LP2980-N_16 Datasheet, PDF (14/30 Pages) Texas Instruments – Micropower 50-mA Ultra Low-Dropout Regulator in SOT-23 Package

LP2980-N
SNOS733O – APRIL 2000 – REVISED JUNE 2015
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8.2.2 Detailed Design Procedure
At 50-mA loading, the dropout of the LP2980-N has 225-mV maximum dropout over temperature, thus an 1700-
mV headroom is sufficient for operation over both input and output voltage accuracy. The efficiency of the
LP2980-N in this configuration is V_OUT / V_IN = 66.7%. To achieve the smallest form factor, the SOT-23 package is
selected. Input and output capacitors are selected in accordance with the Output Capacitor Recommendation
section. With an efficiency of 66.7% and a 50-mA maximum load, the internal power dissipation is 85 mW, which
corresponds to a 14.9°C junction temperature rise for the SOT-23 package. With an 85°C maximum ambient
temperature, the junction temperature is at 99.9°C.
8.2.2.1 Output Capacitor Recommendation
Like any low-dropout regulator, the LP2980-N requires an output capacitor to maintain regulator loop stability.
This capacitor must be selected to meet the requirements of minimum capacitance and equivalent series
resistance (ESR) range. It is not difficult to find capacitors which meet the criteria of the LP2980-N, as the
acceptable capacitance and ESR ranges are wider than for most other LDOs.
In general, the capacitor value must be at least 1 μF (over the actual ambient operating temperature), and the
ESR must be within the range indicated in Figure 31, Figure 32, and Figure 33. It should be noted that, although
a maximum ESR is shown in these figures, it is very unlikely to find a capacitor with an ESR that high.
8.2.2.1.1 Tantalum Capacitors
Surface-mountable solid tantalum capacitors offer a good combination of small physical size for the capacitance
value, and an ESR in the range needed by the LP2980-N.
The results of testing the LP2980-N stability with surface-mount solid tantalum capacitors show good stability
with values of at least 1 μF. The value can be increased to 2.2 μF (or more) for even better performance,
including transient response and noise.
Small value tantalum capacitors that have been verified as suitable for use with the LP2980-N are shown in
Table 1. Capacitance values can be increased without limit.
8.2.2.1.2 Aluminum Electrolytic Capacitors
Although probably not a good choice for a production design, because of relatively large physical size, an
aluminum electrolytic capacitor can be used in the design prototype for an LP2980-N regulator. A value of at
least 1 μF should be used, and the ESR must meet the conditions of Figure 31, Figure 32, and Figure 33. If the
operating temperature drops below 0°C, the regulator may not remain stable, as the ESR of the aluminum
electrolytic capacitor will increase and may exceed the limits indicated in Figure 31, Figure 32, and Figure 33.
Table 1. Surface-Mount Tantalum Capacitor Selection Guide
1-μF SURFACE-MOUNT TANTALUM CAPACITORS
MANUFACTURER
PART NUMBER
Kemet
T491A105M010AS
NEC
NRU105M10
Siemens
B45196-E3105-K
Nichicon
F931C105MA
Sprague
293D105X0016A2T
2.2-μF SURFACE-MOUNT TANTALUM CAPACITORS
MANUFACTURER
PART NUMBER
Kemet
T491A225M010AS
NEC
NRU225M06
Siemens
B45196/2.2/10/10
Nichicon
F930J225MA
Sprague
293D225X0010A2T
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