LP2982IM5-2.5/NOPB National Semiconductor, LP2982IM5-2.5/NOPB Datasheet - Page 11

• Manufacturer Part Number: LP2982IM5-2.5/NOPB
• Description: IC REG LDO MICROPOWER SOT23-5
• Manufacturer: National Semiconductor

Specifications of LP2982IM5-2.5/NOPB

• Regulator Topology: Positive Fixed
• Voltage - Output: 2.5V
• Voltage - Input: Up to 16V
• Voltage - Dropout (typical): 0.12V @ 50mA
• Number Of Regulators: 1
• Current - Output: 50mA
• Current - Limit (min): 100mA
• Operating Temperature: -40°C ~ 125°C
• Mounting Type: Surface Mount
• Package / Case: SOT-23-5, SC-74A, SOT-25
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• Other names: LP2982IM5-2.5; LP2982IM5-2.5TR

Application Hints
EXTERNAL CAPACITORS
Like any low-dropout regulator, the external capacitors used
with the LP2982 must be carefully selected to assure regula-
tor loop stability.
Input Capacitor: An input capacitor whose value is
required with the LP2982 (amount of capacitance can be in-
creased without limit).
This capacitor must be located a distance of not more than
0.5 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.
Output Capacitor: The output capacitor must meet both the
requirement for minimum amount of capacitance and E.S.R.
(equivalent series resistance) 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 1, Figure 2).
Important: The output capacitor must maintain its ESR in the
stable region over the full operating temperature to assure
stability. Also, capacitor tolerance and variation with temper-
ature must be considered to assure the minimum amount of
capacitance is provided at all times.
This capacitor should be located not more than 0.5 from the
output pin of the LP2982 and returned to a clean analog
ground.
Low-current Operation: In applications where the load cur-
rent is < 1 mA, special consideration must be given to the
output capacitor.
Circuitry inside the LP2982 is specially designed to reduce
operating (quiescent) current at light loads down to about
65 μA.
The mode of operation which yields this very low quiescent
current also means that the output capacitor ESR is critical.
For optimum stability and minimum output noise, it is recom-
mended that a 10Ω resistor be placed in series with the output
capacitor in any applications where I
CAPACITOR CHARACTERISTICS
Tantalum: Tantalum capacitors are the best choice for use
with the LP2982. Most good quality tantalum can be used with
the LP2982, but check the manufacturer's data sheet to be
sure the ESR is in range.
It is important to remember that ESR increases sharply at
lower temperatures (< 10°C) and a capacitor that is near the
upper limit for stability at room temperature can cause insta-
bility when it gets cold.
In applications which must operate at very low temperatures,
it may be necessary to parallel the output tantalum capacitor
with a ceramic capacitor to prevent the ESR from going up
too high (see next section for important information on ce-
ramic capacitors).
Ceramic: Ceramic capacitors are not recommended for use
at the output of the LP2982. This is because the ESR of a
ceramic can be low enough to go below the minimum stable
value for the LP2982. A good 2.2 μF ceramic was measured
and found to have an ESR of about 15 mΩ, which is low
enough to cause oscillations.
If a ceramic capacitor is used on the output, a 1Ω resistor
should be placed in series with the capacitor.
Aluminum: Because of large physical size, aluminum elec-
trolytic are not typically used with the LP2982. They must
meet the same ESR requirements over the operating tem-
L
< 1 mA.
≥
1 μF is
11
perature range, which is more difficult because of their large
increase in ESR at cold temperature.
An aluminum electrolytic can exhibit an ESR increase of as
much as 50X when going from 20°C to −40°C. Also, some
aluminum electrolytic are not operational below −25°C be-
cause the electrolyte can freeze.
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 val-
ues are −0.015%/nA @ −40°C, −0.021%/nA @ 25°C, and
−0.035%/nA @ +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 will
not have excessive leakage current over the operating tem-
perature range of the application.
A high quality ceramic capacitor which uses either NPO or
COG type dielectric material will typically have very low leak-
age. Small surface mount polypropylene or polycarbonate
film capacitors also have extremely low leakage, but are
slightly larger than ceramics.
FIGURE 1.
FIGURE 2.
5V/2.2 μF ESR Curves
3V/4.7 μF ESR Curves
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1267944
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