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 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.

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

recovery from a fault condition the delay capacitor is used to

10130523

FIGURE 1. Typical Application Circuit

10130524

FIGURE 2. Control Logic Not Used

www.national.com

7