lm9074ep National Semiconductor Corporation, lm9074ep Datasheet - Page 8

• Manufacturer Part Number: lm9074ep
• Description: Enhanced Plastic System Voltage Regulator With Keep-alive On/off Control
• Manufacturer: National Semiconductor Corporation

www.national.com
Application Information
as much time as necessary. At the end of the operation the
micro then pulls Keep-Alive high and the regulator and sys-
tem turn OFF and revert to the low quiescent current standby
mode.
For additional system reliability, consideration has been
made for the possibility of a short circuited load at the output
of the regulator. When the regulator is switched ON, conven-
tional current limiting and thermal shutdown protect the regu-
lator. When the regulator is switched OFF however, a
grounded V
lator output) will force the Keep-Alive input to be low and
thus try to maintain the Keep-Alive mode of operation. With
a shorted load, the drain on the battery could be as high as
1.5A. A separate internal circuit monitors the output voltage
of the regulator. If V
with a shorted load, the Keep-Alive function is logically dis-
abled to ensure that the regulator turns OFF and reverts to
less than a 60 µA load on the battery.
FIGURE 2. Control Logic Not Used
CC
supply to the micro (due to the shorted regu-
OUT
is less than 4V, as would be the case
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Conventional load dump protection is built in to withstand up
to +60V and −50V transients. A 1 kΩ resistor in series with
the ON/OFF and Keep-Alive inputs are recommended to
provide the same level of transient protection for these pins
if required. Protection against reverse polarity battery con-
nections is also built in. With a reversed battery the output of
the LM9074EP will not go more negative than one diode
drop below ground. This will prevent damage to any of the
5V load circuits.
For applications where the control logic is not required the
logic pins should be configured as shown in Figure 2. A
separate device, called the LM9071, can be used. The
LM9071 is available in a 5-lead TO-220 package and does
not provide control logic functions, but still retains all of the
protection features of the LM9074EP.
RESET FLAG
Excessive loading of the output to the point where the output
voltage drops by 300 mV to 500 mV will signal a reset flag to
the micro. This will warn of a V
unpredictable operation of the system. On power-up and
recovery from a fault condition the delay capacitor is used to
hold the micro in a reset condition for a programmable time
interval to allow the system operating voltages and
clock to stabilize before executing code. The typical delay
time interval can be estimated using the following equation:
CC
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supply that may produce