LM2767
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SNVS069C –FEBRUARY 2000–REVISED MAY 2013
The selection of capacitors is based on the allowable voltage droop (which equals Iout Rout), 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
Nichicon Corp.
Phone
Website
Capacitor Type
PL & PF series, through-hole aluminum electrolytic
TPS series, surface-mount tantalum
593D, 594D, 595D series, surface-mount tantalum
OS-CON series, through-hole aluminum electrolytic
Ceramic chip capacitors
(847)-843-7500
(843)-448-9411
(207)-324-4140
(619)-661-6835
(800)-831-9172
(800)-348-2496
(408)-432-8020
www.nichicon.com
www.avxcorp.com
www.vishay.com
www.sanyovideo.com
www.murata.com
www.t-yuden.com
www.tokin.com
AVX Corp.
Sprague
Sanyo
Murata
Taiyo Yuden
Tokin
Ceramic chip capacitors
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 C1, while only one output capacitor Cout 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:
Rout = 1.5Rout_1 + Rout_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.
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