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SP7618 Datasheet(PDF) 7 Page - Sipex Corporation |
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SP7618 Datasheet(HTML) 7 Page - Sipex Corporation |
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7 / 10 page  7 Date: Dec 5-06 Rev E Constant Current LED Driver © 2006 Sipex Corporation Output Driver The SP768 features a low-side regulated outputcurrentdriver. AlargeMOSFETdevice is connected between the LED and GNDP pins. The MOSFET drain is connected to the LED pins and the MOSFET source is connected to the GNDP pins. There are two pins on each terminal of the MOSFET in order to minimize power dissipation inside the package. Even though there are two LED and GNDP pins, there is actually only one output intended to drive one LED. The light emitting diode connects from VCC to the LED pins. The Iled current regulation is guaranteed at dropout at the LED pins to be less than 00mV. The output current is regulated to within five percent of nominal value even if the voltage between the LED and GNDP pins varies over a wide range. Thenominaloutputisguaranteedwithin±8% of the defined current. Thermal Protection The SP768 has built-in thermal protection. An internal p-n junction is compared to the in- ternal temperature compensated reference. Whenthep-njunctionreachesatemperature specific voltage, it trips a comparator which shutsdownthedriverstageofthepartplacing the device into sleep mode while DAC circuit remains active. The shutdown temperature is defined to be 160°C. Thecomparatorcircuithasbuilt-inhysteresis corresponding to 25°C. The output stage will resume operation and start sinking the cur- rent that was defined prior to shutdown when theinternaltemperaturedropsby25°C. Ifthe part remains in a high ambient temperature environment or if a high power dissipation condition exists, the output stage will cycle on and off to maintain a preset internal junction temperature to avoid catastrophic damage. In that case,the LED will appear to be blinking. Lower the LED voltage to avoid excess power dissipation in the IC. Shutdown The SP768 has a low current shutdown function. In shutdown mode, the part draws less than 0.µA current maximum. The part can be placed into shutdown using the EN pin. ENABLEandCTRLpinscannotbetri-stated or left floating. There are no predefined in- ternal states, so leaving these pins open will cause the part to operate incorrectly. Timeout A Time Duration Before Shutdown feature actsasafailsafetoprotecttheLEDfromlong ON times. The nominal timeout is defined as 4 seconds. Power-on-Reset This function is used to set DAC and Time Duration counters into their initial state after power up. No signal applied to the CTRL pin can be accepted during this time, even if the input voltage is applied simultaneously to Vcc and ENABLE pins. THEORY OF OPERATION |
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