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TPS92690-Q1 Datasheet(PDF) 10 Page - Texas Instruments |
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TPS92690-Q1 Datasheet(HTML) 10 Page - Texas Instruments |
10 / 41 page O V O IN nV D nV = + O O IN V D V V = + O IN O V V D V - = Time tON = D×tS . IL(min) 0 tOFF = (1±D)×tS tS . IL(max) 'iL(P-P) iL TPS92690-Q1 SLVSCU0 – NOVEMBER 2015 www.ti.com 7.3 Feature Description 7.3.1 Current Regulators Current regulators can be designed to accomplish different functions: boost, buck-boost, and flyback. The TPS92690-Q1 device is designed to drive a ground referenced N-channel FET and sense a ground referenced LED load. This control architecture is perfect for driving boost, SEPIC, flyback, or Cuk topologies. It does not work with a floating buck or buck-boost topology since the LED current sense amplifier is ground referenced. Looking at the boost design in the Typical Boost Application, the basic operation of a current regulator can be analyzed. During the time that the N-channel FET (Q1) is turned on (tON), the input voltage source stores energy in the inductor (L1) while the output capacitor (CO) provides energy to the LED load. When Q1 is turned off (tOFF), the re-circulating diode (D1) becomes forward biased and L1 provides energy to both CO and the LED load. Figure 11 shows the inductor current (iL(t)) waveform for a regulator operating in CCM. Figure 11. Basic CCM Inductor Current Waveform The average output LED current (ILED) is proportional to the average inductor current (IL), therefore if IL is tightly controlled, ILED is well regulated. As the system changes input voltage or output voltage, the ideal duty cycle (D) is varied to regulate IL and ultimately ILED. For any current regulator, D is a function of the conversion ratio: Use Equation 1 to calculate the duty cycle for an application using the boost topology. (1) Use Equation 2 to calculate the duty cycle for an application using the buck-boost (SEPIC/Cuk) topology. (2) Use Equation 3 to calculate the duty cycle for an application using the flyback topology. where • n is the primary to secondary turns ratio of the coupled inductor, n:1 (3) 7.3.2 Peak Current Mode Control Peak current mode control is used by the TPS92690-Q1 device to regulate the average LED current through an array of HBLEDs. This method of control uses a series resistor in the LED path to sense LED current and can use either a series resistor in the MOSFET path or the MOSFET RDS(on) for both cycle-by-cycle current limit and input voltage feed forward. The controller has a fixed switching frequency set by an internal programmable oscillator therefore slope compensation is added to mitigate current mode instability. A detailed explanation of this control method is presented in the following sections. 10 Submit Documentation Feedback Copyright © 2015, Texas Instruments Incorporated Product Folder Links: TPS92690-Q1 |
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