LP2980-ADJ_15 Datasheet, PDF (9/18 Pages) Texas Instruments – LP2980-ADJ Micropower 50 mA Ultra Low-Dropout Adjustable Voltage Regulator in SOT-23

LP2980-ADJ
www.ti.com
SNVS001E – APRIL 2000 – REVISED APRIL 2013
Be warned that the ESR of a ceramic capacitor is typically low enough to make an LDO oscillate: a 2.2 μF
ceramic demonstrated an ESR of about 15 mΩ when tested. If used as an output capacitor, this will cause
instability (see ESR Curves).
If a ceramic is used on the output of an LDO, a small resistance (about 1Ω) should be placed in series with the
capacitor. If it is used as an input capacitor, no resistor is needed as there is no requirement for ESR on
capacitors used on the input.
EXTERNAL RESISTORS
The output voltage is set using two external resistors (see Basic Application Circuit). It is recommended that the
resistor from the ADJ pin to ground be 51.1 kΩ.
The other resistor (R_ADJ) which connects between V_OUT and the ADJ pin is selected to set V_OUT as given by the
formula:
V_OUT = V_REF + (V_REF x (R_ADJ / 51.1 kΩ))
REVERSE CURRENT PATH
The PNP power transistor used as the pass element in the LP2980-ADJ 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 (See Figure 21).
Figure 21. LP2980–ADJ Reverse Current Path
However, if the input voltage is more than a V_BEbelow the output voltage, this diode will turn ON and current will
flow into the regulator output. In such cases, a parasitic SCR can latch which will allow a high current to flow into
the V_IN pin and out the ground pin, which can damage the part.
The internal diode can also be turned on if the input voltage is abruptly stepped down to a voltage which is a V_BE
below the output voltage.
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. See Figure 22), to limit the reverse voltage across
the LP2980-ADJ to 0.3V (see Absolute Maximum Ratings).
Figure 22. Adding External Schottky Diode Protection
Copyright © 2000–2013, Texas Instruments Incorporated
Product Folder Links: LP2980-ADJ
Submit Documentation Feedback
9