins. This pin cannot be left open. 5 FB Current feedback input. Place an external current sense resistor from this pin to ground. Voltage at this pin will be internally compared to 60mV or 160mV depending on the logic level of the FLASH pin. 6 EN The SP7686A has this enable/shutdown pin. (Logic high = enable, logic low = shutdown). Used to immediately disable the driver and PWM brightness control. There is an internal pull down on this pin. 7 PGND 8 VOUT Description Power supply input. Place a 10μF decoupling capacitor next to this pin. Ground pin for power (high current). Output voltage of the internal charge pump. Connect the LED between this pin and the current sense resistor. Voltage at this pin will be regulated in order to maintain constant LED current. Place a 2.2μF ceramic capacitor next to this pin. ORDERING INFORMATION Temperature Range Marking Package Packing Quantity SP7686AER-L -40°C≤TA≤+85°C SP7686A YYWWX 2x3mm DFN8 Bulk Lead Free and Halogen Free MSL L1@250°C SP7686AER-L/TR -40°C≤TA≤+85°C SP7686A YYWWX 2x3mm DFN8 3K/Tape & Reel Lead Free and Halogen Free MSL L1@250°C SP7686ER-L -40°C≤TA≤+85°C SP7686 YYWWX 2x3mm DFN8 Bulk Lead Free and Halogen Free MSL L1@250°C SP7686ER-L/TR -40°C≤TA≤+85°C SP7686 YYWWX 2x3mm DFN8 3K/Tape & Reel Lead Free and Halogen Free MSL L1@250°C Part Number SP7686EB Note 1 Note 2 SP7686EB “YY” = Year – “WW” = Work Week – “X” = Lot Number © 2010 Exar Corporation 5/16 Rev. 2.1.0 SP7686/SP7686A Constant Current Flash Driver in DFN 2mm x 3mm TYPICAL PERFORMANCE CHARACTERISTICS All data taken atVIN = 3.6V, TJ = TA = 25°C, unless otherwise specified, Typical Application Circuit, D1 = Luxeon LXCL-PWF3. 550 400 500 350 450 300 400 V F B (m V ) 250 Iout (mA) 350 200 300 250 150 Vin=4.2V 100 Vin=3.6V 200 50 Vin=3.0V 150 Vin=4.2V Vin=3.6V Vin=3.0V 100 0 50 3 6 9 12 15 18 21 24 27 30 33 0 3 Vctrl Pulse Efficiency (%) Iout (mA) 400 Flash 440mA Torch 160mA Torch 88mA 100 0 3.0 3.3 3.6 3.9 4.2 15 18 21 24 27 30 33 100 90 80 70 60 50 40 30 20 10 0 Flash 440mA Torch 160mA Torch 88mA 3.0 3.3 3.6 3.9 4.2 Vin (V) Vin (V) Fig. 5: SP7686 Output Current vs Input Voltage © 2010 Exar Corporation 12 Fig. 4: SP7686 IOUT vs CTRL Pulses 500 200 9 Vctrl Pulse Fig. 3: SP7686 VFB vs CTRL Pulses 300 6 Fig. 6: SP7686 Efficiency 6/16 Rev. 2.1.0 SP7686/SP7686A Constant Current Flash Driver in DFN 2mm x 3mm CTRL CTRL VOUT VOUT VFB VFB IIN: 0.5A/div IIN: 0.5A/div Fig. 8: SP7686 Startup with 32 CTRL Pulses, VIN=4.2V Fig. 7: SP7686 Startup with 3 CTRL Pulses, VIN=4.2V CTRL CTRL VOUT VOUT VFB VFB IIN: 0.5A/div IIN: 0.5A/div Fig. 10: SP7686 Vout Shorted to GND, VIN = 5.5V Fig. 9: SP7686 Turn-off time into SHDN 100 CTRL 90 Efficiency (%) VOUT VFB 80 70 60 50 Flash 450mA 40 IIN: 0.5A/div Torch 150mA 30 2.7 3 3.3 3.6 3.9 4.2 Vin (V) Fig. 12: SP7686A Efficiency Fig. 11: SP7686 LED Open, VIN = 4.2V © 2010 Exar Corporation 7/16 Rev. 2.1.0 SP7686/SP7686A Constant Current Flash Driver in DFN 2mm x 3mm 500 200 150 Iout (mA) Iout (mA) 400 300 200 100 50 100 0 0 2.7 3.0 3.3 3.6 3.9 4.2 2.7 3.0 Vin (V) 3.3 3.6 3.9 4.2 Vin (V) Fig. 14: SP7686A Torch Mode Output Current Fig. 13: SP7686A Flash Mode Output Current CTRL CTRL VOUT VOUT VFB VFB SP7686A Time-out Flash to Shutdown, VIN=4.2V SP7686A Turn-off to Shutdown, VIN=4.2V EN EN VOUT VOUT VFB VFB IIN 1A/div IIN 1A/div SP7686A Flash Mode 2X, VIN=3.4V SP7686A Flash Mode 1X, VIN=4.2V © 2010 Exar Corporation 8/16 Rev. 2.1.0 SP7686/SP7686A Constant Current Flash Driver in DFN 2mm x 3mm EN EN VOUT VOUT VFB VFB IIN 0.5A/div IIN 0.5A/div SP7686A Torch Mode 1X, VIN=4.2V SP7686A Torch Mode 2X, VIN=2.9V FLASH FLASH VOUT VOUT VFB VFB SP7686A 1X Torch to 2X Flash, VIN=3.3V SP7686A 2X Flash to 1X Torch, VIN=3.3V SP7686A Flash 1X Ripple, VIN=4.2V © 2010 Exar Corporation SP7686A Torch 1X Ripple, VIN=3.0V 9/16 Rev. 2.1.0 SP7686/SP7686A Constant Current Flash Driver in DFN 2mm x 3mm pin cannot be left open. When in Flash mode, (Flash = VIN), the FB regulation voltage is set to 160mV. When in Torch mode, (Flash = GND), the FB regulation voltage is set to 60mV. The output current is then set in either Flash or Torch mode by the equation: THEORY OF OPERATION OVERVIEW The SP7686 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 SP7686 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 milliseconds 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 SP7686 