S2

S4

S1

S3

1.2-V

Reference

1.7-MHz

Oscillator

OCL

OCL = Overcurrent Limit

VIN

VOUT

C-

C+

Soft-

start

SD

LM2750

GND

FB**

Ra*

Rb*

* LM2750-5.0 only

** LM2750-ADJ only

R1**

R2**

Copyright © 2016, Texas Instruments Incorporated

9

LM2750, LM2750-ADJ

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SNVS180N – APRIL 2002 – REVISED APRIL 2016

Product Folder Links: LM2750 LM2750-ADJ

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Copyright © 2002–2016, Texas Instruments Incorporated

7 Detailed Description

7.1 Overview

The LM2750 is a regulated switched capacitor doubler that, by combining the principles of switched-capacitor

voltage boost and linear regulation, generates a regulated output from an extended Li-Ion input voltage range. A

two-phase non-overlapping clock generated internally controls the operation of the doubler. During the charge

phase (

transistor switches and is charged to the input voltage. In the pump phase that follows (

φ2), the flying capacitor is

connected between the input and output through similar switches. Stacked atop the input, the charge of the flying

capacitor boosts the output voltage and supplies the load current.

A traditional switched capacitor doubler operating in this manner uses switches with very low on-resistance to

generate an output voltage that is 2× the input voltage. The LM2750 regulates the output voltage by controlling

the resistance of the two input-connected pass-transistor switches in the doubler.

7.2 Functional Block Diagram

7.3 Feature Description

7.3.1 Pre-Regulation

The very low input current ripple of the LM2750, which results from internal pre-regulation, adds very little noise

to the input line. The core of the LM2750 is very similar to that of a basic switched capacitor doubler: it is

composed of four switches and a flying capacitor (external). Regulation is achieved by modulating the on-

resistance of the two switches connected to the input pin (one switch in each phase). The regulation is done

before the voltage doubling, giving rise to the term pre-regulation. It is pre-regulation that eliminates most of the

input current ripple that is a typical and undesirable characteristic of a many switched capacitor converters.