LP2989LV_15 Datasheet, PDF (14/26 Pages) Texas Instruments – Micropower and Low-Noise, 500-mA Ultra Low-Dropout Regulator for Use With Ceramic Output Capacitors

LP2989LV
SNVS086K – MAY 2000 – REVISED JULY 2015
www.ti.com
8.2.2.3.2 Tantalum
Tantalum output capacitors are not recommended for use with the LP2989LV; they are less desirable than
ceramics for use as output capacitors because they are typically more expensive when comparing equivalent
capacitance and voltage ratings in the 1 µF to 10 µF range
Another important consideration is that tantalum capacitors have higher ESR values than equivalent size
ceramics; 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.
Most 10-µF tantalum capacitors have ESR values higher than 0.5 Ω maximum limit required to make the
LP2989LV stable. Also note that the ESR of a typical tantalum increases about 2:1 as the temperature goes from
25°C down to −40°C, so some guard band must be allowed.
8.2.2.3.3 Film
Polycarbonate and polypropelene film capacitors have excellent electrical performance: their ESR is the lowest of
the three types listed, their capacitance is very stable with temperature, and DC leakage current is extremely low.
One disadvantage is that film capacitors are larger in physical size than ceramic or tantalum which makes film a
poor choice for either input or output capacitors.
However, their low leakage makes them a good choice for the noise bypass capacitor. Because the required
amount of capacitance is only 0.01 µF, small surface-mount film capacitors are available in this size.
8.2.2.4 Reverse Input-Output Voltage
The PNP power transistor used as the pass element in the LP2989LV has an inherent diode connected between
the regulator output and input.
During normal operation (where the input voltage is higher than the output) this diode is reverse-biased.
However, if the output is pulled above the input, this diode turns on, and current flows into the regulator output.
In such cases, a parasitic SCR can latch which allows high current to flow into V_IN can damage the part.
In any application where the output may be pulled above the input, an external Schottky diode must be
connected from V_IN to V_OUT (cathode on V_IN, anode on V_OUT), to limit the reverse voltage across the LP2989LV to
0.3 V (see Absolute Maximum Ratings).
8.2.3 Application Curves
Figure 14. Line Transient Response
Figure 15. Load Transient Response
14
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