Datasheet

LP2980-ADJ

SNVS001E –APRIL 2000–REVISED APRIL 2013

www.ti.com

APPLICATION HINTS

EXTERNAL CAPACITORS

Like any low-dropout regulator, the external capacitors must be selected carefully to assure regulator loop

stability.

INPUT CAPACITOR: An input capacitor whose value is ≥1 μF is required (the amount of capacitance may be

increased without limit).

Any good quality Tantalum or Ceramic capacitor may be used here. The capacitor must be located not more

than 0.5″ from the input pin and returned to a clean analog ground.

OUTPUT CAPACITOR: The output capacitor must meet both the requirement for minimum amount of

capacitance and E.S.R. (Equivalent Series Resistance) for stable operation.

Curves are provided below which show the allowable ESR of the output capacitor as a function of load current

for both 2.2 μF and 4.7 μF. A solid Tantalum capacitor is the best choice for the output.

Figure 19. 2.2 μF ESR Curves Figure 20. 4.7 μF ESR Curves

IMPORTANT: The output capacitor must maintain its ESR in the stable region over the full operating

temperature range to assure stability. Also, capacitor tolerance and variation with temperature must be

considered to assure the minimum amount of capacitance is provided at all times.

Note that this capacitor must be located not more than 0.5” from the output pin and returned to a clean analog

ground.

FEED-FORWARD CAPACITOR: A 7 pF feed-forward capacitor is required (see Basic Application Circuit). The

function of this capacitor is to provide the lead compensation necessary for loop stability.

A temperature-stable ceramic capacitor (type NPO or COG) should be used here.

CAPACITOR CHARACTERISTICS

TANTALUM: The best capacitor choice for the LP2980-ADJ output is solid Tantalum. The ESR of a good quality

Tantalum is almost perfectly centered in the middle of the “stable” range of the ESR curve (about 0.5Ω–1Ω).

The temperature stability of Tantalums is typically very good, with a total variation of only about 2:1 over the

temperature range of −40°C to +125°C (ESR increases at colder temperatures).

Off-brand capacitors should be avoided, as some poor quality Tantalums are seen with ESR's > 10Ω, and this

usually causes oscillation problems.

One caution about Tantalums if they are used on the input: the ESR of a Tantalum is low enough that it can be

destroyed by surge current if powered up from a low impedance source (like a battery) that has no limit on inrush

current. In these cases, use a ceramic input capacitor which does not have this problem.

CERAMIC: Ceramics are generally larger and more costly than Tantalums for a given amount of capacitance.

Also, they have a very low ESR which is quite stable with temperature.

Product Folder Links: LP2980-ADJ