Schottky

LP2981

Copyright © 2016, Texas Instruments Incorporated

9

LP2981-28, LP2981-29, LP2981-30

LP2981-33, LP2981-50, LP2981A-28

LP2981A-29, LP2981A-30, LP2981A-33, LP2981A-50

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SLVS521G – JULY 2004 – REVISED AUGUST 2016

Product Folder Links: LP2981-28 LP2981-29 LP2981-30 LP2981-33 LP2981-50 LP2981A-28 LP2981A-29 LP2981A-

30 LP2981A-33 LP2981A-50

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Copyright © 2004–2016, Texas Instruments Incorporated

7.4 Device Functional Modes

7.4.1 ON/OFF Operation

The LP2981 allows for a shutdown mode through the ON/OFF pin. If the shutdown feature is not used, ON/OFF

must be connected to the input to ensure that the regulator is on at all times. To drive ON/OFF:

•

A LOW (

≤0.3 V) turns the regulator OFF; a HIGH (≥1.6 V) turns it ON.

–

logic supply)

•

The HIGH signal can exceed VIN, but must not exceed the absolute maximum ratings of 20 V for the

ON/OFF pin

•

Apply a signal with a slew rate of

≥40 mV/µs. A slow slew rate can cause the shutdown function to operate

incorrectly

7.4.2 Reverse Input-Output Voltage

An inherent diode is present across the PNP pass element of the LP2981.

Figure 2. Internal PNP Diode Structure

With the anode connected to the output, this diode is reverse-biased during normal operation, because the input

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 approximately 0.3 V,

preventing the regulator's internal diode from forward biasing.

Figure 3. Internal PNP Diode Bypass