TL3845DRG4

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TL3845DRG4 Application Field and Working Principle
The TL3845DRG4 is a high speed, BiCMOS, controlled on-time buck regulatorcontroller, supplied in a thermally enhanced 4mm x 4mm 16-pin PowerQFNpackage. It is part of now’s voltage regulators, DC DC switching controllerscategory, specially tailored to drive up high efficiency power conversionapplications, such as notebook adapter and telecom server supplies.

The device operates over a wide input range of 8V to 40V, and is capableof delivering up to 8A of continuous load current. It is designed to haveexcellent line and load regulation, feeding an external power MOSFET.The device incorporates the features needed to control either alone or multiphase operation converters.

The TL3845DRG4 contains the features needed to control either singleor multiphase operation converters. The output voltage is programmedusing a single external resistor, employing the simplest possible designfor controlling the output voltage. It features a low-dropout currentlimit amplifier for constant output current up to 8A during normaloperation and high-speed overcurrent protection. It is also suppliedwith an open loop power limiter, which ensures reliable protectionagainst over temperature.

The TL3845DRG4 utilizes a voltage mode architecture and fuses a500kHz fixed frequency control scheme. A PWM comparator is includedto allow the selection of two options to control the output voltage:pulse-by-pulse current-limit or voltage-mode control. The switchingfrequency can be internally programmed to five different values (400kHz,500kHz, 600kHz, 800kHz and 1MHz) by simply connecting a single resistorbetween the SSON (Soft-Start On) pin and ground. It also offers alow-ripple Burst Mode® operation with excellent light-load efficiencydue to the fast operation of the PWM comparator.

In operation, the TL3845DRG4 integrates a low-dropout (LDO) currentlimit amplifier that senses the output voltage and outputs an appropriatedrive signal to the power MOSFETs. The output voltage will be programmedvia a single external resistor, between the FB pin and ground. The outputvoltage is regulated by varying the internal voltage references to adjustthe duty cycle. The PWM comparator controls the on-time after the outputvoltage through the error amplifier. A soft-start capacitor is also connectedto the SS pin, which determines the time taken by the controller toregulate the output voltage.

The TL3845DRG4 also features a programmable over-voltage protection (OVP)with hysteresis. When the sense voltage exceeds the OVP threshold,the device enters the current limit. The OVP level is set by connectingthe OVP pin either to VCC or an external voltage reference appropriatefor the output voltage.

The TL3845DRG4 includes several protections such as short-circuit,over-current, and over-temperature protections to prevent potentialdamages to the system. The device also has an on-chip current-senseamplifier, which provides a fast and robust control loop. The integratedprotection functions are programmable via external resistors, so theexternal power MOSFETs are protected against destructive damages.

In summary, the TL3845DRG4 is designed to provide a high efficient,high power density, cost-effective solution for power delivery in variousapplications. It features excellent line and load regulation, enablingthe device to be used for high speed buck converter with fast transientresponse. It also offers exceptional protection functions, and allowsthe user to select the desired switching frequency. Therefore, theTL3845DRG4 is a solid choice for applications requiring a high efficiency,high performance, and compact power converter.

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