LP2966

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SNVS028E – APRIL 2000 – REVISED APRIL 2013

APPLICATIONS INFORMATION

Input Capacitor Selection

LP2966 requires a minimum input capacitance of 1µF between the input and ground pins to prevent any

impedance interactions with the supply. This capacitor should be located very close to the input pin. This

capacitor can be of any type such as ceramic, tantalum, or aluminium. Any good quality capacitor which has

good tolerance over temperature and frequency is recommended.

Output Capacitor Selection

The LP2966 requires a minimum of 1µF capacitance on each output for proper operation. To insure stability, this

capacitor should maintain its ESR (equivalent series resistance) in the stable region of the ESR curves

(Figure 30 and Figure 31) over the full operating temperature range of the application. The output capacitor

should have a good tolerance over temperature, voltage, and frequency. The output capacitor can be increased

without limit. Larger capacitance provides better stability and noise performance. The output capacitor should be

connected very close to the Vout pin of the IC.

2.2µF

2.2µF

LP2966 works best with Tantalum capacitors. However, the ESR and the capacitance value of these capacitors

vary a lot with temperature, voltage, and frequency. So while using Tantalum capacitors, it should be ensured

that the ESR is within the limits for stability over the full operating temperature range.

For output voltages greater than 2.5V, good quality ceramic capacitors (such as the X7R series from

Taiyoyuden) can also be used with LP2966 in applications not requiring light load operation (< 5mA for the 5V

output option). Once again, it should be ensured that the capacitance value and the ESR are within the limits for

stability over the full operating temperature range.

The ESRD Series Polymer Aluminium Electrolytic capacitors from Cornell Dubilier are very stable over

temperature and frequency. The excellent capacitance and ESR tolerance of these capacitors over voltage,

temperature and frequency make these capacitors very suitable for use with LDO regulators.

Output Noise

Noise is specified in two ways:

Spot Noise or Output Noise Density is the RMS sum of all noise sources, measured at the regulator output, at

a specific frequency (measured with a 1Hz bandwidth). This type of noise is usually plotted on a curve as a

function of frequency.

Total Output Noise or Broad-Band Noise is the RMS sum of spot noise over a specified bandwidth, usually

several decades of frequencies.

Attention should be paid to the units of measurement. Spot noise is measured in units µV/

√Hz or nV/√Hz and

total output noise is measured in µV(rms).

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