PDF SP7686A Data sheet ( Hoja de datos )

Número de pieza	SP7686A
Descripción	Constant Current Flash Driver
Fabricantes	Sipex Corporation
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No Preview Available ! www.DataSheet4U.com Solved by SP7686/7686A TM Constant Current Flash Driver in DFN 2mm x 3mm FEATURES SP7686 SP7686A 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 (<150µs) 3.5s Timeout function to protect the LED Thermal shutdown protection Built-in over-voltage and over-current protection Fixed output versions available (SP7686A) Automatic soft start limits in-rush current Lead Free, RoHS Compliant Package: Space saving 8-pin 2x3mm DFN DESCRIPTION The SP7686 is a current regulated charge pump ideal for powering 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 over-voltage, over- current, over-temperature and FLASH time-out protection features. The SP7686 is offered in the 2x3mm 8-pin DFN package. TYPICAL APPLICATION CIRCUITS 0.22uF VIN 10uF CTRL VIN C1 C2 SCP2 7686 CTRL FB PGND SGND SGND 2.2uF 500mA 0.68Ω 0.22uF VIN 10uF FLASH EN VIN C1 C2 C2 SP7686A FLAS EN PGND FB 2.2uF 500mA 0.33Ω Jul16-07 RevP SP7686: 500mA LED Driver -1-  2007 Sipex Corporation 1 page www.DataSheet4U.com 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 THEORY OF OPERATION 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 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. Overvoltage Protection 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. Jul16-07 RevP SP7686: 500mA LED Driver -5-  2007 Sipex Corporation 5 Page www.DataSheet4U.com 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 APPLICATION INFORMATION 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 - 11 -  2007 Sipex Corporation 11 Page

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