LP5951MGX-2.8/NOPB National Semiconductor, LP5951MGX-2.8/NOPB Datasheet - Page 9

• Manufacturer Part Number: LP5951MGX-2.8/NOPB
• Description: IC REG LDO 150MA 2.8V SC70-5
• Manufacturer: National Semiconductor

Specifications of LP5951MGX-2.8/NOPB

• Regulator Topology: Positive Fixed
• Voltage - Output: 2.8V
• Voltage - Input: Up to 5.5V
• Number Of Regulators: 1
• Current - Output: 150mA
• Operating Temperature: -40°C ~ 125°C
• Mounting Type: Surface Mount
• Package / Case: SC-70-5, SC-88A, SOT-323-5, SOT-353, 5-TSSOP
• For Use With: LP5951MF-2.5EV - BOARD EVALUATION LP5951MF-2.5LP5951MF-1.8EV - BOARD EVALUATION LP5951MF-1.8
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• Voltage - Dropout (typical): -
• Current - Limit (min): -
• Other names: LP5951MGX-2.8

Application Hints
POWER DISSIPATION AND DEVICE OPERATION
The permissible power dissipation for any package is a mea-
sure of the capability of the device to pass heat from the power
source, the junctions of the IC, to the ultimate heat sink, the
ambient environment. Thus the power dissipation is depen-
dent on the ambient temperature and the thermal resistance
across the various interfaces between the die and ambient
air.
As stated in
allowable power dissipation for the device in a given package
can be calculated using the equation:
P
With a θ
returns a value of 454 mW with a maximum junction temper-
ature of 125°C at T
The actual power dissipation across the device can be esti-
mated by the following equation:
P
This establishes the relationship between the power dissipa-
tion allowed due to thermal consideration, the voltage drop
across the device, and the continuous current capability of the
device. These two equations should be used to determine the
optimum operating conditions for the device in the application.
EXTERNAL CAPACITORS
As is common with most regulators, the LP5951 requires ex-
ternal capacitors to ensure stable operation. The LP5951 is
specifically designed for portable applications requiring mini-
mum board space and the smallest size components. These
capacitors must be correctly selected for good performance.
INPUT CAPACITOR
An input capacitor is required for stability. It is recommended
that a 1.0µF capacitor be connected between the LP5951 in-
put pin and ground (this capacitance value 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 analogue
ground. Any good quality ceramic, tantalum, or film capacitor
may be used at the input.
Important: Tantalum capacitors can suffer catastrophic fail-
ures due to surge current when connected to a low-
impedance source of power (like a battery or a 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 the ESR (Equivalent Series
Resistance) on the input capacitor, but tolerance and tem-
perature coefficient must be considered when selecting the
capacitor to ensure the capacitance will remain
the entire operating temperature range.
OUTPUT CAPACITOR
The LP5951 is designed specifically to work with very small
ceramic output capacitors. A ceramic capacitor (dielectric
types X7R, Z5U, or Y5V) in the 1.0µF range (up to 47µF) and
D
D
= (T
≈
(V
J(MAX)
IN
JA
- V
= 220°C/W, the device in the SOT23-5 package
(Note
OUT
- T
A
) * I
) / θ
5) in the electrical specification section, the
A
OUT
of 25°C.
JA
≥
0.7µF over
9
with ESR between 3 mΩ to 500 mΩ is suitable in the LP5951
application circuit.
This capacitor must be located a distance of not more than
1cm from the V
ground.
It is also possible to use tantalum or film capacitors at the
device output, V
sons of size and cost (see the section Capacitor Character-
istics).
CAPACITOR CHARACTERISTICS
The LP5951 is designed to work with ceramic capacitors on
the output to take advantage of the benefits they offer. For
capacitance values in the range of 1µF to 4.7µF, ceramic ca-
pacitors are the smallest, least expensive and have the lowest
ESR values, thus making them best for eliminating high fre-
quency noise. The ESR of a typical 1µF ceramic capacitor is
in the range of 3mΩ to 40mΩ, which easily meets the ESR
requirement for stability for the LP5951.
For both input and output capacitors, careful interpretation of
the capacitor specification is required to ensure correct device
operation. The capacitor value can change greatly, depend-
ing on the operating conditions and capacitor type.
In particular, the output capacitor selection should take ac-
count of all the capacitor parameters, to ensure that the
specification is met within the application. The capacitance
can vary with DC bias conditions as well as temperature and
frequency of operation. Capacitor values will also show some
decrease over time due to aging. The capacitor parameters
are also dependant on the particular case size, with smaller
sizes giving poorer performance figures in general. As an ex-
ample,
capacitor case sizes in a Capacitance vs. DC Bias plot. As
shown in the graph, increasing the DC Bias condition can re-
sult in the capacitance value falling below the minimum value
given in the recommended capacitor specifications table
(0.7µF in this case). Note that the graph shows the capaci-
tance out of spec for the 0402 case size capacitor at higher
bias voltages. It is therefore recommended that the capacitor
manufacturers’ specifications for the nominal value capacitor
are consulted for all conditions, as some capacitor sizes (e.g.
0402) may not be suitable in the actual application.
FIGURE 1. Graph Showing A Typical Variation In
Figure 1
OUT
OUT
shows a typical graph comparing different
Capacitance vs DC Bias
, but these are not as attractive for rea-
pin and returned to a clean analogue
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