Sp6648 Flashlight Application

Posted on Feb 5, 2014

The Infrared (IR) LED used in a remote control is an application for an LED Driver that has specific requirements that may exceed the requirements for a typical LED driver application. For this application, the IR LED driver will run off a 9V alkaline battery, which has a range of voltage from 5. 7V to 9. 6V, which is a higher voltage range than typ

Sp6648 Flashlight Application
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ical portable devices. The next requirement is for the frequency of the PWM signal to go as high as 100kHz, which is much higher than the typical PWM frequency of 100Hz. Lastly, the Turn-on and Turn-off time for the IR LED driver need to be less than 1 µsec, while in a typical LED application this CAN be more than 100 µsec. The SP6691 switching Regulator used in this application is typically used as a non-synchronous boost for voltage output or for driving LEDs with a current regulation controlled by the FB pin. In this application, the SP6691 is used in a different configuration to drive an IR LED that CAN be used for a remote control with pulses as fast as 100kHz. To implement such a high frequency, the typical method of controlling the SP6691 with pulses to the EN pin would not be fast enough since the EN pin CAN take about 50 to 100 µsec to begin to turn on the SP6691 output (see figure 1). Another consideration for the SP6691 would be that it is typically a boost Regulator while in this application the input voltage is from a 9V alkaline battery which CAN range from 5. 7V to 9. 6V and the output is an IR LED which needs less than 2. 0V.

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