SP7686AER-L

Solved by SP7686/7686A TM Constant Current Flash Driver in DFN 2mm x 3mm FEATURES Output current up to 500mA Up to 94% efficiency in 1x mode Built-in LED current setting DAC One line serial interface 2.4MHz switching frequency FB Reference voltage adjusts in 10mV steps from 60mV to 360mV DAC signal shutdown control Power-saving shutdown mode of 10nA PWM brightness control for DAC Fast turn-on ( 350µsec, VEN < 0.4V (SP7686A) VFB = 0mV, DAC=00000 ♦ mV mV mV mV ♦ ♦ ♦ ♦ ♦ ♦ % mV mV µA MHz 60mV< VFB120mV (adj version 11 CTRL pulses), FLASH= high (fixed version) Driver shutdown Driver enabled (EN pin is SP7686A only) st 0.5 ♦ ♦ µs µs µs µs ♦ ♦ ♦ ♦ ♦ µs s V V µA Note 1: Guaranteed maximum allowable power dissipation depends on the ambient temperature. Jul16-07 RevP SP7686: 500mA LED Driver  2007 Sipex Corporation -2- PIN DESCRIPTION PIN # 1 2, 3 PIN NAME VIN C1, C2 SP7686 PIN 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 CTRL 5 6 7 8 FB SGND PGND VOUT PIN # 1 2, 3 PIN NAME VIN C1, C2 SP7686A PIN DESCRIPTION Power supply input. Place a 10µF decoupling capacitor next to this pin. Connect an external 0.22µF flying capacitor between these pins 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 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). The fixed current driver (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. 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 FLASH 5 FB 6 7 8 EN PGND VOUT Jul16-07 RevP SP7686: 500mA LED Driver  2007 Sipex Corporation -3- SP7686 FUNCTIONAL DIAGRAM SP7686A FUNCTIONAL DIAGRAM Jul16-07 RevP SP7686: 500mA LED Driver  2007 Sipex Corporation -4- THEORY OF OPERATION 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. SP7686A 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 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: 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 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. 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. 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. 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. Overtemperature Protection W hen 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. Overvoltage Protection Jul16-07 RevP SP7686: 500mA LED Driver  2007 Sipex Corporation -5- TIMING DIAGRAM S (Not to Scale) VIN POR TPOR < 600us TDELAY < 75us TS < 50us TOFFC = 200us TON < 200us CTRL VFB Timing Diagram for SP7686 VIN POR TPOR < 600us FLASH TS < 50us TON < 200us ILED TOFF < 50us ENABLE Timing Diagram for SP7686A Jul16-07 RevP SP7686: 500mA LED Driver  2007 Sipex Corporation -6- TYPICAL PERFORMANCE CHARACTERISTICS VIN = 3.6V, Typical Application Circuit, D1 = Luxeon LXCL-PWF3, Ta = 25C unless otherwise noted. VFB vs Vctrl Pulse 400 350 300 VFB (mV) 250 200 150 100 50 0 3 6 9 12 15 18 Vctrl Pulse 21 24 27 30 33 Vin=4.2V Vin=3.6V Vin=3.0V Figure 1. SP7686 VFB Vs VCTRL Pulses Iout vs Vctrl Pulse 550 500 450 400 350 300 250 200 150 100 50 0 3 6 9 12 15 18 21 24 Iout (mA) Vin=4.2V Vin=3.6V Vin=3.0V 27 30 33 Vctrl Pulse Figure 2. SP7686 IOUT Vs VCTRL Pulses 500 400 Iout (mA) 300 200 100 0 3.0 3.3 3.6 Vin (V) 3.9 4.2 Flash 440mA Torch 160mA Torch 88mA 100 90 80 70 60 50 40 30 20 10 0 3.0 3.3 3.6 Vin (V) Efficiency (%) Flash 440mA Torch 160mA Torch 88mA 3.9 4.2 Figure 3. SP7686 Output Current Vs Input Voltage Figure 4. SP7686 Efficiency Jul16-07 RevP SP7686: 500mA LED Driver  2007 Sipex Corporation -7- TYPICAL PERFORMANCE CHARACTERISTICS VIN = 3.6V, Typical Application Circuit, D1 = Luxeon LXCL-PWF3, TA = 25˚C unless otherwise noted. CTRL CTRL VOUT VOUT VFB VIN=4.2V VFB VIN=4.2V IIN: 0.5A/div IIN: 0.5A/div Figure 5. SP7686 Startup with 3 CTRL Pulses Figure 6. SP7686 Startup with 32 CTRL Pulses CTRL CTRL VOUT VOUT VFB VFB IIN: 0.5A/div IIN: 0.5A/div Figure 7. SP7686 Turn-off time into SHDN Figure 8. SP7686 Vout Shorted to GND, VIN = 5.5V CTRL VOUT Efficiency (%) 100 90 80 70 60 50 40 30 VFB Flash 450mA Torch 150mA 2.7 3.0 3.3 Vin (V) IIN: 0.5A/div 3.6 3.9 4.2 Figure 9. SP7686 LED Open, VIN = 4.2V Figure 10. SP7686A Efficiency Jul16-07 RevP SP7686: 500mA LED Driver  2007 Sipex Corporation -8- TYPICAL PERFORMANCE CHARACTERISTICS VIN = 3.6V, Typical Application Circuit, D1 = Luxeon LXCL-PWF3, TA = 25˚C unless otherwise noted. 