lm9073 National Semiconductor Corporation, lm9073 Datasheet - Page 12

• Manufacturer Part Number: lm9073
• Description: Dual High Current Low-dropout System Regulator
• Manufacturer: National Semiconductor Corporation

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Application Information
various system variables in EPROM for example. With the
controller in command of the Keep-Alive interval these tasks
can take whatever time necessary to complete.
To initiate the Keep-Alive routine before actual power down,
it is important for the system controller to know when the
system has been switched OFF. To eliminate any interface
between the controller and the ON/OFF switch and poten-
tially noisy unregulated input supply, and simple logic
scheme shown in Figure 6 can be used. With this circuitry
the Reset output form the LM9073 provides the ON/OFF
sensing input to the controller.
When switched OFF, the main regulator output will fall out of
regulation and generate a low logic level on the Reset out-
put. This input to the controller provides the switch OFF
indication and initiates the Keep-Alive interval.
(Continued)
FIGURE 5. Basic Keep-Alive Operation
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When completed the controller takes the Keep-Alive input to
a low level and the entire system shuts down. The LM9073
powers down to a low quiescent current mode with less than
100µA drawn from the input supply.
Control of the Keep-Alive duration is set by a logic 1 on the
Keep-Alive output line from the system controller. This high
level prevents the Reset output from resetting the entire
system and also gates the Keep-Alive input signal to the
LM9073. The inverted Reset signal provides a logic 1 to the
Keep-Alive input of the LM9073.
The Main output will only drop out of regulation for a very
short time before the Keep-Alive input turns it back on.
The Reset output remains low for the delay time interval.
When it turns high the Main output switches OFF and back
ON again very quickly. This continues until the system con-
troller takes the Keep-Alive output line to a logic low level.
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