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TPS6229x-Q1 Fiches technique(PDF) 9 Page - Texas Instruments |
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TPS6229x-Q1 Fiches technique(HTML) 9 Page - Texas Instruments |
9 / 27 page Outputvoltage Vout (PWM) Vout +1% PFMComparator threshold VoltagePositioning Lightload PFMMode moderatetoheavyload PWMMode 9 TPS62290-Q1, TPS62293-Q1 www.ti.com SLVSAI5B – SEPTEMBER 2010 – REVISED JUNE 2016 Product Folder Links: TPS62290-Q1 TPS62293-Q1 Submit Documentation Feedback Copyright © 2010–2016, Texas Instruments Incorporated 8.3 Feature Description 8.3.1 Power Save Mode The Power Save Mode is enabled with MODE Pin set to low level. If the load current decreases, the converter enters Power Save Mode operation automatically. During Power Save Mode, the converter skips switching and operates with reduced frequency in PFM mode with a minimum quiescent current to maintain high efficiency. The converter positions the output voltage typically +1% above the nominal output voltage. This voltage positioning feature minimizes voltage drops caused by a sudden load step. The transition from PWM mode to PFM mode occurs once the inductor current in the low-side MOSFET switch becomes zero, which indicates discontinuous conduction mode. During the Power Save Mode the output voltage is monitored with a PFM comparator. As the output voltage falls below the PFM comparator threshold of VOUT nominal +1%, the device starts a PFM current pulse. For this the high-side MOSFET switch turns on and the inductor current ramps up. After the ON-time expires, the switch is turned off, and the low-side MOSFET switch is turned on until the inductor current becomes zero. The converter effectively delivers a current to the output capacitor and the load. If the load is below the delivered current, the output voltage rises. If the output voltage is equal or higher than the PFM comparator threshold, the device stops switching and enters a sleep mode with typical 15-µA current consumption. If the output voltage is still below the PFM comparator threshold, a sequence of further PFM current pulses are generated until the PFM comparator threshold is reached. The converter starts switching again once the output voltage drops below the PFM comparator threshold. With a fast single-threshold comparator, the output voltage ripple during PFM mode operation can be kept small. The PFM Pulse is time controlled, which allows modification of the charge transferred to the output capacitor by the value of the inductor. The resulting PFM output voltage ripple and PFM frequency depend in first order on the size of the output capacitor and the inductor value. Increasing output capacitor values and inductor values minimizes the output ripple. The PFM frequency decreases with smaller inductor values and increases with larger values. The PFM mode is left and PWM mode entered in case the output current can not longer be supported in PFM mode. The Power Save Mode can be disabled through the MODE pin set to high. The converter then operates in fixed frequency PWM mode. 8.3.1.1 Dynamic Voltage Positioning This feature reduces the voltage undershoots and overshoots at load steps from light to heavy load and vice versa. It is active in Power Save Mode and regulates the output voltage 1% higher than the nominal value. This provides more headroom for both the voltage drop at a load step, and the voltage increase at a load throw-off. Figure 6. Power Save Mode Operation 8.3.1.2 100% Duty Cycle Low Dropout Operation The device starts to enter 100% duty cycle Mode once the input voltage comes close the nominal output voltage. To maintain the output voltage, the high-side MOSFET switch is turned on 100% for one or more cycles. |
Numéro de pièce similaire - TPS6229x-Q1 |
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