lm9070t National Semiconductor Corporation, lm9070t Datasheet - Page 10

• Manufacturer Part Number: lm9070t
• Description: Low-dropout System Voltage Regulator With Keep-alive On/off Control
• Manufacturer: National Semiconductor Corporation

www.national.com
Application Information
series with the input. The drop in input current may create a
positive input voltage transient which may take the PNP out
of saturation. If the input voltage is held constant at the
threshold where the PNP is going in and out of saturation, an
oscillation may be created.
This is only observed where significant series inductance is
present in the input supply line and when the rise and fall
time of the input supply is very slow. If the application and
removal of the input voltage changes at a rate greater than
500 mV/µs, the input voltage moves through the dropout
region of operation (V
oscillation to be established.
IN
of 3V to 5.5V) too quickly for an
(Continued)
10
MICROPROCESSOR SYSTEM REGULATOR WITH
KEEP-ALIVE INTERVAL AT TURN-OFF
The following circuit illustrates a system application utilizing
both of the logic control inputs of the LM9070. Closing the
ON/OFF switch powers ON the system. Once powered, the
system controller sets the Keep-Alive line low. The NPN
transistor is used only to signal the controller that the ON/
OFF switch has been opened and the system is to be turned
OFF. Upon detecting this high level at the ON/OFF Sense
input line, the controller can then perform a power down
routine. The system will remain fully powered until the con-
troller commands total shut down by taking the Keep-Alive
line high. The system then shuts OFF and reverts to a very
low current drain standby condition until switched back on.