LP5952TL-0.7 NSC [National Semiconductor], LP5952TL-0.7 Datasheet - Page 12

• Manufacturer Part Number: LP5952TL-0.7
• Description: 350mA Dual Rail Linear Regulator
• Manufacturer: NSC [National Semiconductor]

www.national.com
OUTPUT CAPACITOR
The LP5952 is designed specifically to work with very small
ceramic output capacitors. A ceramic capacitor (dielectric
types X7R, Z5U, or Y5V) in the 2.2µF range (up to 10µF) and
with an ESR between 3mΩ to 300mΩ is suitable as C
the LP5952 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 LP5952 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 LP5952.
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. The ex-
ample shows a typical graph comparing different capacitor
case sizes in a Capacitance vs. DC Bias plot. As shown in the
graph, increasing the DC Bias condition can result in the ca-
pacitance value falling below the minimum value given in the
recommended capacitor specifications table (0.47/1.5µF in
this case). Note that the graph shows the capacitance out of
spec for the 0402 case size capacitor at higher bias voltages.
It is therefore recommended that the capacitor manufactur-
ers’ specifications for the nominal value capacitor are con-
sulted for all conditions, as some capacitor sizes (e.g. 0402)
may not be suitable in the actual application.
OUT
OUT
, but these are not as attractive for rea-
pin and returned to a clean analogue
OUT
in
12
The ceramic capacitor’s capacitance can vary with tempera-
ture. The capacitor type X7R, which operates over a temper-
ature range of -55°C to +125°C, will only vary the capacitance
to within ±15%. The capacitor type X5R has a similar toler-
ance over a reduced temperature range of -55°C to +85°C.
Many large value ceramic capacitors, larger than 1µF are
manufactured with Z5U or Y5V temperature characteristics.
Their capacitance can drop by more than 50% as the tem-
perature varies from 25°C to 85°C. Therefore X7R is recom-
mended over Z5U and Y5V in applications where the ambient
temperature will change significantly above or below 25°C.
Tantalum capacitors are less desirable than ceramic for use
as output capacitors because they are more expensive when
comparing equivalent capacitance and voltage ratings in the
1µF to 4.7µF 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 capac-
itor 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.
NO-LOAD STABILITY
The LP5952 will remain stable and in regulation with no ex-
ternal load. This is an important consideration in some cir-
cuits, for example CMOS RAM keep-alive applications.
ENABLE OPERATION
The LP5952 may be switched ON or OFF by a logic input at
the Enable pin, V
on. When the enable pin is low, the regulator output is off and
the device typically consumes 0.1µA.
If the application does not require the Enable switching fea-
ture, the V
output permanently on.
To ensure proper operation, the signal source used to drive
the V
specified turn-on/off voltage thresholds listed in the Electrical
Characteristics section under Enable Control Characteristics,
V
IL
and V
FIGURE 7: Graph Showing A Typical Variation In
EN
input must be able to swing above and below the
IH
EN
.
pin should be tied to V
EN
Capacitance vs DC Bias
. A logic high at this pin will turn the device
BATT
to keep the regulator
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