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 200μsec, and then SP7686 goes through a softstart mode designed to reduce inrush current. The SP7686 starts in the 1X mode, which acts like a linear regulator to control the output current by continuously monitoring the feedback pin FB. In 1X mode, if the SP7686 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 SP7686 automatically switches to the 2X mode. The SP7686 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 or, 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 SP7686, 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. IOUT = VFB / RSENSE. SP7686 The digital controlled current driver (SP7686) uses the CTRL pin as a serial data input to a DAC to set the FB voltage. The CTRL pin is used to control LED current. Once enabled the adjustable driver counts positive going edges at this pin and sequentially increases the FB voltage from 60mV with 10mV steps to a maximum 31 steps or 360mV. When this pin is held LOW for longer than 200μs the SP7686 enters shutdown. The part can be enabled using this pin. The first positive edge resets the part. A second positive edge sets the part to VFB=0. A third positive going edge will increase FB voltage to 58mV and subsequent positive edges increment VFB in 9.7mV steps. The voltage level can increase only and must be reset to zero by the 200μs shutdown timer in order to go to a lower current value. The part will be limited to a 3.5s on time when FB voltage is set to 120mV and above. The CTRL pin cannot be left open. FLASH TIMEOUT PROTECTION Due to the high currents typically available in Flash mode, it is necessary to protect the white LED from damage if left on too long. The SP7686 has a timeout in Flash mode of approximately 3.5 seconds after which it will shutdown operation. Operation will not begin again in Flash mode until the Enable pin has been set Low and then High again. OVER TEMPERATURE PROTECTION SP7686A When the temperature of the SP7686 Rises above 140 degrees Celsius, the over temperature protection circuitry turns off the output switches to prevent damage to the device. If the temperature drops back down below 125 degrees Celsius, the part automatically recovers and executes a soft start cycle. The fixed current driver (SP7686A) uses the flash pin to switch between two internally preset voltage levels, for Flash and Torch mode. The part is enabled and disabled by the separate ENABLE pin. The part has a 3.5s maximum on time in Flash mode. After a 3.5s timeout occurs the part shuts down and can be enabled by the FLASH or ENABLE pins. This © 2010 Exar Corporation 10/16 Rev. 2.1.0 SP7686/SP7686A Constant Current Flash Driver in DFN 2mm x 3mm OVERVOLTAGE PROTECTION APPLICATIONS INFORMATION The SP7686 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. The SP7686 can be used with multiple LEDs in parallel as shown below. 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. OVERCURRENT PROTECTION The overcurrent protection circuitry monitors the average current out of the VOUT pin. If the average output current exceeds approximately 1.5Amp, then the overcurrent protection circuitry shuts off the output switches to protect the chip. Figure 24. Fig. 1: SP7686 with 4 LEDs in parallel Fig. 2: SP7686A with 4 LEDs in parallel © 2010 Exar Corporation 11/16 Rev. 2.1.0 SP7686/SP7686A Constant Current Flash Driver in DFN 2mm x 3mm APPLICATIONS INFORMATION CONT’D work but input voltage ripple will increase and may effect regulation. The SP7686 charge pump circuit requires 3 capacitors: 10μF input, 2.2μF output and 0.22μF fly capacitor are typically recommended. For the input capacitor, a value of 10μF 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 SP7686 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. RESISTOR SELECTION FOR THE SP7686A The 7686A part has fixed FB voltages in Torch and Flash modes so the sense resistor RSENSE is determined by the value needed in the Torch or Flash mode for the desired output current by the equation: RSENSE=VFB/IOUT where VFB=60mV (Torch Mode) RSENSE=VFB/IOUT where VFB=160mV(Flash Mode) Once the RSENSE resistor has been selected for one mode, the IOUT can be selected for the other mode using the following equation: IOUT = VFB / RSENSE Using an example of Torch current of 180mA and Flash current of 450mA, calculated RSENSE for Torch is 0.06 /0.180 = 0.333 Ohms. Use a standard value of 0.33 Ohms. IOUT for Flash mode is 0.16/0.33 = 480mA 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 SP7686. The fly capacitor should be located as close to the C1 and C2 pins as possible. See the RECOMMENDED LAYOUT section for details on the recommended layout. The power obtained in the Flash mode would be: PFLASH = VFB *IOUT = 160mV*480mA ~ 77mW. 