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LM2665

SNVS009H – NOVEMBER 1999 – REVISED MARCH 2016

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Copyright © 1999–2016, Texas Instruments Incorporated

9.2.1.2 Detailed Design Requirements

9.2.1.2.1

Positive Voltage Doubler

The output characteristics of this circuit can be approximated by an ideal voltage source in series with a

internal MOSFET switches, the oscillator frequency, the capacitance and equivalent series resistance (ESR) of

where

•

(1)

The peak-to-peak output voltage ripple is determined by the oscillator frequency, the capacitance and ESR of the

(2)

High capacitance, low-ESR capacitors can reduce both the output resistance and the voltage ripple.

pin. Voltage across OUT and GND must be larger than 1.8 V to insure the operation of the oscillator. During

enough current carrying capability to charge the output capacitor at start-up, as well as a low forward voltage to

prevent the internal parasitic diode from turning-on. A Schottky diode like 1N5817 can be used for most

applications. If the input voltage ramp is less than 10 V/ms, a smaller Schottky diode like MBR0520LT1 can be

used to reduce the circuit size.

9.2.1.2.2

Capacitor Selection

As discussed in Positive Voltage Doubler, the output resistance and ripple voltage are dependent on the

capacitance and ESR values of the external capacitors. The output voltage drop is the load current times the

output resistance, and the power efficiency is:

where

•

•

ESRs.

(3)

output voltage ripple, and the converter efficiency. Low ESR capacitors are recommended to maximize efficiency,

reduce the output voltage drop and voltage ripple.

9.2.1.2.3

Paralleling Devices

Any number of LM2665 devices can be paralleled to reduce the output resistance. Each device must have its

composite output resistance is:

(4)