LP2982 Datasheet, PDF (18/28 Pages) National Semiconductor (TI) – Micropower 50 mA Ultra Low-Dropout Regulator

LP2982
SNVS128K – MARCH 2000 – REVISED JUNE 2016
www.ti.com
In any application where the output voltage may be higher than the input voltage, an external Schottky diode
must be connected from V_IN to V_OUT (cathode on V_IN, anode on V_OUT; see Figure 39), to limit the reverse voltage
across the LP2982 to 0.3 V (see Absolute Maximum Ratings).
SCHOTTKY DIODE
V_IN
V_OUT
PNP
GND
Figure 39. Adding External Schottky Diode Protection
8.2.2.4 ON/OFF Input Operation
The LP2982 is shut off by pulling the ON/OFF input low, and turned on by driving the input high. If this feature is
not to be used, the ON/OFF input should be tied to V_IN to keep the regulator on at all times (the ON/OFF input
must not be left floating).
To ensure proper operation, the signal source used to drive the ON/OFF input must be able to swing above and
below the specified turnon/turnoff voltage thresholds which specify an ON or OFF state (see Electrical
Characteristics).
The ON/OFF signal may come from either a totem-pole output, or an open-collector output with pullup resistor to
the LP2982 input voltage or another logic supply. The high-level voltage may exceed the LP2982 input voltage,
but must remain within the Absolute Maximum Ratings for the ON/OFF pin.
It is also important that the turnon/turnoff voltage signals applied to the ON/OFF input have a slew rate which is
greater than 40 mV/μs.
NOTE
IMPORTANT: The regulator shutdown function does not operate correctly if a slow-moving
signal is applied to the ON/OFF input.
8.2.2.5 Power Dissipation
Knowing the device power dissipation and proper sizing of the thermal plane connected to the tab or pad is
critical to ensuring reliable operation. Device power dissipation depends on input voltage, output voltage, and
load conditions and can be calculated with Equation 1.
P_D(MAX) = (V_IN(MAX) – V_OUT) × I_OUT
(1)
Power dissipation can be minimized, and greater efficiency can be achieved, by using the lowest available
voltage drop option that is greater than the dropout voltage (V_DO). However, keep in mind that higher voltage
drops result in better dynamic (that is, PSRR and transient) performance.
On the LP2982 SOT-23 (DBV) package, the primary conduction path for heat is through the five leads to the
PCB. The ground pin (pin 2) is attached directly to the back side of the die and should be accorded extra copper
area on the PCB. The maximum allowable junction temperature (T_J(MAX)) determines maximum power dissipation
allowed (P_D(MAX)) for the device package. Power dissipation and junction temperature are most often related by
the junction-to-ambient thermal resistance (R_θJA) of the combined PCB and device package and the temperature
of the ambient air (T_A), according to Equation 2 or Equation 3:
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