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TPS61163AYFFR Datasheet(PDF) 9 Page - Texas Instruments |
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TPS61163AYFFR Datasheet(HTML) 9 Page - Texas Instruments |
9 / 35 page TPS61162A, TPS61163A www.ti.com SLVSC26A – NOVEMBER 2013 – REVISED JUNE 2015 7.3 Feature Description 7.3.1 Boost Converter The boost converter of the TPS61162A, TPS61163A integrates a 1.5-A, 40-V low-side switch MOSFET and has a fixed switching frequency of 1.2 MHz. The control architecture is based on traditional current-mode Pulse Width Modulation (PWM) control. For operation see the Functional Block Diagram. Two current sinks regulate the dual- channel current, and the boost output is automatically set by regulating voltage on the IFBx pin. The output of error amplifier and the sensed current of switch MOSFET are applied to a control comparator to generate the boost switching duty cycle; slope compensation is added to the current signal to allow stable operation for duty cycles larger than 50%. The forward voltages of two LED strings are normally different due to the LED diode forward voltage inconsistency; thus, the IFB1 and IFB2 voltages are normally different. The TPS61162A, TPS61163A can select out the IFBx pin which has a lower voltage than the other and regulate its voltage to a very low value (90 mV typical), which is enough for the two current sinks' headroom. In this way, the output voltage of the boost converter is automatically set and adaptive to LED strings' forward voltages, and the power dissipation of the current sink regulators can be reduced remarkably with this very low headroom voltage. In order to improve the boost efficiency at light load, Pulse Frequency Modulation (PFM) mode is automatically enabled under light load conditions. When the load current decreases along with the dimming duty, the output of gm amplifier — COMP pin voltage decreases until it is clamped at an internal reference voltage. Because COMP pin voltage controls the inductor peak current, when it is clamped the inductor peak current is also clamped and cannot decrease. As a result, more energy than needed is transferred to the output stage, and the output voltage and IFBx pin voltage increase. An internal hysteresis comparator detects the minimum IFBx pin voltage. When the minimum IFBx voltage is detected as higher than the regulation voltage 90 mV by around 120 mV, the boost stops switching. Then the output voltage, as well as IFBx pin voltage, decrease. When the minimum IFBx voltage is lower than the hysteresis (around 40 mV), the boost switches again. Thus, during PFM mode the boost output trips between the low and high thresholds. When the load increases along with the dimming duty, the COMP pin voltage will exit from the clamped status, and the boost will exit the PFM mode and return to the PWM operation, during which the minimum IFBx pin voltage is regulated at 90 mV again. Refer to Figure 23 and Figure 24 for PFM mode operation. 7.3.2 IFBx Pin Unused If only one channel is needed, a user can easily disable the unused channel by connecting its IFBx pin to ground. If both IFBx pins are connected to ground, the device will not start up. 7.3.3 Enable and Start-up In order to enable the device from shutdown mode, three conditions have to be met: 1. POR (Power On Reset, that is, VIN voltage is higher than UVLO threshold); 2. Logic high on EN pin; and 3. PWM signal (logic high or PWM pulses) on PWM pin. When these conditions are all met, an internal LDO linear regulator is enabled to provide supply to internal circuits and the device can start up. The TPS61162A, TPS61163A support two dimming interfaces: one-wire digital interface (EasyScale interface) and PWM interface. TPS61162A, TPS61163A begin an EasyScale detection window after start-up to detect which interface is selected. If the EasyScale interface is needed, signals of a specific pattern should be input into EN pin during the EasyScale detection window; otherwise, PWM dimming interface will be enabled (see details in One-Wire Digital Interface (EasyScale Interface)). After the EasyScale detection window, the TPS61162A, TPS61163A check the status of IFBx pins. If one IFBx pin is detected to connect to ground, the corresponding channel will be disabled and removed from the control loop. Then the soft-start begins, and the boost converter starts switching. If both IFBx pins are shorted to ground, the TPS61162A, TPS61163A will not start up. Either pulling EN pin low for more than 2.5 ms or pulling PWM pin low for more than 20 ms can disable the device, and the TPS61162A, TPS61163A enters into shutdown mode. Copyright © 2013–2015, Texas Instruments Incorporated Submit Documentation Feedback 9 Product Folder Links: TPS61162A TPS61163A |
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