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 here in Table 2. To obtain low output ripple, a value of 2.2μF is recommended for COUT. For all output currents the value for CFLY of 0.22μF is recommended. For best regulation and low input current ripple the input capacitor value of 10μF is recommended. A smaller 4.7μF for Cin will Manufacturers/ Website Part Number TDK/www.tdk.com TDK/www.tdk.com TDK/www.tdk.com TDK/www.tdk.com TDK/www.tdk.com Murata/www.murata.com Murata/www.murata.com Murata/www.murata.com Murata/www.murata.com Murata/www.murata.com C1005X5R0J224K C1005X5R0J105K C1608X5R0J225K C1608X5R0J475K C1608X5R0J107M GRM155R60J224KE19D GRM155R60J105KE19D GRM188R60J225KE19D GRM188R60J475KE19D GRM188R60J106ME19D Capacitance/ Voltage 0.22uF/6.3V 1uF/6.3V 2.2uF/6.3V 4.7uF/6.3V 10uF/6.3V 0.22uF/6.3V 1uF/6.3V 2.2uF/6.3V 4.7uF/6.3V 10uF/6.3V Capacitor Size/Type/Thickness ESR at 100kHz 0402/X5R/0.55mm 0402/X5R/0.55mm 0603/X5R/0.9mm 0603/X5R/0.9mm 0603/X5R/0.9mm 0402/X5R/0.55mm 0402/X5R/0.55mm 0603/X5R/0.8mm 0603/X5R/0.8mm 0603/X5R/0.9mm 0.05 0.03 0.03 0.02 0.02 0.05 0.03 0.03 0.02 0.02 Table 1: Capacitor Selection © 2010 Exar Corporation 12/16 Rev. 2.1.0 SP7686/SP7686A Constant Current Flash Driver in DFN 2mm x 3mm Part Reference Value RSENSE RSENSE RSENSE RSENSE RSENSE RSENSE RSENSE 0.22ohms 0.27ohms 0.33ohms 0.39ohms 0.47ohms 0.56ohms 0.68ohms Tolerance Size 1% 1% 1% 1% 1% 1% 1% 0603 0603 0603 0603 0603 0603 0603 or or or or or or or 5% 5% 5% 5% 5% 5% 5% Manufacturers Panasonic Panasonic Panasonic Panasonic Panasonic Panasonic Panasonic or or or or or or or Vishay Vishay Vishay Vishay Vishay Vishay Vishay Table 2: Resistor Selection the CTRL pin goes low for more than 200μs the part will shutdown. See the timing diagrams in the Typical Performance Characteristics. The first pulse turns on the SP7686. The first pulse needs to occur at least 600μsec after VIN is applied in order to activate after the power on reset (POR). The second pulse resets the DAC to 0. The timing between the first and second pulse needs to be 25μsec typical to as long as 75μsec. After the second pulse the feedback voltage remains at ground. The third pulse sets the feedback voltage to 58mV. Subsequent pulses set the feedback voltage in 9.7mV steps as shown previously in the Typical Performance Characteristics. RESISTOR SELECTION FOR SP7686 The SP7686 part uses an internal 5 bit DAC to set the LED current. The DAC input is at the CTRL pin. The user inputs a pulse train of up to 1MHz to set the LED current. The DAC sets the feedback voltage point from 58mV to 350mV in 9.7mV steps. The LED current is determined by the equation: ILED = VFB/RSENSE The curves below show the feedback and LED currents for the CTRL pin pulse count and standard RSENSE resistor values. After the desired count is reached the CTRL input must remain high to hold the count. If © 2010 Exar Corporation 13/16 Rev. 2.1.0 SP7686/SP7686A Constant Current Flash Driver in DFN 2mm x 3mm Fig. xx: Example Board Layout Fig. xx: PCB Footprint for 2x3mm 8pin DFN Package (JEDEC MO-229) All Dimensions in millimeters © 2010 Exar Corporation 14/16 Rev. 2.1.0 SP7686/SP7686A Constant Current Flash Driver in DFN 2mm x 3mm PACKAGE SPECIFICATION 2X3MM DFN © 2010 Exar Corporation 15/16 Rev. 2.1.0 SP7686/SP7686A Constant Current Flash Driver in DFN 2mm x 3mm REVISION HISTORY Revision Date Description 2.0.0 02/20/2010 Datasheet re-write into new format. Previous Revision was P under Sipex logo. Added changes reflected in PCN#10-0201-01 2.1.0 02/26/2010 Fixed resistor values in figure 1 (typical application diagrams) Swapped labels on figures 13 and 14 FOR FURTHER ASSISTANCE Email: customersupport@exar.com Exar Technical Documentation: 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. or its in all Reproduction, in part or whole, without the prior written consent of EXAR Corporation is prohibited. © 2010 Exar Corporation 16/16 Rev. 2.1.0