LT3840 operaTion OVERVIEW The external y compensated VC voltage generates a The LT3840 provides a solution for a high efficiency, general threshold for the differential current sense comparator. purpose DC/DC converter. It is a wide input voltage range During normal operation, the LT3840 internal oscillator switching regulator controller IC that uses a program- runs at the programmed frequency. At the beginning of mable fixed frequency, peak current mode architecture. each oscillator cycle, the TG switch drive is turned on. The An internal switching regulator efficiently provides an TG switch drive stays enabled until the sensed inductor auxiliary bias supply to drive multiple, large N-channel current exceeds the VC derived threshold of the current MOSFET switches. sense comparator. The LT3840 includes functions such as average output If the current comparator threshold is not reached for the current control and monitoring, micro-power operation entire oscillator cycle, the switch driver stays on for up with low output ripple, soft-start, output voltage tracking, to eight cycles. If after eight cycles the TG switch driver power good and a handful of protection features. is still on, it is turned off to regenerate the BOOST boot- strapped supply. Voltage Control Loop When the load current increases, the FB voltage decreases The LT3840 uses peak current mode control to regulate relative to the reference causing the EA to increase the VC the supply output voltage. The error amplifier (EA) gener- voltage until the average inductor current matches the new ates an error voltage (V load current. Refer to Figure 1 for a block diagram of the C) based on the difference between the feedback (FB) voltage and an internal reference. LT3840 voltage control loop. BOOST VIN INTVCC TG DRIVER EXTERNAL COMPONENTS SW ANTI SHOOT VOUT THRU INTVCCDRIVER BG BGRTN Q S R OSCILLATOR SENSE+ + SYNC RT SENSE– – FB – VC EA + VREF 3840 BD Figure 1. Peak Current Mode Voltage Control Functional Block Diagram 3840fa For more information www.linear.com/LT3840 9 Document Outline Features Description Applications Typical Application Absolute Maximum Ratings Pin Configuration Order Information Electrical Characteristics Typical Performance Characteristics Pin Functions Operation Applications Information Typical Applications Package Description Revision History Typical Application Related Parts
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