SLVS521B JULY 2004 REVISED OCTOBER 2004
14
POST OFFICE BOX 655303
DALLAS, TEXAS 75265
APPLICATION INFORMATION
reverse input-output voltage
An inherent diode is present across the PNP pass element of the LP2981.
VOUT
VIN
With the anode connected to the output, this diode is reverse biased during normal operation, since the input
voltage is higher than the output. However, if the output is pulled one V
BE
higher than the input, or if the input
is abruptly stepped below the output, this diode is forward biased and can cause a parasitic silicon-controlled
rectifier (SCR) to latch, resulting in current flowing from the output to the input (values in excess of 100 mA can
cause damage). Thus, to prevent possible damage to the regulator in any application where the output may be
pulled above the input, an external Schottky diode must be connected between the output and input. With the
anode on output, this Schottky limits the reverse voltage across the output and input pins to 0.3 V, preventing
the regulator’s internal diode from forward biasing.
VOUT
VIN
Schottky
LP2981
pin 4: NC
Pin 4 must be left OPEN. Do not connect anything to this pin, as it is used for post package trim.