Datasheet

LM2767

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SNVS069C –FEBRUARY 2000–REVISED MAY 2013

The selection of capacitors is based on the allowable voltage droop (which equals I

out

), and the desired

output voltage ripple. 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

PARALLELING DEVICES

Any number of LM2767s can be paralleled to reduce the output resistance. Since there is no closed loop

feedback, as found in regulated circuits, stable operation is assured. 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

CASCADING DEVICES

Cascading the LM2767s is an easy way to produce a greater voltage (A two-stage cascade circuit is shown in

Figure 16).

The effective output resistance is equal to the weighted sum of each individual device:

out

= 1.5R

out_1

+ R

out_2

(5)

Note that increasing the number of cascading stages is pracitically limited since it significantly reduces the

efficiency, increases the output resistance and output voltage ripple.

Product Folder Links: LM2767