battery drops to less than 60 µA. With the possibility in many

applications for V

nected in a system through long lengths of wire, the ESD

protection of these pins has been increased to 12 kV with the

addition of small input bypass capacitors.

An output bypass capacitor of at least 0.1µF is required for

stability (47 µF is recommended). An input capacitor of 1 µF

or larger is recommended to improve line transient and noise

performance.

With the Keep-Alive input, a system microprocessor has the

ability to keep the regulator ON (with a logic “0” on

Keep-Alive) after the ON/OFF input has been commanded

OFF. A power-down sequence, when system variables are

typically stored in programmable memory, can be executed

and take as much time as necessary. At the end of the op-

eration the micro then pulls Keep-Alive high and the regula-

tor and system turn OFF and revert to the low quiescent cur-

rent 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.

Conventional load dump protection is built in to withstand up

to +60V and −50V transients. A 1 k

Ω 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 LM9074 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 LM9074.

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 re-

covery 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:

DS101305-23

FIGURE 1. Typical Application Circuit

DS101305-24

FIGURE 2. Control Logic Not Used

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