LP2981 Datasheet, PDF (6/17 Pages) National Semiconductor (TI) – Micropower 100 mA Ultra Low-Dropout Regulator

LP2981
SLVS521F – JULY 2004 – REVISED AUGUST 2008 ......................................................................................................................................................... www.ti.com
APPLICATION INFORMATION
Capacitors
Input Capacitor (C_in)
A minimum value of 1 µF (over the entire operating temperature range) is required at the input of the LP2981. In
addition, this input capacitor should be located within 1 cm of the input pin and connected to a clean analog
ground. There is no Equivalent Series Resistance (ESR) requirement for this capacitor, and the capacitance can
be increased without limit. A good quality ceramic or tantalum capacitor can be used.
Output Capacitor (C_out)
As a PNP regulator, the LP2981 requires the output capacitor to meet both a minimum capacitance and ESR
value. Required ESR values as a function of load current are provided for various output voltages, load currents,
and capacitances (see Figure 2 through Figure 5).
• Minimum C_out: 3.3 µF (can be increased without limit to improve transient response stability margin)
• ESR range: see Figure 2 through Figure 5
It is critical that both the minimum capacitance and ESR requirement be met over the entire operating
temperature range. Depending on the type of capacitor used, both of these parameters can vary significantly with
temperature (see capacitor characteristics section).
Load Current − mA
Figure 2. 5-V/3.3-µF ESR Curves
Load Current − mA
Figure 3. 5-V/10-µF ESR Curves
Load Current − mA
Figure 4. 3-V/3.3-µF ESR Curves
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Load Current − mA
Figure 5. 3-V/10-µF ESR Curves
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