LP55231 datasheet(12/59 Pages) TI2

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REG

1.5x

1.5 x V

, ROUT

VIN

VOUT

-25

TEMPERATURE °C

100

MAXIMUM

SLOPE VALUE

MINIMUM

SLOPE VALUE

COMP.

LP55231

SNOSCR5D – MARCH 2013 – REVISED DECEMBER 2016

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Feature Description (continued)

Figure 13. Temperature Compensation Principle

7.3.5 Charge Pump Operational Description

7.3.5.1 Overview

The LP55231 includes a pre-regulated switched-capacitor charge pump with a programmable voltage

multiplication of 1 and 1.5×. In 1.5× mode, by combining the principles of a switched-capacitor charge pump and

a linear regulator, a regulated 4.5 V output is generated from the Li-Ion input voltage range. A two-phase non-

overlapping clock generated internally controls the operation of the charge pump. During the charge phase, both

flying capacitors (C1 and C2) are charged from input voltage. In the pump phase that follows, the flying

capacitors are discharged to output. A traditional switched-capacitor charge pump operating in this manner use

switches with very low on-resistance, ideally 0

Ω, to generate an output voltage that is 1.5× the input voltage.

The LP55231 regulates the output voltage by controlling the resistance of the input-connected pass-transistor

switches in the charge pump.

7.3.5.2 Output Resistance

At lower input voltages, the charge pump output voltage may degrade due to effective output resistance (ROUT) of

the charge pump. The expected voltage drop can be calculated by using a simple model for the charge pump

shown in Figure 14.

Figure 14. Charge Pump Output Resistance Model

The model shows a linear pre-regulation block (REG), a voltage multiplier (1.5×), and an output resistance

(ROUT). Output resistance models the output voltage drop that is inherent to switched capacitor converters. The

output resistance is 3.5

Ω (typ.), and it is a function of switching frequency, input voltage, flying capacitors’

capacitance value, internal resistances of the switches and ESR of the flying capacitors. When the output voltage

is in regulation, the regulator in the model controls the voltage V’ to keep the output voltage equal to 4.5 V

(typical).

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