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TLC5921 Fiches technique(PDF) 9 Page - Texas Instruments |
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TLC5921 Fiches technique(HTML) 9 Page - Texas Instruments |
9 / 14 page TLC5921 LED DRIVER SLLS390 – SEPTEMBER 1999 9 POST OFFICE BOX 655303 • DALLAS, TEXAS 75265 PRINCIPLES OF OPERATION LOD function (LED open detection) If any terminal voltage of constant current output (OUT0 TO 15) to be turned on is approximately below 0.3 V, XDOWN output goes low during output on by knowing LED disconnection. This function is operational for sixteen OUTn individually. To know which constant current output is disconnected, the level of XDOWN is repeatedly checked 16 times from OUT0 to OUT15 turning one constant current output on. The power supply voltage for LED should be set to that the constant current output is applied to above 0.4 V to prevent from XDOWN low when LED is lighting on normally. Note that on-time should be minimum1 µs after the constant current output is turned on since XDOWN output is required approximately 1 µs. As discussed earlier, XDOWN is used for both TSD and LOD function. Therefore, BLANK is used to know which one of TSD or LOD worked when XDOWN went low at LED disconnection, that is, in this condition, when set BLANK to high, all the constant current outputs are turned off and LOD disconnection detection is disabled, then, if XDOWN was changed to high, LED disconnection must be occurred. Table 1 is an example for XDOWN output status using four LEDs. Table 1. XDOWN Output Example LED NUMBER 1 2 3 4 LED STATUS GOOD NG GOOD NG OUTn ON ON ON ON DETECTION RESULT GOOD NG GOOD NG XDOWN LOW (by case 2, 4) LED NUMBER 1 2 3 4 LED STATUS GOOD NG GOOD NG OUTn ON ON OFF OFF DETECTION RESULT GOOD NG GOOD GOOD XDOWN LOW (by case 2) LED NUMBER 1 2 3 4 LED STATUS GOOD NG GOOD NG OUTn OFF OFF OFF OFF DETECTION RESULT GOOD GOOD GOOD GOOD XDOWN2 HIGH–IMPEDANCE noise reduction : output slope When output current is 80 mA, the time to change constant current output to turn-on and turn-off is approximately 150 ns and 250 ns respectively. This allows to reduce concurrent switching noise occurred when multiple outputs turn or off at the same time. thermal pad The thermal pad should be connected to GND to eliminate the noise influence since it is connected to the bottom side of IC chip. Also, desired thermal effect will be obtained by connecting this pad to the PCB pattern with better thermal conductivity. |
Numéro de pièce similaire - TLC5921 |
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Description similaire - TLC5921 |
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