LP2985-N_15 Datasheet, PDF (18/41 Pages) Texas Instruments – LP2985-N Micropower 150-mA Low-Noise Ultra-Low-Dropout Regulator in SOT-23 and DSBGA Packages Designed for Use with Very Low ESR Output Capacitors

LP2985-N
SNVS018X – MARCH 2000 – REVISED MAY 2015
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A better choice for temperature coefficient in ceramic capacitors is X7R, which holds the capacitance within
±15%. Unfortunately, the larger values of capacitance are not offered by all manufacturers in the X7R dielectric.
Tantalum capacitors are less desirable than ceramics for use as output capacitors because they are more
expensive when comparing equivalent capacitance and voltage ratings in the 1 µF to 4.7 µF 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.
9.2.2.3 ON/OFF Input Operation
The LP2985-N is shut off by driving the ON/OFF input low, and turned on by pulling it high. If this feature is not to
be used, the ON/OFF input should be tied to V_IN to keep the regulator output on at all times.
To assure proper operation, the signal source used to drive the ON/OFF input must be able to swing above and
below the specified turn-on/turn-off voltage thresholds listed in the Electrical Characteristics section under
V_ON/OFF. To prevent mis-operation, the turn-on (and turn-off) voltage signals applied to the ON/OFF input must
have a slew rate which is ≥ 40 mV/µs.
CAUTION
The regulator output voltage cannot be ensured if a slow-moving AC (or DC) signal is
applied that is in the range between the specified turn-on and turn-off voltages listed
under the electrical specification V_ON/OFF (see Electrical Characteristics).
9.2.2.4 Reverse Input-Output Voltage
The PNP power transistor used as the pass element in the LP2985-N 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).
V_IN
V_OUT
PNP
GND
Figure 23. Reverse Current Path
SCHOTTKY DIODE
V_IN
V_OUT
PNP
GND
Figure 24. Reverse Current Protection
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