Datasheet

LM2766

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SNVS071B –MARCH 2000–REVISED MAY 2013

CAPACITOR SELECTION

As discussed in the Positive Voltage Doubler section, 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

(3)

Where I

(V+) is the quiescent power loss of the IC device, and I

out

is the conversion loss associated with the

switch on-resistance, the two external capacitors and their ESRs.

The selection of capacitors is based on the specifications of the dropout voltage (which equals I

out

), the

output voltage ripple, and the converter efficiency. Low ESR capacitors (Table 1) are recommended to maximize

efficiency, reduce the output voltage drop and voltage ripple.

Table 1. Low ESR Capacitor Manufacturers

Manufacturer Phone Website Capacitor Type

Nichicon Corp. (847)-843-7500 www.nichicon.com PL & PF series, through-hole aluminum electrolytic

AVX Corp. (843)-448-9411 www.avxcorp.com TPS series, surface-mount tantalum

Sprague (207)-324-4140 www.vishay.com 593D, 594D, 595D series, surface-mount tantalum

Sanyo (619)-661-6835 www.sanyovideo.com OS-CON series, through-hole aluminum electrolytic

Murata (800)-831-9172 www.murata.com Ceramic chip capacitors

Taiyo Yuden (800)-348-2496 www.t-yuden.com Ceramic chip capacitors

Tokin (408)-432-8020 www.tokin.com Ceramic chip capacitors

Other Applications

PARALLELING DEVICES

Any number of LM2766s can be paralleled to reduce the output resistance. Each device must have its own

pumping capacitor C

, while only one output capacitor C

out

is needed as shown in Figure 15. The composite

output resistance is:

(4)

Figure 15. Lowering Output Resistance by Paralleling Devices

Product Folder Links: LM2766