500 400 Iout (mA) 300 200 100 0 2.7 3.0 3.3 3.6 3.9 4.2 Vin (V) 200 150 Iout (mA) 100 50 0 2.7 3.0 3.3 3.6 3.9 4.2 Vin (V) Figure 11. SP7686A Torch Mode Output Current Figure 12. SP7686A Flash Mode Output Current CTRL VOUT CTRL VOUT VFB VFB Figure 13. SP7686A Turn-off to Shutdown, VIN=4.2V Figure 14. SP7686A Time-out Flash to Shutdown, VIN=4.2V EN VOUT EN VOUT VFB VFB IIN 1A/div IIN 1A/div Figure 15. SP7686A Flash Mode 1X, VIN=4.2V Figure 16. SP7686A Flash Mode 2X, VIN=3.4V Jul16-07 RevP SP7686: 500mA LED Driver  2007 Sipex Corporation -9- TYPICAL PERFORMANCE CHARACTERISTICS VIN = 3.6V, Typical Application Circuit, D1 = Luxeon LXCL-PWF3, TA = 25˚C unless otherwise noted. EN VOUT EN VOUT VFB VFB IIN 0.5A/div IIN 0.5A/div Figure 17. SP7686A Torch Mode 1X, VIN=4.2V Figure 18. SP7686A Torch Mode 2X, VIN=2.9V FLASH FLASH VOUT VOUT VFB VFB Figure 19. SP7686A 1X Torch to 2X Flash, VIN=3.3V Figure 20. SP7686A 2X Flash to 1X Torch, VIN=3.3V VOUT VFB VOUT VFB Figure 21. SP7686A Flash 1X Ripple, VIN=4.2V Figure 22. SP7686A Torch 1X Ripple, VIN=3.0V Jul16-07 RevP SP7686: 500mA LED Driver  2007 Sipex Corporation - 10 - APPLICATION INFORMATION 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. Figure 23. SP7686 with 4 LEDs in parallel Figure 24. SP7686A with 4 LEDs in parallel Jul16-07 RevP SP7686: 500mA LED Driver  2007 Sipex Corporation - 11 - 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. 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. 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 work but input voltage ripple will increase and may effect regulation. APPLICATION INFORMATION (Continued) Resistor Selection for 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 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. Manufacturers/ Website 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 Part Number 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 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 ESR at 100KHz 0.05 0.03 0.03 0.02 0.02 0.05 0.03 0.03 0.02 0.02 Table 1. Capacitor Selection Jul16-07 RevP SP7686: 500mA LED Driver  2007 Sipex Corporation - 12 - APPLICATION INFORMATION (Continued) Part Reference RSENSE RSENSE RSENSE RSENSE RSENSE RSENSE RSENSE Value 0.22ohms 0.27ohms 0.33ohms 0.39ohms 0.47ohms 0.56ohms 0.68ohms Tolerance 1% or 5% 1% or 5% 1% or 5% 1% or 5% 1% or 5% 1% or 5% 1% or 5% Size 0603 0603 0603 0603 0603 0603 0603 Manufacturers Panasonic or Vishay Panasonic or Vishay Panasonic or Vishay Panasonic or Vishay Panasonic or Vishay Panasonic or Vishay Panasonic or Vishay Table 2. Resistor Selection 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 60mV to 360mV in 10mV 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 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 60mV. Subsequent pulses set the feedback voltage in 10mV steps as shown in the Typical Performance Characteristics. Jul16-07 RevP SP7686: 500mA LED Driver  2007 Sipex Corporation - 13 - RECOMMENDED LAYOUT Footprint Drawing: PCB Footprint for 2x3mm 8pin DFN Package (JEDEC MO-229) All Dimensions in millimeters Jul16-07 RevP SP7686: 500mA LED Driver  2007 Sipex Corporation - 14 - PACKAGE DRAWING Jul16-07 RevP SP7686: 500mA LED Driver  2007 Sipex Corporation - 15 - Ordering Information Part Number SP7686AER-L SP7686AER-L/TR SP7686ER-L SP7686ER-L/TR MIN Package RoHS Temp (° C) DFN8 DFN8 DFN8 DFN8 ▪ ▪ ▪ ▪ -40 -40 -40 -40 MAX Temp Status (° C) 85 85 85 85 Active Active Active Active Pack Type / Quantity Bulk Tape & Reel 3000 Bulk Tape & Reel 3000 MSL Level L1 @ 250ºC L1 @ 250ºC L1 @ 250ºC L1 @ 250ºC For further assistance: Email: WWW Support page: Sipex Application Notes: Sipexsupport@sipex.com http://www.sipex.com/content.aspx?p=support http://www.sipex.com/applicationNotes.aspx Solved by TM Sipex Corporation Headquarters and Sales Office 233 South Hillview Drive Milpitas, CA 95035 tel: (408) 934-7500 fax: (408) 935-7600 Sipex Corporation reserves the right to make changes to any products described herein. Sipex 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. Jul16-07 RevP SP7686: 500mA LED Driver  2007 Sipex Corporation - 16 -