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TPS92411P Fiches technique(PDF) 8 Page - Texas Instruments |
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TPS92411P Fiches technique(HTML) 8 Page - Texas Instruments |
8 / 22 page ( ) - ´ ´ = + LED SNS RSET VS V 1.24 V 2 R R V 0.21V + = SNS SNS RSNS V 0.21V R I TPS92411, TPS92411P SLUSBQ6 – OCTOBER 2013 www.ti.com APPLICATION INFORMATION APPLICATION The TPS92411 is an advanced, floating driver specifically designed for use with a linear regulator in low-power offline LED lighting applications. It integrates an on-board 100-V MOSFET switch to shunt LED current as the line transitions. As the line transitions through the cycle, the device monitors critical nodes for zero cross at which time the internal switch is either opened or shorted to steer the current through or away from the LED stack. The device determines the output power by setting the average of the combined LED currents throughout the line cycle using the linear regulator. SETTING THE SWITCHING THRESHOLDS (RSNS, RSET) The TPS92411 features two threshold settings to allow for proper LED control. The first setting determines when the internal switch turns off and allows current to charge the capacitor and flow through the LEDs. The second setting determines when the switch turns on to shunt the LEDs and allow the capacitor to supply current. The lower switch turn-on threshold (VSNS) should be set first using a resistor (RRSNS) from the RSNS pin to system ground. For best efficiency set this threshold between 4 V and 6 V. Then the upper switch turn-off threshold (VVS) can be set using a resistor (RRSET) from the RSET pin to the VIN pin. Set this threshold approximately 6 V to 10 V above the LED stack voltage (VLED). The RSET threshold should be greater than the LED stack voltage plus the value of the RSNS threshold to prevent errant switching. These thresholds can be set with resistance calculated using Equation 1 and Equation 2 (1) (2) OVERVOLTAGE PROTECTION (OVP) Overvoltage protection (OVP) in the TPS92411P version protects the device as well as the LEDs and storage capacitor. The OVP is set at approximately 100 V (VVIN – VVS) and closes the internal switch when the threshold voltage is reached. For this reason LED stack voltages of 94 V or less are recommended. Higher voltages can be used with the TPS92411 version but tolerances must be considered to ensure that the 105 V absolute maximum rating is not exceeded. INPUT UNDERVOLTAGE LOCKOUT (UVLO) The TPS92411 includes input UVLO. The UVLO prevents the device from operation until the VIN pin voltage with respect to VS exceeds 6.5 V and ensures the device behaves properly when enabled. LED CAPACITOR A capacitor is required across each LED stack to provide current to the LEDs during the switch ON time. Refer to the available calculator software (SLVC516 for 120-V applications or SLVC517 for 230-V applications) for calculating the minimum value required for any particular application. The software calculates the minimum value required for a particular application, but best performance is acheived by using as much capacitance as possible given size and cost constraints. These design tools also calculate a minimum value for any given current ripple percent or flicker index desired for the particular application. BLOCKING DIODE A blocking diode is required between the drain of the switch (DRAIN) and the anode of the LED stack. This prevents the LED capacitor from discharging through the switch during the switch ON time instead allowing it to discharge through the LED stack. This diode should be rated for 200 V reverse voltage and capable of forward currents as high as the average linear regulator current setting. 8 Submit Documentation Feedback Copyright © 2013, Texas Instruments Incorporated Product Folder Links: TPS92411 TPS92411P |
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