LP2966IMMX-3325 Datasheet, PDF (11/21 Pages) Texas Instruments – Dual 150mA Ultra Low-Dropout Regulator

LP2966
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APPLICATIONS INFORMATION
SNVS028E – APRIL 2000 – REVISED APRIL 2013
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.
Figure 30. ESR Curve for V_OUT = 5V and C_OUT =
2.2µF
Figure 31. ESR Curve for V_OUT = 3.3V and C_OUT =
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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