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TPS61236PRWLT Datasheet(PDF) 10 Page - Texas Instruments |
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TPS61236PRWLT Datasheet(HTML) 10 Page - Texas Instruments |
10 / 38 page PWM mode at heavy load PFM mode at light load Output Voltage t VOUT_NOM VOUT_PFM one PFM cycle Inductor Current IVALLEY ton fsw IPEAK (loop controlled) ¨,L 10 TPS61235P, TPS61236P SLVSCK4A – SEPTEMBER 2015 – REVISED MAY 2016 www.ti.com Product Folder Links: TPS61235P TPS61236P Submit Documentation Feedback Copyright © 2015–2016, Texas Instruments Incorporated 8.3 Feature Description 8.3.1 Boost Controller Operation The TPS6123x synchronous boost converter typically operates at a quasi-constant 1-MHz frequency Pulse Width Modulation (PWM) at moderate to heavy load, which allows the use of small inductors and capacitors to achieve a small solution size. At light load, it operates in power-save mode with Pulse Frequency Modulation (PFM) for improved efficiency. During PWM operation, the converter uses a quasi-constant on-time valley current mode control scheme to achieve excellent line/load regulation. Based on the VIN /VOUT ratio, a simple circuit predicts the required on-time. At the beginning of the switching cycle, the low-side NMOS switch is turned on and the inductor current ramps up to a peak current that is determined by the on-time and the inductance. Once the on-time has expired, the low- side switch is turned off and the rectifying NMOS switch is turned on. The inductor current decays until reaching the valley current threshold which is determined by internal control loops. Once this occurs, the on-time is set again to turn the low-side switch back on and the cycle is repeated. Internal loop compensation is implemented to simplify the design process while minimizing the number of external components. A bootstrap circuit is built in to drive the rectifying NMOS switch. Figure 13 illustrates the PWM mode operation. Figure 13. PWM Mode Operation Illustration Under a light load condition, the converter works in Pulse Frequency Modulation (PFM) mode. In this mode, the boost converter switches and ramps up the output voltage until VOUT reaches the PFM threshold. Then it stops switching and consumes less quiescent current. It resumes switching when the output voltage drops below the threshold. The converter exits PFM mode when the output current can no longer be supported in this mode. Refer to Figure 14 for PFM mode operation details. Figure 14. PFM Mode Operation Illustration 8.3.2 Soft Start The TPS6123x integrates an internal soft start circuit which controls ramp up of the output voltage and prevents the converter from inrush current during start-up. When the device is enabled, the rectifying switch is turned on to charge the output capacitor to the input voltage. This is called the pre-charge phase. During the phase, the output current is limited to the pre-charge current limit ILIM_pre, which is proportional to the output voltage. The pre-charge current increases when the output voltage gets higher. |
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