LP3992IMF-1.5 National Semiconductor, LP3992IMF-1.5 Datasheet - Page 8

• Manufacturer Part Number: LP3992IMF-1.5
• Description: IC, V REG 30MA, SHUTDOWN, SMD, 3992
• Manufacturer: National Semiconductor

Specifications of LP3992IMF-1.5

• Primary Input Voltage: 2.5V
• Output Voltage: 1.5V
• Dropout Voltage Vdo: 400mV
• No. Of Pins: 5
• Output Current: 30mA
• Voltage Regulator Case Style: SOT-23
• Operating Temperature Range: -40°C To +125°C
• Output Voltage Fixed: 1.5V
• Rohs Compliant: Yes
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

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Application Hints
EXTERNAL CAPACITORS
In common with most regulators, the LP3992 requires exter-
nal capacitors for regulator stability. The LP3992 is specifi-
cally designed for portable applications requiring minimum
board space and smallest 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 LP3992
input pin and ground (this capacitance value may be in-
creased without limit).
This capacitor must be located a distance of not more than
1cm 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 ) 1.0µF over
the entire operating temperature range.
OUTPUT CAPACITOR
The LP3992 is designed specifically to work with very small
ceramic output capacitors. A 1.0µF ceramic capacitor (di-
electric types Z5U, Y5V or X7R) with ESR between 5mΩ to
500mΩ, is suitable in the LP3992 application circuit.
For this device the output capacitor should be connected
between the C
connect the output capacitor directly to the V
case C
It may also be possible to use tantalum or film capacitors at
the device output, C
attractive for reasons of size and cost (see the section
Capacitor Characteristics).
The output capacitor must meet the requirement for the
minimum value of capacitance and also have an ESR value
that is within the range 5mΩ to 500mΩ for stability.
NO-LOAD STABILITY
The LP3992 will remain stable and in regulation with no
external load. This is an important consideration in some
circuits, for example CMOS RAM keep-alive applications.
CAPACITOR CHARACTERISTICS
The LP3992 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
OUT
should be left open-circuit or tied directly to V
OUT
pin and ground. It is also possible to
OUT
(or V
OUT
), but these are not as
OUT
pin. In this
OUT
.
8
capacitors are the smallest, least expensive and have the
lowest ESR values, thus making them best for eliminating
high frequency noise. The ESR of a typical 1µF ceramic
capacitor is in the range of 20mΩ to 40mΩ, which easily
meets the ESR requirement for stability for the LP3992.
The temperature performance of ceramic capacitors varies
by type. Most large value ceramic capacitors ( ≥ 2.2µF) are
manufactured with Z5U or Y5V temperature characteristics,
which results in the capacitance dropping by more than 50%
as the temperature goes from 25˚C to 85˚C.
A better choice for temperature coefficient in a ceramic
capacitor is X7R. This type of capacitor is the most stable
and holds the capacitance within
ture range.
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
capacitor 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.
SHUTDOWN AND ENABLE
The LP3992 features an active low shutdown pin, V
which turns the device off when pulled low. The device
output is enabled when the shutdown pin is pulled high. In
the shutdown mode the regulator output is off and the device
typically consumes 3nA.
If the application does not require the shutdown feature, the
V
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 V
FAST TURN ON AND OFF
The controlled shutdown feature of the device provides a
fast turn off by discharging the output capacitor via an inter-
nal FET device. This discharge is current limited by the
RDS
circuitry within the reference block allowing a very fast ramp
of the output voltage to reach the target voltage.
SD
ON
pin should be tied to V
SD
of this switch. Fast turn-on is guaranteed by control
input must be able to swing above and below the
IN
to keep the regulator output
IL
and V
±
15% over the tempera-
IH
.
SD
,