LP2982 Datasheet, PDF (16/28 Pages) National Semiconductor (TI) – Micropower 50 mA Ultra Low-Dropout Regulator

LP2982
SNVS128K – MARCH 2000 – REVISED JUNE 2016
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8.2.2.1.1 Input Capacitor
An input capacitor with a value ≥ 1 μF is required with the LP2982 (amount of capacitance can be increased
without limit).
This capacitor must be located a distance of not more than 0.5 inches from the input pin of the LP2982 and
returned to a clean analog ground. Any good quality ceramic or tantalum can be used for this capacitor.
8.2.2.1.2 Output Capacitor
The output capacitor must meet both the requirement for minimum amount of capacitance and equivalent series
resistance (ESR) value. Curves are provided which show the allowable ESR range as a function of load current
for various output voltages and capacitor values (refer to Figure 40 and Figure 41).
NOTE
Important: The output capacitor must maintain its ESR in the stable region over the full
operating temperature range to ensure stability. Also, capacitor tolerance and variation
with temperature must be considered to ensure the minimum amount of capacitance is
provided at all times.
This capacitor must be located not more than 0.5 inches from the OUT pin of the LP2982 and returned to a clean
analog ground.
V_IN
C_IN
1 µF
ON/OFF
ON
OFF
IN
OUT
ON/OFF BYPASS
GND
V_OUT
C_OUT (MLCC)
2.2 µF (5-V device)
4.7 µF (3-V and 3.3-V devices)
C_BYPASS
0.01 µF
R_ESR
1Ÿ
Figure 37. Typical Application With Ceramic C_OUT Series R
8.2.2.1.3 Bypass Capacitor
The 0.01-μF capacitor connected to the bypass pin to reduce noise must have very low leakage.
The current flowing out of the bypass pin comes from the bandgap reference, which is used to set the output
voltage.
This capacitor leakage current causes the output voltage to decline by an amount proportional to the current.
Typical values are −0.015%/nA at −40°C, −0.021%/nA at 25°C, and −0.035%/nA at 125°C.
This data is valid up to a maximum leakage current of about 500 nA, beyond which the bandgap is so severely
loaded that it can not function.
Care must be taken to ensure that the capacitor selected does not have excessive leakage current over the
operating temperature range of the application.
A high-quality ceramic capacitor which uses either NPO or COG type dielectric material typically has very low
leakage. Small surface mount polypropylene or polycarbonate film capacitors also have extremely low leakage,
but are slightly larger than ceramics.
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