LP2992AIM5-3.3 National Semiconductor, LP2992AIM5-3.3 Datasheet - Page 12

• Manufacturer Part Number: LP2992AIM5-3.3
• Description: IC, LDO VOLT REG, 3.3V, 250mA, 5-SOT-23
• Manufacturer: National Semiconductor

Specifications of LP2992AIM5-3.3

• Primary Input Voltage: 16V
• Output Voltage Fixed: 3.3V
• Dropout Voltage Vdo: 450mV
• No. Of Pins: 5
• Output Current: 250mA
• Operating Temperature Range: -40°C To +125°C
• Termination Type: SMD
• Lead Free Status / RoHS Status: Contains lead / RoHS non-compliant

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Application Hints
EXTERNAL CAPACITORS
Like any low-dropout regulator, the LP2992 requires external
capacitors for regulator stability. These capacitors must be
correctly selected for good performance.
Input Capacitor
An input capacitor whose capacitance is
between the LP2992 input and ground (the amount of capac-
itance may be increased without limit).
This capacitor must be located a distance of not more than 1
cm from the input pin and returned to a clean analog ground.
Any good quality ceramic, tantalum, or film capacitor may be
used at the input.
Important: Tantalum capacitors can suffer catastrophic fail-
ure due to surge current when connected to a low-impedance
source of power (like a battery or very large capacitor). If a
Tantalum capacitor is used at the input, it must be guaranteed
by the manufacturer to have a surge current rating sufficient
for the application.
There are no requirements for ESR on the input capacitor, but
tolerance and temperature coefficient must be considered
when selecting the capacitor to ensure the capacitance will
be
Output Capacitor:
The LP2992 is designed specifically to work with ceramic out-
put capacitors, utilizing circuitry which allows the regulator to
be stable across the entire range of output current with an
output capacitor whose ESR is as low as 5 mΩ. It may also
be possible to use Tantalum or film capacitors at the output,
but these are not as attractive for reasons of size and cost
(see next section Capacitor Characteristics).
The output capacitor must meet the requirement for minimum
amount of capacitance and also have an ESR (equivalent se-
ries resistance) value which is within the stable range. Curves
are provided which show the stable ESR range as a function
of load current (see ESR graph below).
Important: The output capacitor must maintain its ESR within
the stable region over the full operating temperature range of
the application to assure stability.
The LP2992 requires a minimum of 4.7 µF on the output (out-
put capacitor size can be increased without limit).
It is important to remember that capacitor tolerance and vari-
ation with temperature must be taken into consideration when
selecting an output capacitor so that the minimum required
≥
1 µF over the entire operating temperature range.
≥
1 µF is required
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amount of output capacitance is provided over the full oper-
ating temperature range. It should be noted that ceramic
capacitors can exhibit large changes in capacitance with tem-
perature (see next section, Capacitor Characteristics).
The output capacitor must be located not more than 1 cm from
the output pin and returned to a clean analog ground.
Noise Bypass Capacitor:
Connecting a 10 nF capacitor to the Bypass pin significantly
reduces noise on the regulator output. It should be noted that
the capacitor is connected directly to a high-impedance circuit
in the bandgap reference.
Because this circuit has only a few microamperes flowing in
it, any significant loading on this node will cause a change in
the regulated output voltage. For this reason, DC leakage
current through the noise bypass capacitor must never ex-
ceed 100 nA, and should be kept as low as possible for best
output voltage accuracy.
The types of capacitors best suited for the noise bypass ca-
pacitor are ceramic and film. High-quality ceramic capacitors
with either NPO or COG dielectric typically have very low
leakage. 10 nF polypropolene and polycarbonate film capac-
itors are available in small surface-mount packages and typ-
ically have extremely low leakage current.
CAPACITOR CHARACTERISTICS
The LP2992 was designed to work with ceramic capacitors
on the output to take advantage of the benefits they offer: for
capacitance values in the 2.2 µF to 10 µF range, ceramics are
the least expensive and also have the lowest ESR values
(which makes them best for eliminating high-frequency
noise). The ESR of a typical 4.7 µF ceramic capacitor is in the
range of 5 mΩ to 10 mΩ, which easily meets the ESR limits
required for stability by the LP2992.
One disadvantage of ceramic capacitors is that their capaci-
tance can vary with temperature. Most large value ceramic
capacitors (
temperature characteristic, which results in the capacitance
dropping by more than 50% as the temperature goes from 25°
C to 85°C.
This could cause problems if a 4.7 µF capacitor were used on
the output since it will drop down to approximately 2.3 µF at
high ambient temperatures (which could cause the LP2992 to
oscillate). If Z5U or Y5V capacitors are used on the output, a
minimum capacitance value of 10 µF must be observed.
A better choice for temperature coefficient in ceramic capac-
itors is X7R, which holds the capacitance within ±15%. Un-
fortunately, the larger values of capacitance are not offered
by all manufacturers in the X7R dielectric.
Tantalum:
Tantalum capacitors are less desirable than ceramics for use
as output capacitors because they are more expensive when
comparing equivalent capacitance and voltage ratings in the
1 µF to 4.7 µF range.
Another important consideration is that Tantalum capacitors
have higher ESR values than equivalent size ceramics. This
means that while it may be possible to find a Tantalum ca-
pacitor with an ESR value within the stable range, it would
have to be larger in capacitance (which means bigger and
more costly) than a ceramic capacitor with the same ESR
value.
It should also be noted that the ESR of a typical Tantalum will
increase about 2:1 as the temperature goes from 25°C down
to −40°C, so some guard band must be allowed.
≥
2.2 µF) are manufactured with the Z5U or Y5V