LP2954 Datasheet, PDF (13/28 Pages) National Semiconductor (TI) – 5V and Adjustable Micropower Low-Dropout Voltage Regulators

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8 Application and Implementation
LP2954, LP2954A
SNVS096E – JUNE 1999 – REVISED JULY 2016
NOTE
Information in the following applications sections is not part of the TI component
specification, and TI does not warrant its accuracy or completeness. TI’s customers are
responsible for determining suitability of components for their purposes. Customers should
validate and test their design implementation to confirm system functionality.
8.1 Application Information
The LP2954-N is a linear voltage regulator operating from 2.3 V to 30 V on the input and regulated output
voltage of 5 V with typical 0.5% accuracy (LP2954AI) and 250 mA maximum output current. For linear voltage
regulator the efficiency is defined by the ratio of output voltage to input voltage (efficiency = V_OUT/V_IN). To
achieve high efficiency, the dropout voltage (V_IN – V_OUT) must be as small as possible, thus requiring a very low
dropout LDO. Successfully implementing an LDO in an application depends on the application requirements. If
the requirements are simply input voltage and output voltage, compliance specifications (such as internal power
dissipation or stability) must be verified to ensure a solid design. If timing, start-up, noise, PSRR, or any other
transient specification is required, the design becomes more challenging.
8.2 Typical Application
V_IN
1 µF
IN
OUT
GND
5 V OUT
2.2 µF ^LOAD
Figure 18. LP2954 Typical Application
8.2.1 Design Requirements
For typical LDO applications, use the parameters listed in Table 1.
DESIGN PARAMETER
Input voltage
Output voltage
Output current
RMS noise, 10 Hz to100 kHz
Table 1. Design Parameters
EXAMPLE VALUE
2.5 V to 30 V
1.23 V to 29 V
250 mA (maximum)
260 μV_RMS
8.2.2 Detailed Design Procedure
8.2.2.1 External Capacitors
A 2.2 μF (or greater) capacitor is required between the OUT pin and GND to assure stability (refer to Figure 20).
Without this capacitor, the device may oscillate. Most types of tantalum or aluminum electrolytic capacitors work
here. Film-type capacitors work, but are more expensive. Many aluminum electrolytics contain electrolytes which
freeze at −30°C, which requires the use of solid tantalums below −25°C. The important parameters of the
capacitor are an equivalent series resistance (ESR) of about 5 Ω or less and a resonant frequency above 500
kHz (the ESR may increase by a factor of 20 or 30 as the temperature is reduced from 25°C to −30°C). The
value of this capacitor may be increased without limit. At lower values of output current, less output capacitance
is required for stability. The capacitor can be reduced to 0.68 μF for currents below 10 mA or 0.22 μF for currents
below 1 mA.
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Product Folder Links: LP2954 LP2954A
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