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XRP7618 Datasheet(PDF) 6 Page - Exar Corporation |
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XRP7618 Datasheet(HTML) 6 Page - Exar Corporation |
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6 / 10 page  X XR RP P7 76 61 18 8 8 8--C Ch ha an nn ne ell C Co on ns stta an ntt C Cu urrrre en ntt L Liin ne ea arr L LE ED D D Drriiv ve err W Wiitth h S Sm ma arrtt T Ta allk kTTM M © 2011 Exar Corporation 6/10 Rev. 1.0.0 THEORY OF OPERATION The XRP7618 is an eight channel programmable constant current LED driver capable of up to 100mA per channel. A single external resistor adjusts the current for each channel over a 10mA to 100mA range with tight matching between channels. Dimming is supported through a standard PWM scheme or through an analog signal. Furthermore, the XRP7618 maximizes the overall system efficiency by dynamically reporting the minimum LED voltage necessary to remain in current regulation mode when used with a boost converter. Multiple XRP7618s can be placed in parallel to drive over 8 strings of LEDs; however, unused channels should be tied to ground. Built-in under voltage lock out, open LED and over temperature protections insure safe operations under abnormal operating conditions. LED CHANNELS CURRENT SETTING The maximum LED current can be set up to 100mA per channel through the ISET pin. To set the reference current ISET, connect a resistor RSET between this pin and ground. The value of RSET can be calculated by the following formula: 1.194 This reference current is multiplied internally with a gain (K) of 400 then mirrored on all enabled channels. This sets the maximum LED current, referred to as 100% current (ILEDMAX). The value can be calculated by the following formula: or, 1.194 400 1.194 The LED current can be reduced from 100% by PWM dimming control. PWM DIMMING CONTROL The LED current can be adjusted by applying a PWM signal to the PWM pin. In this mode, all enabled channels are adjusted at the same time and brightness is adjusted from 1% to 100% of ILEDMAX. The supported external PWM signal frequency is 100Hz to 25kHz. ANALOG DIMMING CONTROL Besides PWM dimming control, the LED current can be controlled continuously (from highest to lowest LED current) by raising the voltage at the bottom of RSET from 0V normally to 1V max, respectively. RSET value may be determined as 1.194 400 where, 1.194V is a typical ISET pin voltage, VMOD is an adjustment voltage applied to the bottom side of RSET, 400 is the typical current multiplication ratio, and ILEDMAX is the required LED current per channel. Fig. 10: XRP7618 Analog Dimming Control If adjustment voltage VMOD isn’t used, RSET resistor should be connected to ground. SYSTEM POWER OPTIMIZATION The Smart Talk feature enables XRP7618 to maximize the overall system power efficiency, when used with a step-up converter, by dynamically reporting the minimum LED channel voltage needed to maintain current regulation mode. The XRP7618 samples the voltage on each channel input and reports the lowest voltage of all strings via the FB signal to the associated step up converter. If placed in shutdown through the EN pin or if all channels are inactive, the XRP7618 outputs |
Similar Part No. - XRP7618 |
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Similar Description - XRP7618 |
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