LM2664

SNVS005E – NOVEMBER 1999 – REVISED DECEMBER 2014

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Figure 15. Combining LM2664 with LP2980 to Make a Negative Adjustable Regulator

9.2.2.5 Output Capacitor Selection

As discussed in Detailed Design Requirements, 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

(11)

Where IQ(V+) is the quiescent power loss of the IC device, and IL

2R

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 Iout ROUT), the

output voltage ripple, and the converter efficiency. Table 1 lists recommendations to maximize efficiency, reduce

the output voltage drop and voltage ripple.

Table 1. Low ESR Capacitor Manufacturers

MANUFACTURER

CAPACITOR TYPE

Nichicon Corp.

PL & PF series, through-hole aluminum electrolytic

AVX Corp.

TPS series, surface-mount tantalum

Sprague

593D, 594D, 595D series, surface-mount tantalum

Sanyo

OS-CON series, through-hole aluminum electrolytic

Murata

Ceramic chip capacitors

Taiyo Yuden

Ceramic chip capacitors

Tokin

Ceramic chip capacitors

9.2.3 Application Curve

Figure 16. Efficiency vs Load Current

12

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