LM3102, LM3102-Q1

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SNVS515H – SEPTEMBER 2007 – REVISED JUNE 2015

7 Detailed Description

7.1 Overview

The LM3102/-Q1 Step-Down Switching Regulator features all required functions to implement a cost-effective,

efficient buck power converter capable of supplying 2.5 A to a load. It contains Dual N-channel main and

synchronous MOSFETs. The Constant ON-Time (COT) regulation scheme requires no loop compensation,

results in fast load transient response and simple circuit implementation. The regulator can function properly

even with an all ceramic output capacitor network, and does not rely on the ESR of the output capacitor for

stability. The operating frequency remains constant with line variations due to the inverse relationship between

the input voltage and the ON-time. The valley current limit detection circuit, with the limit set internally at 2.7 A,

inhibits the main MOSFET until the inductor current level subsides.

The LM3102/-Q1 can be applied in numerous applications and can operate efficiently for inputs as high as 42 V.

LM3102/-Q1 is available in the thermally enhanced HTSSOP-20 package.

7.2 Functional Block Diagram

7.3 Feature Description

7.3.1 COT Control Circuit Overview

COT control is based on a comparator and a one-shot ON-timer, with the output voltage feedback (feeding to the

FB pin) compared with an internal reference of 0.8 V. If the voltage of the FB pin is below the reference, the main

upon which the ON-time varies inversely. Following the ON-time, the main MOSFET remains off for a minimum

of 260 ns. Then, if the voltage of the FB pin is below the reference, the main MOSFET is turned on again for

another ON-time period. The switching will continue to achieve regulation.

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Product Folder Links: LM3102 LM3102-Q1